| RECENT PUBLICATIONS |
Table of contents:
| RECENT PUBLICATIONS |
Assessment of turbulence modelling for CFD simulations into hydroturbines: spiral casings
Luis C. Eduardo Oliveira de Souza, Marcelo Dias de Moura, Antonio C.P. Brasil Junior and Håkan Nilsson
17th International Mechanical Engineering Congress (COBEM 2003) at São Paulo (Brazil)
Abstract
Spiral casings are applied to distribute the water, as evenly as possible, to the stay vanes and wicket gates and then to the turbine runner. In a well-designed spiral casing, the pressure head of the fluid should be made available to the runner with minimum loss, hence the analysis of the flow through a spiral casing is important for the design of efficient hydraulic turbines. The goal of this work is based on turbo machines spiral casings three-dimensional flow modeling, simulation and characterization. Governing equations related to their study are used in the mathematical modeling part. Therefore, several turbulence models available will be tested with a finite volume method based commercial software CFX 5.5.1 which generates default tetrahedral meshing. Qualitative and quantitative results validation are proved by workshop benchmark experiments already done, in order these results can obtain a turbulence model that represents better the flow complexity inside spiral casings.
Keywords: Numerical simulation, spiral casings, CFD, Turbulence Models.
Luis C. Eduardo Oliveira de Souza, Marcelo Dias de Moura and Antonio C.P. Brasil Junior, Universidade de Brasília - Departamento de Engenharia Mecânica - Pós-Graduação Laboratório de Energia e Ambiente - LEA CEP 70.910-900 - Brasília - DF - Brasil +55 (61) 307-2314 R236/238 duducastro@yahoo.com. Håkan Nilsson, Department of Thermo and Fluid Dynamics, Chalmers University of Technology, Göteborg, Sweden, hani@chalmers.se
IAHR 2004, Stockholm, 2004
Abstract
When a hydraulic power plant is operating at off-design, a swirling flow exits the runner and is convected through the draft tube. The swirling flow gives rise to several features that decrease the efficiency and/or may damage the construction. As a step towards making reliable numerical predictions of the swirling flow in draft tubes, steady computations in an idealised model have been carried out. The model geometry is a straight conical diffuser and O. G. Dahlhaug of NTNU, Trondheim, Norway, has provided experimental data. In this paper, numerical 3D RANS investigations are quantitatively compared to the available experimental data. Good agreement with experimental data was obtained. The discrepancies are partly reminiscent of the nature of the k- turbulence model that was used in this work.
Given symmetric geometry and boundary conditions, a fluid flow is most often thought to behave in an equally symmetric manner. If the flow is swirling, this is not generally true. Due to the unstable properties of the symmetric solutions for the averaged Navier-Stokes equations, the flow will collapse into an asymmetric mode. In the first computational cases of this paper, the disturbance that triggers the instability is shown to be imperfections in the CAD-geometry.
Also included is a discussion concerning the development of counter-rotating vortices in the boundary layer of swirling flow in a circular pipe.
Keywords: Draft tube, diffuser, swirl, turbulence.
Turbine-99 III workshop, 8-9 December 2005, Porjus, Sweden
Abstract
This paper presents OpenFOAM computational results of the flow in the Hölleforsen hydraulic turbine draft tube model. It is a contribution to the third Turbine-99 workshop on draft tube flow (www.turbine-99.org). The boundary conditions and the wall-function grid of 'Case 1: Steady calculation' is used. Turbulence is modelled using the standard k-epsilon model with wall functions. The results are analysed at sections where detailed measurements are available. Detailed comparisons between the results presented in this paper, computational contributions from other participants, and measurements are available in the workshop proceedings (see www.turbine-99.org).
* Institute of Fluid Mechanics and Hydraulic Machinery, University of Stuttgart, Germany
** Div. of Fluid Dynamics, Dept. of Applied Mech., Chalmers University, Göteborg, Sweden
Conference on Turbulence and Interactions TI2006, May 29 - June 2, 2006, Porquerolles, France
Abstract
Swirling flows are very dominant in applied technical problems, especially hydraulic machinery, and their prediction requires rather sophisticated modelling. At present an applicative method for simulation is Very Large Eddy Simulation (VLES). In VLES large turbulence structures are resolved by an unsteady simulation and the minor structures are modelled with an adequate turbulence model. Therefore turbulence model must distinguish between resolved and unresolved scales. The VLES method also introduces a filtering technique which helps the turbulence model to adapt in accordance with the scales to be modelled. As a basis the modified k-epsilon model of Chen and Kim used with additional streamline curvature correction of Reif. The model is implemented in both FENFLOSS and CALC-PMB CFD codes which are used for simulation of swirling pipe flow and swirling flow through a straight conical diffuser, respectively.
Proceedings of PARA'06, Umeå, 2006
Book: Applied Parallel Computing. State of the Art in Scientific Computing
Book Series: Lecture Notes in Computer Science
Publisher: Springer Berlin / Heidelberg
ISSN 0302-9743 (Print) 1611-3349 (Online)
ISBN 978-3-540-75754-2
Volume Volume 4699/2007
Pages 168-176
Abstract
50% of the electric power in Sweden is generated by water power. Many of the power plants in Sweden are getting old and some major refurbishments are coming up. Due to the development of numerical methods and computer power the last decades Computational Fluid Dynamics (CFD) is to a large extent used as a design tool for this purpose. The general features of the flow in water turbines can be resolved with todays methods and computational power, but in order to study the flow in detail enormous HPC facilities and new methods are required. The present work presents the water turbine field with its HPC requirements, shows some state-of-the-art results from OpenFOAM CFD analysis, and presents a parallel performance analysis on a Linux cluster using an ordinary gigabit interconnect v.s. an Infiniband interconnect.
IAHR 2006, Yokohama, 2006
Abstract
The purpose of this study is to evaluate the newly distributed OpenFOAM (www.openfoam.org) OpenSource CFD tool for turbulent flow in water turbines. The aim is to validate the OpenFOAM results for cases that have also been computed with other CFD codes, as well as have been experimentally investigated. Comparisons are made both with numerical and experimental results.
The first case studied is the steady flow in the Hölleforsen (Turbine-99) draft tube. The OpenFOAM result proved to be comparable with results from all the major CFD tools on the market according to the proceedings from the Turbine-99 III workshop in December 2005 (www.turbine-99.org). An unsteady computation of the flow in the same draft tube has also been made, yielding an unsteady vortex rope with a period of 0.48s. All OpenFOAM draft tube results are similar to results obtained with CFX-5, and the results are close to the experimental results.
The second case studied is the steady flow in the Hölleforsen runner. The computations have been performed both for a single runner blade passage using periodic boundaries, and for the full runner, yielding the same results. In all cases the tip clearance has been included and computations both with and without the runner blade clearance at the hub has been made. The computational results compare well with the experimental results.
All the computations use wall-function grids and turbulence is modelled using the standard k-epsilon model.
IAHR 2006, Yokohama, 2006
Abstract
The objective of this work is to improve numerical predictions of unsteady turbulent flows in the draft tubes of hydraulic power plants. The standard two-equation turbulence models are known to have a strong damping effect on the resolved turbulence in this type of flow. In order to reduce this negative influence of the model, while retaining the usually satisfying near-wall behaviour, a dynamic filtering technique of the turbulent length and time scales is generalised, employed and evaluated. The filter limits the influence of the modeled turbulent length and time scales on the mean flow in regions where unsteadiness can potentially be resolved. The Wilcox (1988) k-omega turbulence model was chosen as basis for the investigations, and the effects of five different filter widths were examined. The original non-filtered model is also evaluated. A swirling flow through a straight axisymmetric diffuser was chosen as a test case and detailed measurements carried out by Clausen et al. were used to validate the numerical results. The influence of the filtering approach on the resolved frequencies and the time averaged solutions were analysed. It is shown that the filtering procedure gives better predictions of the time-averaged velocity field and more information on the large scale unsteadiness.
IAHR 2006, Yokohama, 2006
Abstract
Turbulent swirling flow through a sudden expansion is investigated numerically using Large Eddy Simulation (LES). The flow resembles the flow in a draft tube of a water turbine that is working at part load. The swirling inflow is subject to a strong adverse pressure gradient and the symmetry of the flow breaks down close to the inlet. This gives rise to an oscillating, helicoidal vortex core which in turn creates a highly unsteady and turbulent flow field. In this work, the large-scale turbulent structures are numerically resolved, and detailed information about the flow characteristics is obtained. The oscillating flow is analysed using Fourier transforms of the wall pressure at different downstream locations. The most dominant frequency corresponds to the rotational rate of the precessing vortex core, and it is found that this frequency is constant throughout the domain. The results of two simulations using numerical discretization schemes of different order are compared. It is shown that the frequency of the precessing vortex core is not sensitive to the choice of discretization. However, the lower frequencies of the flow depend to a higher extent on the numerical accuracy. To validate the results, the computed velocities are averaged and compared to experimental data. The agreement is good. The Reynolds stress tensor is also computed and analysed. It is found that large degrees of turbulent anisotropy are found only in the region that is dominated by the oscillating vortex core. Further downstream, the degree of turbulent anisotropy is almost negligible despite the relatively higher level of swirl.
Phys. Fluids 19, 2007
Abstract
This paper analyzes the properties of viscous swirling flow in a pipe. The analysis is based on the time-averaged quasicylindrical Navier-Stokes equations and is applicable to steady, unsteady, and turbulent swirling flow. A method is developed to determine the critical level of swirl (vortex breakdown) for an arbitrary vortex. The method can also be used for an estimation of the radial velocity profile if the other components are given or measured along a single radial line. The quasicylindrical equations are rearranged to yield a single ordinary differential equation for the radial distribution of the radial velocity component. The equation is singular for certain levels of swirl. It is shown that the lowest swirl level at which the equation is singular corresponds exactly to the sufficient condition for axisymmetric vortex breakdown as derived by Wang and Rusak [J. Fluid Mech. 340, 177 (1997)] and Rusak et al. [AIAA J. 36, 1848 (1998)]. In narrow regions around the critical levels of swirl, the solution violates the quasicylindrical assumptions and the flow must undergo a drastic change of structure. The critical swirl level is determined by the sign change of the smallest eigenvalue of the discrete linear operator which relates the radial velocities to effects of viscosity and turbulence. It is shown that neither viscosity nor turbulence directly alters the critical level of swirl. © 2007 American Institute of Physics. [DOI: 10.1063/1.2717724]
Proceedings of the 2nd IAHR International Meeting of the Workgroup on Cavitation and Dynamical Problems in Hydraulic Machinery and Systems, "Polytechnica" University of Timisoara, Romania, October 24-26, 2007. Scientific Bulletin of the "Polytechnica" University of Timisoara, Romania. Transactions on Mechanics, Tom 52(66), Fasciola 6, ISSN 1224 - 6077, pp. 21-34.
Abstract
Cavitation can be modelled with a wide spectrum of methods, ranging from simple potential flow methods to highly resolved multi phase flow simulations. In this work a transport equation for the liquid/vapour volume fraction is integrated into the Implicit Large Eddy Simulation (ILES) equations, giving a highly resolved and time accurate solution strategy. Two mass transfer models, also called cavitation models, are incorporated as source terms to model the transfer of mass from liquid to vapour and back. The mass transfer models used in the present work are inspired by the works of Kunz and Sauer. These two models are based on different physical background, but the resulting equations are relatively similar. A modification of the Sauer mass transfer model is proposed, where the cavitation nuclei distribution is obtained from a separate Lagrangian Particle Tracking (LPT) simulation. Two test cases are used for the validation of the Kunz and Sauer mass transfer models, a two dimensional (2D) NACA0015 hydrofoil and a three dimensional (3D) twisted hydrofoil, the Twist11.
The 2D NACA0015 case is primarily used for testing of parameters, such as the influence of the grid resolution, the mass transfer models and the numerical interpolation schemes. Yet the results show that the computational model captures many of the features seen in the experiments, such as reentrant jets and periodic shedding. The 3D Twist11 case is a very demanding test case with many flow phenomena of interest, such the side entrant jets, which results in a closure at the centerplane, this leads to a cavity that is caught in a hairpin vortex which is transported into the wake and a reentrant jet which cuts of the sheet cavity at the leading edge. These are all features that the models are able to resolve, and the simulations thus give a realistic cavitation pattern. The representation of the side- and reentrant jets are very important to obtain a physical shedding mechanism. If the shedding is precisely represented and the early development of the cavity is correctly modelled, experience and knowledge from earlier cavitation experiments can be used to evaluate the risk of erosion.
Proceedings of the 1st OpenFOAM International Conference, 26-27 November 2007, Beaumont House, Old Windsor, United Kingdom.
Abstract
OpenFOAM has been used successfully at Chalmers for water turbine applications since the beginning of 2005. OpenFOAM has been validated for the flow in a Kaplan water turbine runner and draft tube, and for the swirling unsteady flow in a combustor. The flow in the combustor resembles the flow in a water turbine draft tube (which is a diffuser), with its adverse pressure gradient and unsteady flow features. The results compare well with the experimental results. For the flow in the draft tube the OpenFOAM results are almost identical to those of the CFX-5 CFD code. For the flow in the combustor the OpenFOAM results show the same trend as the results using the Fluent CFD code. OpenFOAM gives similar results as the CALC-PMB in-house CFD code that was developed specifically for water turbine applications (however, no comparisons are shown here).
Many interesting flow features in water turbines are unsteady. There is an interaction between steady and rotating parts of the machine, which should be properly resolved. There are also flow instabilities like the break-up of the vortex after the runner, yielding a highly unsteady flow (here referred to as the \emph{vortex rope}). A CFD code used for water turbine applications should thus be able to include rotor-stator interaction and allow unsteady flow features to appear without numerical damping. OpenFOAM is not yet fully developed for full rotor-stator interaction in water turbines. In the present work a rotating inlet boundary condition is shown, which makes it possible to include guide vane wakes or non-axisymmetry from the spiral casing from a previous simulation of the distributor. The present work evaluates a newly developed filtering technique for the k-omega SST turbulence model. It is shown that the filter is necessary to get unsteady and accurate time averaged results of the flow in the combustor.
The Reynolds numbers in water turbines are high, the geometries are complicated, and the computational grids are usually coarse and skew. It is thus necessary to use models and methods that can give accurate results also under non-ideal conditions.
Proceedings of the 12th International Symposium on Transport Phenomenoa and Dynamics of Rotating Machinery (ISROMAC), Honolulu, Hawaii, February 17-22, 2008.
Abstract
The rotordynamic behaviour of a hydraulic turbine is influenced by fluid-rotor interactions at the turbine runner. In this paper computational fluid dynamics (CFD) is used to numerically predict the rotordynamical excitation forces due to the flow through a hydraulic turbine runner. The simulations are carried out for three diffferent boundary conditions. One axi-symmetric inlet boundary condition, and two axi-periodic boundary conditions. The two latter are obtained from separate simulations of wicket gate and spiral casing flow. It is found that the inlet boundary condition significantly affects the rotordynamical forces and moments.
J. Fluids Eng. -- May 2008 -- Volume 130, Issue 5, 051401 (10 pages)
Abstract
An adaptive low-pass filtering procedure for the modeled turbulent length and time scales is derived and applied to Wilcox's original low Reynolds number k-omega model. It is shown that the method is suitable for complex industrial unsteady flows in cases where full large eddy simulations (LESs) are unfeasible. During the simulation, the modeled length and time scales are compared to what can be potentially be resolved by the computational grid and time step. If the modeled scales are larger than the resolved scales, the resolved scales will replace the modeled scales in the formulation of the eddy viscosity. The filtered k-omega model is implemented in an in-house computational fluid dynamics (CFD) code, and numerical simulations have been made of strongly swirling flow through a sudden expansion. The new model surpasses the original model in predicting unsteady effects and producing accurate time-averaged results. It is shown to be superior to the wall-adapting local eddy-viscosity (WALE) model on the computational grids cosidered here, since the turbulence may not be sufficiently resolved for an accurate LES. Because of the adaptive formulation, the filtered k-omega model has the potential to be successfully used in any engineering case where an LES is unfeasible and a Reynolds (ensemble) averaged Navier-Stokes simulation is insufficient. [DOI: 10.1115/1.2911685]
24th IAHR Symposium on Hydraulic Machinery and Systems, Foz do Iguassu, Brazil, October 27-31, 2008
Abstract
The OpenFOAM CFD toolbox was released as OpenSource December 10, 2004, and since then the number of users throughout the world has increased dramatically. Many industries concerned with turbomachinery (water turbines) are investing a lot of money each year in commercial CFD solvers. The availability of cheap hardware makes it possible to do simulations on a large number of CPUs, which requires many expensive software licenses. There is thus a need for a high quality CFD tool that is cheap, and OpenFOAM is the first tool to meet those demands. OpenFOAM has many of the features that are available in the commercial CFD codes, and due to the OpenSource distribution under the GPL licence it can be used at no cost. There is however a need to develop and maintain some of the features that are specifically needed for turbomachinery applications, and for that reason a turbomachinery Working Group of OpenFOAM users was formed at the second OpenFOAM workshop in Zagreb 2007. The first task of the working group has been to contribute to the set-up of the OpenFOAM-extend project at SourceForge, which is used as a platform for the collaborative effort within the working group, as well as a way to distribute the work to anyone who need to take part of it. The second task of the working group has been to organize a turbomachinery session at the third OpenFOAM workshop in Milano 2008. At that workshop the ERCOFTAC conical diffuser was studied as a validation testcase for OpenFOAM.
The present paper describes the OpenFOAM CFD toolbox, and the features that are of interest to the water turbine community. It will further present the OpenFOAM Turbomachinery Working Group, the ERCOFTAC conical diffuser validation testcase for OpenFOAM, the conclusions from the turbomachinery session of the third OpenFOAM workshop, and the OpenFOAM-extend project at SourceForge.
KEY WORDS: CFD, OpenFOAM, Turbomachinery, Water Turbine, Diffuser, Subversion
24th IAHR Symposium on Hydraulic Machinery and Systems, Foz do Iguassu, Brazil, October 27-31, 2008
Abstract
The present work compares the CFX and OpenFOAM CFD codes with respect to the prediction of the flow in the U9 Kaplan turbine spiral casing, distributor and draft tube. The simulations use similar settings and the same computational grids ~V unstructured wall-function grids with 10.3M cells in the spiral casing and distributor, and 1.04M cells in the draft tube. The results show that the two codes give similar results in the spiral casing and distributor, and almost identical results in the draft tube. Previous studies [1] have shown the same behaviour in the Turbine-99 draft tube, for a block-structured wall-function grid. There are however no previous studies where the flow in a spiral casing and distributor have been studied and compared using the same settings and computational grid in CFX and OpenFOAM.
The next phase of the project consists of comparisons with the results from an on-going experimental investigation.
KEY WORDS: CFD, Water Turbine, Draft Tube, Spiral Casing, Distributor, CFX, OpenFOAM
International Journal of Rotating Machinery, vol. 2009, Article ID 349397, 7 pages, 2009. doi:10.1155/2009/349397
Abstract
The rotordynamic behavior of a hydraulic turbine is influenced by fluid-rotor interactions at the turbine runner. In this paper computational fluid dynamics (CFD) is used to numerically predict the torsional dynamic coefficients due to added polar inertia, damping and stiffness of a Kaplan turbine runner. The simulations are carried out for three operating conditions, one at about 35% load, one at about 60% load (near best effciency) and one at about 70% load.
The runner rotational speed is perturbed with a sinusoidal function with different frequencies in order to estimate the coeffcients of added polar inertia and damping. It is shown that the added coeffcients are dependent of the load and the oscillation frequency of the runner. This affect the system's eigenfrequencies and damping. The eigenfrequency is reduced with up to 65% compared to the eigenfrequency of the mechanical system without the fluid interaction. The contribution to the damping ratio varies between 30-80% depending on the load. Hence, it is important to consider these added coeffcients while carrying out dynamic analysis of the mechanical system.
3rd IAHR International Meeting of the Workgroup on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems, October 14-16, 2009, Brno, Czech Republic
Abstract
The paper presents three-dimensional numerical investigations of the unsteady swirling flow in a conical diffuser with a precessing vortex rope. The helical vortex breakdown, also known as precessing vortex rope in the engineering literature, benefits from a large body of literature aimed either at elucidating the physics of the phenomenon and building mathematical models, or at developing and testing practical solutions to control the causes and/or the effects. In this paper we investigate the unsteady hydrodynamic fields with a well-known precessing vortex rope computed with the FLUENT and OpenFOAM CFD codes. The main goal is to elucidate the physics of the phenomenon. The three-dimensional computational domain corresponds to the test section of a test rig designed and developed at Politehnica University of Timisoara. The same domain and grid with two millions cells is considered in both codes. The boundary conditions and problem setup are presented for each case. The unsteady pressure fluctuations along to the element of the conical diffuser are recorded. The numerical pressure fluctuations are validated against experimental data measured on the wall of the test rig. Consequently, the fundamental frequency and higher harmonics of the vortex rope is determined by a Fourier analysis.
KEYWORDS
unsteady turbulent swirling flow, conical diffuser, precessing vortex rope, numerical simulation
3rd IAHR International Meeting of the Workgroup on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems, October 14-16, 2009, Brno, Czech Republic
Abstract
This work investigates the rotor-stator interaction features of OpenFOAM-1.5-dev, such as frozen rotor and sliding grid. The case studied is the ERCOFTAC Test Case U3: Centrifugal Pump with a Vaned Diffuser, a testcase from the ERCOFTAC Turbomachinery Special Interest Group. The case was presented by Combes at the ERCOFTAC Seminar and Workshop on Turbomachinery Flow Prediction VII, in Aussois, 1999. It is a valid test case for evaluation of rotor-stator interaction features, as detailed experimental data is available. The investigation shows that OpenFOAM gives results that are comparable to the experimental data, in particular for the sliding grid case. The results are less accurate in the frozen rotor simulation due to the improper treatment of the impeller wakes that is part of the frozen rotor formulation. The ERCOFTAC centrifugal pump OpenFOAM case-study was developed as a contribution to the OpenFOAM Turbomachinery Working Group, and was presented and discussed at the Fourth OpenFOAM Workshop in Montreal, 2009. The complete set-up of the case-study is available from the OpenFOAM-extend project at SourceForge, and instructions and comments are available from the OpenFOAM Wiki.
KEYWORDS
CFD, OpenFOAM, Turbomachinery, Frozen rotor, Sliding grid, GGI, ERCOFTAC centrifugal pump
7th International Conference on Multiphase Flow, ICMF 2010, Tampa, USA, May 31-June 4, 2010
Abstract
The performance of the mass transfer cavitation model of Sauer is investigated using a varying nuclei concentration. The Sauer model assumes a uniform nuclei distribution despite measurement of the non-homogeneous nucleus population. Here the nuclei density is studied and a non-homogeneous nuclei distribution in a modified Sauer model is implemented. It is used to study how the increased cavitation nuclei density in regions of low pressure affects the inception of cavitation. The interface between the water and the water vapor is tracked using a volume of fluid method and vaporization and condensation are described by the modified Sauer¿s mass transfer model. The nuclei in the liquid phase are modeled with a Lagrangian Particle Tracking method. The LPT computations yield to a non uniform nuclei distribution which consists of nuclei accumulation close to the leading edge and no nuclei on average in the boundary layer of the hydrofoil. The sensitivity of the modified Sauer model to nuclei distribution is proven. The shape of the sheet cavity and the volume of vapour are affected by the nuclei content.
Proc. 6th World Congress of Biomechanics, Singapore, 1-6 August 2010, p.52, paper SPKA00179-00298
Abstract
V.European Conference on Computational Fluid Dynamics, ECCOMAS CFD 2010, J.C.F. Pereira and A. Sequeira (Eds.), Lisbon, Portugal, 14-17 june 2010
Abstract
Hydroelectric power generation plays an important role in the total electric power generation in Sweden. Almost half of the electric power in Sweden is generated by hydro electric power plants and any modifications and improvements of the system would lead to a significant contribution to the total electric energy production. Two large sources of losses in the electric generators are the thermal and ventilation losses. The electric resistance in the generator system causes heat generation in windings and coils, which decreases the total efficiency of the stator in delivering power and causes material through thermal stresses in components. The generators are thus cooled by air flowing through the rotor and stator. This paper will focus on ventilation of axially air-cooled generators through the stator cooling channels in the stator wall. The name axial suggests that the air movement in the gap between rotor and stator is along the rotors axis of rotation. It is important to have a good understanding of the complicated flow field in the air passages in the generator in order to be able to design the cooling of the system. The air flow is driven by the rotational movement of the rotor and its appended poles, which will act as a fan, into the radially extended stator channels. The air thus cools the stator body and the stator coils. The flow in the generator here is in the present work modeled with a multiple-reference-frame method, which includes source terms for rotation. This ensures that Coriolis effects are taken into account in the simulations. The flow is simulated employing a low-Reynolds number turbulence model where the fluid flow is solved throughout the boundary layer. The computational domain is generated without inlets and outlets so that the volume rate of flow through the generator is determined by the solution, rather than by an imposed inlet volume flow rate. Some parts of the surrounding environment are thus included in the simulation to allow for recirculation of air in the domain. The establishment of the flow depends on the pressure distribution in the domain. The development of the pressure distribution has been validated for the laminar flow between two concentric circular cylinders where the inner cylinder rotates and the outer is at rest. The numerical results for both pressure and velocity distributions have been in agree with analytical results, which will also be presented in the paper.
25th IAHR Symposium on Hydraulic Machinery and Systems, Timisoara, Romania, 2010, IOP Conf. Ser.: Earth Environ. Sci. 12 012056, doi: 10.1088/1755-1315/12/1/012056
Abstract
This work presents numerical results, using OpenFOAM, of the flow in the swirl flow generator test rig developed at Politehnica University of Timisoara, Romania. The work shows results computed by solving the unsteady Reynolds Averaged Navier Stokes equations. The unsteady method couples the rotating and stationary parts using a sliding grid interface based on a GGI formulation. Turbulence is modeled using the standard k-epsilon model, and block structured wall function ICEM-Hexa meshes are used. The numerical results are validated against experimental LDV results, and against designed velocity profiles. The investigation shows that OpenFOAM gives results that are comparable to the experimental and designed profiles. This case study was presented at the 5th OpenFOAM Workshop, held in Gothenburg, Sweden, as a tutorial on how to treat turbomachinery applications in OpenFOAM.
25th IAHR Symposium on Hydraulic Machinery and Systems, Timisoara, Romania, 2010, IOP Conf. Series: Earth and Environmental Science 12 (2010) 012024 doi:10.1088/1755-1315/12/1/012024
Abstract
The present work compares simulations made using the OpenFOAM CFD code with experimental measurements of the flow in the U9 Kaplan turbine model. Comparisons of the velocity profiles in the spiral casing and in the draft tube are presented. The U9 Kaplan turbine prototype located in Porjus and its model, located in Älvkarleby, Sweden, have curved inlet pipes that lead the flow to the spiral casing. Nowadays, this curved pipe and its effect on the flow in the turbine is not taken into account when numerical simulations are performed at design stage. To study the impact of the inlet pipe curvature on the flow in the turbine, and to get a better overview of the flow of the whole system, measurements were made on the 1:3.1 model of the U9 turbine. Previously published measurements were taken at the inlet of the spiral casing and just before the guide vanes, using the laser Doppler anemometry (LDA) technique. In the draft tube, a number of velocity profiles were measured using the LDA techniques. The present work extends the experimental investigation with a horizontal section at the inlet of the draft tube. The experimental results are used to specify the inlet boundary condition for the numerical simulations in the draft tube, and to validate the computational results in both the spiral casing and the draft tube. The numerical simulations were realized using the standard k-e model and a block-structured hexahedral wall function mesh.
International Journal of Fluid Machinery and Systems, Vol. 4, No. 1, January-March 2011, DOI: 10.5293/IJFMS.2011.4.1.199, ISSN (Online): 1882-9554
Abstract
This work presents numerical results, using OpenFOAM, of the flow in the swirl flow generator test rig developed at Politehnica University of Timisoara, Romania. The work shows results computed by solving the unsteady Reynolds Averaged Navier Stokes equations. The unsteady method couples the rotating and stationary parts using a sliding grid interface based on a GGI formulation. Turbulence is modeled using the standard k-epsilon model, and block structured wall function ICEM-Hexa meshes are used. The numerical results are validated against experimental LDV results, and against design velocity profiles. The investigation shows that OpenFOAM gives results that are comparable to the experimental and design profiles. The unsteady pressure fluctuations at four different positions in the draft tube is recorded. A Fourier analysis of the numerical results is compared whit that of the experimental values. The amplitude and frequency predicted by the numerical simulation are comparable to those given by the experimental results, though slightly over estimated.
Keywords: Swirl generator, OpenFOAM, CFD, Validation, Runner, Draft tube, Rotor-Stator Interaction.
IIW Commission XII / SG 212 Intermediate meeting, University West, Trollhättan, Sweden, 21 - 23 March 2011, IIW Doc. XII-2017-11.
Abstract
This study focuses on the simulation of a plasma arc heat source in the context of electric arc welding. The simulation model was implemented in the open source CFD software OpenFOAM-1.6.x, in three space dimensions, coupling thermal fluid mechanics with electromagnetism. Two approaches were considered for calculating the magnetic field: i) the three-dimensional approach, and ii) the so-called axisymmetric approach. The electromagnetic part of the solver was tested against analytic solution for an infinite electric rod. Perfect agreement was obtained. The complete solver was tested against experimental measurements for Gas Tungsten Arc Welding (GTAW) with an axisymmetric configuration. The shielding gas was argon, and the anode and cathode were treated as boundary conditions. The numerical solutions then depend significantly on the approach used for calculating the magnetic field. The so-called axisymmetric approach indeed neglects the radial current density component, mainly resulting in a poor estimation of the arc velocity. Plasma arc simulations were done for various Ar-x%CO2 shielding gas compositions: pure argon ( x =0), pure carbon dioxide ( x =100), and mixtures of these two gases with x =1 and 10% in mole. The simulation results clearly show that the presence of carbon dioxide results in thermal arc constriction, and increased maximum arc temperature and velocity. Various boundary conditions were set on the anode and cathode (using argon as shielding gas) to evaluate their influence on the plasma arc. These conditions, difficult to measure and to estimate a priori, significantly affect the heat source simulation results. Solution of the temperature and electromagnetic fields in the anode and cathode will thus be included in the forthcoming developments.
Keywords: electric arc welding, electric heat source, thermal plasma, magnetic potential, inert gas, active gas, spatial distribution of thermal energy, GTAW, TIG, WIG.
Proceedings from the 4th Swedish Production Symposium, Lund, Sweden, p. 202-211
Abstract
This study focuses on the modeling of a plasma arc heat source in the context of electric arc welding. The model was implemented in the open source CFD software OpenFOAM-1.6.x, coupling thermal fluid mechanics in three dimensions with electro magnetics. Four different approaches were considered for modeling the electromagnetic fields: i) the three-dimensional approach, ii) the two-dimensional axi-symmetric approach, iii) the electric potential formulation, and iv) the magnetic field formulation as described by Ramírez et al. [1]. The underlying assumptions and the differences between these models are described in detail. Models i) to iii) reduce to the same quasi one-dimensional limit for an axi-symmetric configuration with negligible radial current density, contrary to model iv). Models ii) to iv) do not represent the same physics when the radial current density is significant, such as or an electrode with a conical tip. Models i) to iii) were retained for the numerical simulations. The corresponding results were validated against the analytic solution of an infinite electric rod. Perfect agreement was obtained for all the models tested. The results from the coupled solver (thermal fluid mechanics coupled with electromagnetics) were compared with experimental measurements for Gas Tungsten Arc Welding (GTAW). The shielding gas was argon, the arc was short (2mm), the electrode tip was conical, and the configuration was axi-symmetric. The boundary conditions were specified at the anode and cathode surfaces. Models i) and ii) lead to the same results, but not the model iii). Model iii) neglects the radial current density component, resulting in a poor estimation of the magnetic field, and in turn of the arc fluid velocity. The limitations of the coupled solver were investigated changing the gas composition, and using different boundary conditions. The boundary conditions, difficult to measure and to estimate a priori, significantly affect the simulation results.
Keywords: electric arc welding, thermal plasma, short arc, electromagnetic model, electric potential formulation, magnetic field formulation, GTAW.
4-th International Meeting on Cavitation and Dynamic Problems in Hydraulic Machinery and Systems, October, 26-28, 2011, Belgrade, Serbia
Abstract
The actual mass transfer cavitation models are limited by the grid size dependency of the Volume-Of-Fluid method. A new multi-scale approach is developed which can model the presence of bubbles smaller than the grid size. Using this method for simulations of cavitating hydrofoil will lead to a better modelling of the mixture of vapor and liquid in the transition region between the attached cavity and the shedding cloud. The principle of this approach is to complement the VOF method with a two-way coupling Lagrangian particle tracking method. The VOF-LPT coupling model is tested on simplified configurations for the breakup of an attached cavity. The results show that the model successfully displays the formation of small structures and gives a better description of the liquid/gas mixture.
Keywords: numerical simulation, VOF, LPT, multi-scale, cloud cavitation, OpenFOAM.
European Research Community On Flow, Turbulence and Combustion, ETMM9
Abstract
The cooling air flow inside an electric generator has been numerically simulated and validated with experimental measurements. The numerical studies are performed using OpenFOAM in a quasi-steady mode at three rotor speeds. The numerical and experimental results show similar flow distributions.
Keywords: OpenFOAM Cooling Turbulence Generator Experiment Computation
International Journal of Rotating Machinery, Volume 2013 (2013), Article ID 961580, 14 pages, http://dx.doi.org/10.1155/2013/961580
Abstract
Computational fluid dynamics (CFD) analyses were made to study the unsteady three-dimensional turbulence in the ERCOFTAC centrifugal pump test case. The simulations were carried out using the OpenFOAM Open Source CFD software. The test case consists of an unshrouded centrifugal impeller with seven blades and a radial vaned diffuser with 12 vanes. A large number of measurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numerical methods. Results of steady and unsteady calculations of the flow in the pump are compared with the experimental ones, and four different turbulent models are analyzed. The steady simulation uses the frozen rotor concept, while the unsteady simulation uses a fully resolved sliding grid approach. The comparisons show that the unsteady numerical results accurately predict the unsteadiness of the flow, demonstrating the validity and applicability of that methodology for unsteady incompressible turbomachinery flow computations. The steady approach is less accurate, with an unphysical advection of the impeller wakes, but accurate enough for a crude approximation. The different turbulence models predict the flow at the same level of accuracy, with slightly different results.
Abstract
The dynamics of individual flexible fibers in a turbulent flow field have been analyzed, varying their initial position, density and length. A particle-level fiber model has been integrated into a general-purpose, open source computational fluid dynamics code. The fibers are modeled as chains of cylindrical segments connected by ball and socket joints. The equations of motion of the fibers contain the inertia of the segments, the contributions from hydrodynamic forces and torques, and the connectivity forces at the joints. Direct numerical simulation of the incompressible Navier-Stokes equations is used to describe the fluid flow in a plane channel, and a one-way coupling is considered between the fibers and the fluid phase. We investigate the translational motion of fibers by considering the mean square displacement of their trajectories. We find that the fiber motion is primarily governed by velocity correlations of the flow fluctuations. In addition, we show that there is a clear tendency of the thread-like fibers to evolve into complex geometrical configurations in a turbulent flow field, in fashion similar to random conformations of polymer strands subjected to thermal fluctuations in a suspension. Finally, we show that fiber inertia has a significant impact on reorientation timescales of fibers suspended in a turbulent flow field.
Applied Energy, Volume 114, February 2014, Pages 644-653
Abstract
The need for electric power is continuously increasing. The power output of existing electric generators is forced to its limit, and the new intermittent electric energy sources increase the variations of the operating conditions of the electric generators in the power system. This requires better cooling of the heat that is generated by the electric losses in generators. New experimental and numerical techniques need to be developed and validated, to increase the knowledge of the cooling processes and to improve the accuracy of the design tools. The present work focuses on the flow of air through electric generators, as a necessary and important first step towards future accurate and detailed convective heat transfer analysis. A half-scale model of an electric generator is designed and manufactured specifically for detailed experimental and numerical studies of the flow of cooling air through the machine. The model is slightly simplified compared to the original geometry, to benefit from the use of geometry parameterization, and with numerical mesh quality in mind already at the design of the experimental set-up. Special care is taken to provide optical access for accurate and detailed Particle Image Velocimetry (PIV) measurements inside the machine. The experimental measurements include PIV measurements at the inlet and inside the machine, and total pressure measurements at the outlet of the stator channels. Computational Fluid Dynamics (CFD) simulations are performed using two approaches. In one approach the inlet flow rate is specified from the experimental data, as is commonly done in the literature. In the other approach the flow rate is determined from the numerical simulation, independently of the experimental results, yielding predictions differing by 2-7% compared to the experimentally estimated values. The results of both approaches capture the experimental flow details to a high level of accuracy. Mesh sensitivity studies highlight the need of a specific resolution of the baffle edges.
Cite: Roos H, et al., Displacement Forces in Iliac Landing Zones and Stent Graft Interconnections in Endovascular Aortic Repair: An Experimental Study, European Journal of Vascular and Endovascular Surgery (2014), http://dx.doi.org/10.1016/j.ejvs.2013.11.015
Abstract
Objectives: Stent graft migration influences the long-term durability of endovascular aortic repair. Flow-induced
displacement forces acting on the attachment zones may contribute to migration. Proximal fixation of aortic stent
grafts has been improved by using hooks, while distal fixation and stent graft interconnections depend on selfexpansion
forces only. We hypothesized that flow-induced displacement forces would be significant at the distal
end, and would correlate with graft movements.
Methods: As part of an experimental study, an iliac limb stent graft was inserted in a pulsatile flow model similar
to aortic in vivo conditions, and fixedemounted at its proximal and distal ends to strain gauge load cells. Peak
displacement forces at both ends and pulsatile graft movement were recorded at different graft angulations (0-
90degrees), perfusion pressures (145/80, 170/90, or 195/100 mmHg), and stroke frequencies (60-100 b.p.m.).
Results: Flow-induced forces were of the same magnitude at the proximal and distal end of the stent graft (peak
1.8 N). Both the forces and graft movement increased with angulation and perfusion pressure, but not with
stroke rate. Graft movement reached a maximum of 0.29 - 0.01 mm per stroke despite fixed ends. There were
strong correlations between proximal and distal displacement forces (r = 0.97, p < .001), and between
displacement forces and graft movement (r = 0.98, p < .001).
Conclusions: Pulsatile flow through a tubular untapered stent graft causes forces of similar magnitude at both
ends and induces pulsatile graft movements in its unsupported mid-section. Peak forces are close to those
previously reported to be required to extract a stent graft. The forces and movements increase with increasing
graft angulation and perfusion pressure. Improved anchoring of the distal end of stent grafts may be considered.
Copyright 2013 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved.
Article history: Received 6 August 2013, Accepted 29 November 2013, Available online XXX
Keywords: Stent graft, EVAR, Blood flow, Displacement force, Aortic aneurysm, Angulation
Applied Energy 124 (2014) 223–230
Abstract
A fully predictive computational fluid dynamics approach is assessed for the flow of cooling air in an axially cooled electric generator. The flow is driven solely by the rotation of the rotor, as in the real application. A part of the space outside the generator is included in the computational domain to allow for the flow of air into and out of the machine. This yields a flow prediction that is determined without the input of any experimental data. Two different choices of 'surrounding' outer boundary conditions are studied, and the mesh sensitivity is discussed.
The numerically predicted flow is compared with experimental data. Flow visualizations are performed at the inlet. The inlet velocity distribution is determined using 5-hole and total pressure probes. The outlet velocity distribution is determined using a total pressure rake.
It is found that the numerical approach qualitatively, and to a large extent quantitatively, predicts the same velocity distributions as in the experiment. The numerically predicted flow rates are however lower than that estimated from the experimental data. The differences are considered small, given the many uncertainties in both the numerical and experimental studies, and that they are performed completely independently.
Swedish Production Symposium 2014, Gothenburg, Sweden
Abstract
Modelling of the arc in electric arc welding is significant to achieve a better process understanding, thus gain better weld quality and a more efficient production process. It requires knowing the conditions at the surfaces of the anode and cathode. These conditions are very difficult to set from measurements and should be calculated. This requires modelling the complex physics of the electrode layer coupling electrode and arc. This paper presents a selfconsistent electrode layer model that 1) is suited to welding applications, 2) accounts for the known physics taking place, and 3) satisfies the basic conservation requirements. The model is tested for different conditions. Its potentiality for welding applications is shown through calculations coupling plasma arc, electrode and cathode layer models. The calculations are done for both tungsten and thoriated tungsten electrode.
Keywords: thermal plasma, arc welding, electrode layer, sheath, electrode surface temperature, numerical simulation, OpenFOAM.
5h Symposium on Hybrid RANS-LES Methods, 19-21 March 2014
Abstract
A highly swirling turbulent flow engendered by the rotor-stator interaction of a swirl generator is investigated using LES and DES. The delayed DES Spalart-Allmaras (DDES-SA), improved DDES-SA, shear stress transport DDES, and a dynamic k-equation LES are studied. A mesh sensitivity study is performed on the hybrid methods, including the ability of capturing the details of the flow field. It is shown that all methods are capable of predicting the large-scale flow features, e.g. the vortex breakdown and the corresponding on-axis recirculation region. It is also shown that all hybrid methods capture most of the small-scale coherent structures, even with a relatively coarse mesh resolution. The various shielding functions of the hybrid methods are analyzed, distinguishing the location of the transition between RANS and LES mode.
27th IAHR Symposium on Hydraulic Machinery and Systems
Abstract
The Reynolds-averaged Navier-Stokes equations with the RNG k-ε turbulence model closure are utilized to simulate the unsteady turbulent flow throughout the whole flow passage of the U9 Kaplan turbine model. The U9 Kaplan turbine model comprises 20 stationary guide vanes and 6 rotating blades (696.3 RPM), working at best efficiency load (0.71 m3/s). The studied test case is the 1:3.1 scale model of the U9 Kaplan turbine prototype. The computations are conducted using a general finite volume method, using the OpenFOAM CFD code. A dynamic mesh is used together with a sliding GGI interface to include the effect of the rotating runner. The clearance is included in the guide vane. The hub and tip clearances are also included in the runner. An analysis is conducted of the unsteady behavior of the flow field, the pressure fluctuation in the draft tube, and the coherent structures of the flow. The tangential and axial velocity distributions at three sections in the draft tube are compared against LDV measurements. The numerical result is in reasonable agreement with the experimental data, and the important flow physics close to the hub in the draft tube is captured. The hub and tip vortices and an on-axis forced vortex are captured. The numerical results show that the frequency of the forced vortex is 1/5 of the runner rotation.
27th IAHR Symposium on Hydraulic Machinery and Systems
Abstract
27th IAHR Symposium on Hydraulic Machinery and Systems
Abstract
27th IAHR Symposium on Hydraulic Machinery and Systems
Abstract
Accepted for publication in Journal of Non-Newtonian Fluid Mechanics
Abstract
Particle-level simulations are used to study the rheology of monodispersed suspensions of rigid and flexible fibers in a creeping shear flow of a Newtonian fluid. We also investigate the influence of different equilibrium shapes (straight and curved) of the fibers on the behavior of the suspension. A parametric study of the impacts of fiber flexural rigidity and morphology on rheology quantifies the effects of these realistic fiber features on the experimentally accessible rheological properties. A fiber is modeled as a chain of rigid cylindrical segments, interacting through a two-way coupling with the fluid described by the incompressible three-dimensional Navier--Stokes equations. The initial fiber configuration is in the flow--gradient plane. We show that, when the shear rate is increased, straight flexible fibers undergo a buckling transition, leading to a development of finite first and second normal stress differences and a reduction of the viscosity. These effects, triggered by shape fluctuations, are opposite the effects induced by the curvature of stiff, curved fibers, for which the viscosity increases with the curvature of the fiber. The analysis of the orbital drift of fibers initially directed outside the flow--gradient plane provides an estimate for the time-scale within the predicted rheological behavior is valid. The information obtained in this work can be used in the experimental characterization of fiber morphology and mechanics through rheology.
Proceedings of the ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting and 12th International Conference on Nanochannels, Microchannels and Minichannels Modeling and Simulations, FEDSM2014, August 3-7, 2014 Chicago, Illinois, USA
Abstract
A particle-level rigid fiber model is used to study flocculation in an asymmetric planar diffuser with a turbulent Newtonian fluid flow, resembling one stage in dry-forming process of pulp mats. The fibers are modeled as chains of rigid cylindrical segments. The equations of motion incorporate hydrodynamic forces and torques from the interaction with the fluid, and the fiber inertia is taken into account. The flow is governed by the Reynolds-averaged NavierStokes equations with the standard k-omega turbulence model. A one-way coupling between the fibers and the flow is considered. A stochastic model is employed for the flow fluctuations to capture the fiber dispersion. The fibers are assumed to interact through short-range attractive forces, causing them to interlock as the fiber-fiber contacts occur during the flow. It is found that the formation of fiber flocs is driven by both the turbulence-induced dispersion and the gradient of the averaged flow field.
Journal of Non-Newtonian Fluid Mechanics
Abstract
Particle-level simulations are used to study the rheology of monodispersed suspensions of rigid and flexible fibers in a creeping, simple shear flow of a Newtonian fluid. We also investigate the influence of different equilibrium shapes (straight and curved) of the fibers on the behavior of the suspension. A parametric study of the impacts of fiber flexural rigidity and morphology on rheology quantifies the effects of these realistic fiber features on the experimentally accessible rheological properties. A fiber is modeled as a chain of rigid cylindrical segments, interacting through a two-way coupling with the fluid described by the incompressible three-dimensional Navier--Stokes equations. The initial fiber configuration is in the flow--gradient plane. We show that, when the shear rate is increased, straight flexible fibers undergo a buckling transition, leading to the development of finite first and second normal stress differences and a reduction of the viscosity. These effects, triggered by shape fluctuations, are dissimilar to the effects induced by the curvature of stiff, curved fibers, for which the viscosity increases with the curvature of the fiber. An analysis of the orbital drift of fibers initially oriented at an angle to the flow--gradient plane provides an estimate for the time-scale within which the prediction of the rheological behavior is valid. The information obtained in this work can be used in the experimental characterization of fiber morphology and mechanics through rheology.
1st Francis-99 Workshop, Trondheim, Norway, 2014
Abstract
This work investigates the flow in the scale model of the high-head Tokke Francis turbine at part load, best effciency point and high load, as a contribution to the first Francis-99 workshop. The work is based on the FOAM-extend CFD software, which is a recent fork of the OpenFOAM CFD software that contains new features for simulations in rotating machinery. Steady-state mixing plane RANS simulations are conducted, with an inlet before the guide vanes and an outlet after the draft tube. Different variants of the k-epsilon and k-omega turbulence models are used and a linear explicit algebraic Reynolds stress model is implemented. Sliding grid URANS simulations, using a general grid interface coupling, are performed including the entire turbine geometry, from the inlet to the spiral casing to the outlet of the draft tube. For the unsteady simulations, the k-omega SSTF model is implemented and used in addition to the standard k-omega model. Both the steady and unsteady simulations give good predictions of the pressure distribution in the turbine compared to the experimental results. The velocity profiles at the runner outlet are well predicted at off-design conditions. A strong swirl is however obtained at best effciency point, which is not observed in the experiments. While the steady-state simulations strongly overestimate the effciency, the unsteady simulations give good predictions at best efficiency point (error of 1:16%) with larger errors at part load (10:67%) and high load (2:72%). Through the use of Fourier decomposition, the pressure fluctuations in the turbine are analysed, and the main rotor-stator interaction frequencies are predicted correctly at all operating conditions.
conference
Abstract
| LICENTIATE THESES |
Analytical and numerical investigations of steady and unsteady turbulent swirling flow in diffusers
Walter Gyllenram, Thesis for the degree of licentiate of engineering in thermo and fluid dynamics, 2006:05, Div. of Thermo and Fluid Dynamics, Chalmers University of Technology, Gothenburg.
Abstract
Swirling flows are found in many technical applications, e.g. turbines, pumps, fans, compressors and combustors. The objective of the present work is to acquire an understanding of the physics of swirling ow in general and unsteady swirling ow in draft tubes of water turbines in particular. Analytical studies of axisymmetric swirling ow were carried out using a quasi-cylindrical approximation of the Navier-Stokes equations. It is shown that there are no quasi-cylindrical solutions to the Navier-Stokes equations for certain critical levels of swirl. It is argued that this property of the equations is related to a vortex breakdown phenomenon. In draft tubes of hydraulic power plants, the vortex breakdown phenomenon gives rise to a highly unsteady, oscillating pressure eld that can endanger the machine. Numerical threedimensional and unsteady simulations of swirling ows in simplied draft tube geometries were carried out to investigate this dynamic behaviour. The numerical methods include both LES (large eddy simulations) and RANS (Reynolds averaged Navier-Stokes) simulations. An LES is not an option for a full-scale draft tube simulation but provides valuable information for simplied cases. The RANS simulations in combination with the standard two-equation turbulence models are more applicable for industrial purposes but do not provide enough information about the unsteadiness of the ow. A dynamic ltering procedure of the turbulent length and time scales is generalised, employed and evaluated in order to remedy this shortcoming in the two-equation models. It is shown that the ltering procedure can yield solutions that contain more information about the ow dynamics as well as better time-averaged results compared to an ordinary RANS simulation.
Plasma Arc Welding Simulation with OpenFOAM
(slides)
Margarita Sass-Tisovskaya, Thesis for the degree of licentiate of engineering in thermo and fluid dynamics, 2009:10, Div. of Thermo and Fluid Dynamics, Chalmers University of Technology, Gothenburg.
Abstract
A simulation tool that is valid within the field of tandem arc welding(unsteady, three dimensional thermal plasma flow) has been developed,based on the open source CFD package OpenFOAM. The validation of the electromagnetic part of the solver has been done separately using a problem with a known solution. A good agreement between the numerical and analytical solutions was obtained. Different boundary conditions on the magnetic potential vector have been tested. Based on these tests, the appropriate boundary conditions were chosen for the case representing a transferred arc configuration. The complete simulation tool was validated using a tungsten inert gas single arc problem. Two representations of the magnetic field have been tested, based on the electric and magnetic potentials, respectively. Qualitatively, both approaches agreed well with the results found in the literature. However, quantitatively a deviation in the results was observed in the near cathode region.
Numerical Investigations of Incompressible Turbomachinery Applications using OpenFOAM
Olivier Petit, Thesis for the degree of licentiate of engineering in thermo and fluid dynamics, 2010:02, Div. of Applied Mechanics, Chalmers University of Technology, Gothenburg.
Abstract
Swirling flow and unsteady phenomena are common in technical applications, such as turbines, pumps and compressors. The objective of this work is to get a good understanding of the turbulent flow features inside such applications, and to validate the computational techniques used for such applications.
Because of the complexity of the turbulent flow, approximations are made when solving the flow equations in the computational domain. Depending on the level of the approximations, the level of accuracy and detail in the predicted flow will vary. To validate the assumptions used in the simulations and to get a good prediction of the flow, the computational technique as well as the CFD code must thus be validated against detailed measurements. The present work aims at getting a good understanding of the turbulent flow in the U9 Kaplan turbine model, using the OpenFOAM CFD code. Detailed measurements are used to validate the computed turbulent flow features.
Two methods are used in this present work to predict the interaction between rotating and stationary parts of the machines. The steady-state method coupled with the frozen rotor approach solves the time-averaged Reynolds Averaged Navier Stokes equations, while the unsteady method with the sliding grid approach solves the same equations taking the time dimension into account. To validate the two different computational techniques, comparisons between computational results and detailed measurements for two different case studies are performed: the ERCOFTAC centrifugal pump, and a swirl generator test rig. Good agreement is found between numerical and experimental results.
Eulerian and Lagrangian cavitation related simulations using OpenFOAM
Aurelia Vallier, Thesis for the degree of licentiate of engineering, 2010, Div. of Fluid Mechanics, Department of Energy Sciences, Lund University.
Håkan Nilsson co-supervisor
Abstract
The overall purpose of this work is to investigate and improve the numerical models which are suitable for modeling cavitation inception and development on a hydrofoil.
Cavitation leads to the formation of bubbles of a large range of sizes, from nuclei (microscopic gas bubbles) to large cloud of vapor. The large bubbles can be modeled using the Volume of Fluid model. Indeed this method is adapted to the simulation of attached cavitation because it can handle accuratly the interface when it undergoes distortion and break-up. The first step is to investigate the perfomance of the VOF method implemented in OpenFOAM, for non cavitating conditions (i.e. without mass transfer due to evaporation and condensation). Numerical simulations are performed for deformable air bubbles in a straight channel. Bubble features such as aspect ratio, velocity and path are compared against available experimental data and an in-house code.
One limitation of the mass transfer models developed recently is their assumption of constant nuclei concentration. Lagrangian particle tracking simulations are performed and predict a non homogeneous distribution of nuclei. Taking into account the real nuclei content of the water may improve the accuracy of the numerical simulations. Therefore a mass transfer model was modified to include this non homogeneity and used to study how a non uniform nuclei distribution affects the inception and development of attached sheet cavities.
CFD of Air Flow in Hydro Power Generators
Slides
Pirooz Moradnia, Thesis for the degree of licentiate of engineering in thermo and fluid dynamics, 2010:11, Div. of Applied Mechanics, Chalmers University of Technology, Gothenburg.
Abstract
The air flow through a generator has been numerically investigated with different rotor and stator designs to give a better understanding of the flow for cooling purposes. A simple rotor design has been chosen to start with, and modified through a set of changes, where stepwise modifications have been imposed to the design of the rotor and the stator. The flow properties for all cases have been compared to each other to see the effect of each parameter change on the flow inside the machine.
The flow is predicted with the OpenFOAMsolverMRFSimpleFOAM, which uses the Frozen Rotor concept. This means that there is no actual mesh movement in this study, but instead, the rotating regions in the domain are provided with source terms that account for rotation.
The choice of the turbulence model for solving the air flow in the generator was based on a study of the turbulence models and validation test cases. All incompressible RAS turbulence models in OpenFOAM- 1.5.x were studied and the implementations were compared to the original models. Many of the mentioned turbulence models were tested on a backward-facing step test case. The numerical results were compared to the experimental data and the most appropriate turbulence model was chosen. Details on turbulence model studies are discussed in Appendix A. A laminar Couette flow between two concentric cylinders was run and the numerical velocity and pressure distributions between the cylinders were compared to the analytical results. More details on the validation test cases are found in Appendix B.
Keywords: CFD, Generator, OpenFOAM, Launder-Sharma k-epsilon ,MultipleReferenceFrame
Implementation of a flexible fiber model in a general purpose CFD code
Jelena Andric, Thesis for the degree of Licentiate of Engineering in Thermo and Fluid Dynamics, Dept. of Applied Mechanics, Chalmers University of Technology, Gothenburg.
Modelling of Electric Arc Welding: arc-electrode coupling
Alireza Javidi Shirvan, Thesis for the degree of Licentiate of Engineering in Thermo and Fluid Dynamics, Dept. of Applied Mechanics, Chalmers University of Technology, Gothenburg.
Time-accurate Turbulence Modeling of Swirling Flow for Hydropower Application
Ardalan Javadi, Thesis for the degree of Licentiate of Engineering in Thermo and Fluid Dynamics, Dept. of Applied Mechanics, Chalmers University of Technology, Gothenburg.
| PHD THESES |
Analytical and Numerical Studies of Internal Swirling Flows
Walter Gyllenram
(Only the summary, the papers can be found above)
(errata)
(slides)
Walter Gyllenram, Thesis for the degree of Doctor of Philosophy in Thermo and Fluid Dynamics, Div. of Thermo and Fluid Dynamics, Chalmers University of Technology, Gothenburg.
Abstract
Swirling flows are common in technical applications, e.g. turbines, pumps, fans, compressors and combustors. The objectives of the present work are to acquire an understanding of the physics of swirling flow in general and unsteady swirling flow in draft tubes of hydro turbines in particular, and to find a simulation method suitable for industrial purposes.
An analysis was made of the quasi-cylindrical approximation of the Navier-Stokes equations. The analysis shows that there are no quasi-cylindrical solutions at certain critical levels of swirl. Furthermore, it is shown that this property of the equations is connected to the vortex breakdown phenomenon, i.e. the sudden change of flow structure often observed in swirling flow. In draft tubes in hydraulic power plants, a vortex breakdown gives rise to a precessing vortex core that induces a temporally periodic load on the machine, which in turn causes bearing wear and increases the risk of fatigue failure.
An industrially applicable hybrid LES/RANS method was generalized and employed. The hybrid method is based on a dynamic filtering procedure of the turbulent length and time scales obtained from an eddy-viscosity RANS turbulence model. The method has been used for detailed investigations of the dynamic behaviour of swirling flows through a sudden expansion and a hydro turbine draft tube. It is shown that the filtering procedure yields solutions that contain accurate unsteady information. In addition, the time-averaged results obtained using the filtered model are significantly better than those obtained using other hybrid methods and unsteady RANS simulations.
Keywords: Swirling flow, vortex, draft tube, hydro turbine, LES, RANS, filter, turbulence.
Towards Full Predictions of the Unsteady Incompressible Flow in Rotating Machines, Using OpenFOAM
Olivier Petit
(slides)
Olivier Petit, Thesis for the degree of Doctor of Philosophy in Thermo and Fluid Dynamics, Dept. of Applied Mechanics, Chalmers University of Technology, Gothenburg.
Abstract
The main objective of the present work is to validate methodologies for accurate numerical predictions of the incompressible flow of water in the U9 Kaplan turbine model. The term prediction implies that the use of detailed experimental data for boundary conditions should be avoided, and that all important features of the studied case should be included. That includes specifying boundary conditions at locations where the flow conditions can be easily estimated, and where reasonable variations in those estimations do not significantly affect the flow prediction. As an example, the U9 Kaplan turbine model has a sharply bent inlet pipe, and it is here argued that the secondary flow from that should be taken into account by including the pipe in the simulation. In the case of rotating machines, such as the U9 Kaplan turbine model, the interaction between rotating and stationary components (rotor-stator interaction) is a feature that must be included in the simulations.
Three highly relevant well-documented cases have been used in the present work, the ERCOFTAC Centrifugal Pump, the Timisoara Swirl Generator and the U9 Kaplan turbine model. All three cases include rotor-stator interaction. The latter, being the main goal of the studies, has just recently been studied experimentally and is a computationally demanding case. Thus, the former two cases were used while validating the new implementations and evaluating the numerical settings, until the results were reliable and efficient. Two rotor-stator interaction methods were investigated, the steady-state frozen-rotor approach, and the unsteady sliding grid approach, and the results from four turbulence models were compared.
The results show that both approaches can be used to couple the rotating and stationary parts of the domain. However, the frozen rotor yields an unphysical advection of the runner wakes, and such results should only be used for a first estimation or as initial conditions for full unsteady sliding grid simulations. The predictions compare very well with the experimental results, and the main differences can be explained by the geometrical simplifications that were made. The four turbulence models behave similarly, with a minor preference for different models in the different cases.
The present work is done using the OpenFOAM OpenSource CFD toolbox. The code is chosen to facilitate an OpenSource distribution of the developments, to be shared in the scientific community, and to be directly useful in industry. It was not possible to achieve the results presented here with OpenFOAM before the start of the present work, which has significantly contributed to the validation of, and trust in, the new implementations.
Keywords: OpenFOAM, CFD, Kaplan Turbine, Hydro Power, Sliding Grid, Turbulent Flow
Prediction of Cooling Air Flow in Electric Generators
(only the summary in the link)
Pirooz Moradnia
Thesis for the degree of Doctor of Philosophy in Thermo and Fluid Dynamics, Div. of Thermo and Fluid Dynamics, Chalmers University of Technology, Gothenburg.
Abstract
The cooling air flow in hydro power electric generators is investigated experimentally and numerically. A fully predictive numerical approach is presented and validated, in which the inlet and outlet boundaries are eliminated from the computational domain. Instead, a part of the space outside the machine is included in the computational domain, allowing for recirculation of the cooling air. The predicted flow is therefore driven solely by the rotation of the rotating parts of the generator. In this way, the predicted flow field is independent of any experimental data at the inlet, and is determined completely by the solution. Using the fully predictive approach, a number of parametric numerical studies are performed on the rotor and stator geometries. The effect of adding geometrical details to the rotor and stator are investigated, and stator baffles and rotor fan blades are concluded to increase the volume flow rate through the machine. The volume flow rate through the machine is found to vary linearly with the rotor rotational speed, while the required rotor axial power increases cubically with the rotor rotational speed. The numerical results are validated against experimental measurements in a real electric generator. Flow visualizations, and 5-hole probe and total pressure measurements are performed. A comparison of the numerical results and the experimental data reveals a good qualitative prediction of the flow by the fully predictive numerical approach. The sensitivity of the numerical results to different choices of inlet boundary conditions is also investigated. The level of detail in the boundary conditions proves to play an important role in predicting correct flow features. A half-scale laboratory model, based on the above studied electric generator, is specifically designed and manufactured for experimental studies of the cooling air flow. The measurement accuracy in the half-scale model is significantly improved compared to that in the real generator. The model is provided with static pressure holes and optical access for flow measurements using Particle Image Velocimetry (PIV). The fully predictive numerical approach is shown to yield quantitatively similar results as the experimental flow measurements. The numerical simulations are also performed with inlet and outlet boundary conditions, by specifying the inlet volume flow rates from the experimental measurements. The results of the fully predictive numerical approach are shown to agree better with the experimental data, than those of the simulations with inlet and outlet boundary conditions.
Keywords: CFD, Electric Generator, Multiple Reference Frame, Flow Prediction, OpenFOAM, Experimental Measurements, PIV, Total Pressure Measurements, 5-hole Pressure Probe Measurements
Simulations of cavitation - from the large vapour structures to the small bubble dynamics
Aurelia Vallier
Abstract
Very few people around us know the meaning of the word cavitation, except from those who saw the movie The Hunt for Red October and can relate cavitation to Sean Connery in a submarine. Some of them know that it corresponds to the formation of bubbles, due to a pressure drop, and causes erosion and noise. However, cavitation is much more complex. A large amount of research work has been done over the last thirty years in order to improve the understanding of the interactions between the various physical processes involved. The present work aims at gaining more knowledge about cavitation in water turbines. Some of the properties of cavitation at a water turbine runner blade are similar to those at a hydrofoil in a water test tunnel. Therefore, the overall purpose of this work is to improve the numerical models for cavitation inception and development on a hydrofoil. The focus of this thesis lies on numerical methodologies that include the broad range of cavity sizes, using appropriate models for each specific phenomenon. The smallest bubbles, called nuclei, are tracked in the flow with the Discrete Bubble Model, and their dynamics is resolved with the Rayleigh-Plesset equation. This approach can predict how the nuclei are transported over a hydrofoil to regions of low static pressure, where they grow and either collapse or contribute to the formation of large-scale vapour cavities. The large non-spherical structures are commonly modelled using the Volume-Of-Fluid method together with a mass transfer model for vaporisation and condensation. This approach predicts the development of the vapour cavity, such as its breakup and the shedding process observed experimentally in the context of cavitating hydrofoils. The present work implements the above-mentioned models in the OpenFOAM C++ library, and performs simulations to assess the performance of the models. A new multiscale model is developed, implemented and used on a cavitating hydrofoil. The multi-scale model includes both the small spherical bubbles, the large non-spherical vapour structures, and the transition between those regimes.
Numerical modeling of air-fiber flows
Jelena Andric
Abstract
The dynamics of fiber suspensions are of great importance in applications such as the dry-forming process of pulp mats for use in hygiene products. In this forming process, fibers are transported in flowing air. The fibers interact with the fluid, and may interact with each other and interlock in flocs. The characteristics of the suspension structure are essential for the design and optimization of the forming process, and for improving the quality of the final products. Particularly, it is desired to achieve a uniform fiber distribution in the pulp mats. Thus, it is of high interest to develop tools, which can be used to perform comprehensive studies of the complex phenomenon of fiber suspension flows. This work is concerned with numerical analysis of fiber suspensions, related to the mat-forming process. For that purpose, a particle-level fiber model has been implemented into an open source computational fluid dynamics (CFD) code. A fiber is modeled as a chain of rigid cylindrical segments. The segments interact with the flow through hydrodynamic drag forces, and may interact with each other through short-range attractive forces. The segments are tracked individually using Lagrangian particle tracking (LPT). The implemented model comprises two alternatives, the flexible and the rigid fiber model, respectively. The equations of motion of a flexible fiber represent the application of Euler's second laws for rigid body motion for the fiber segments. The flexible fiber model takes into account all the degrees of freedom necessary to realistically reproduce the fiber dynamics. Connectivity forces act between the adjacent fiber segments to ensure the fiber integrity. The rigid fiber model keeps the relative orientation between the segments fixed. The equations of motion are formulated for the fiber as a whole, while the hydrodynamic contributions are taken into account from the individual segments. The fiber inertia is taken into account in both alternatives of the model. The fiber model has been coupled with imposed flow fields, or with flow fields computed by the CFD solvers. The behavior of the implemented model is compared with analytical and experimental results available in the literature. The simulation results show that the model correctly predicts the dynamics of isolated rigid and flexible fibers in creeping shear flow. The model is used to study the dynamics of flexible and rigid fibers in high Reynolds number flows and in geometries that are representative for the mat-forming process. The effects of fiber properties, such as fiber inertia and fiber length are analyzed. Simulations are carried out to investigate the rheology of suspensions of flexible and curved fibers in creeping shear flow of a Newtonian fluid. The effects of fiber flexibility and fiber curvature on the specific viscosity and the normal stress differences are examined. Finally, aggregation of rod-like fibers is investigated in a turbulent flow of an asymmetric planar diffuser. The influences of the average flow gradient, the fiber inertia and the turbulence dispersion on the aggregation rate are analyzed. The study identifies a darting fiber motion as a mechanism that significantly enhances fiber collisions and aggregation.
| MASTER THESES |
Modeling of Swirling Flow in a Conical Diffuser
Walter Gyllenram
Abstract
This work aims at getting a better understanding of the turbulent swirling flow in a conical diffuser, which represents a highly simplified draft tube of a water turbine. The numerical 3D (U)RANS investigations are quantitatively compared to experimental data. Qualitative comparison with experimental visualizations and computations of similar flows are also made, and strong similarities to confined swirling flow have been found. Converging/diverging smearlines at the walls reveal a very complex boundary layer and counter-rotating vortex structures are found at the diffuser exit. The solutions to the Reynolds averaged Navier-Stokes equations for the studied cases are asymmetric. The asymmetry of the mean flow solution is originating from instable properties of the symmetric mode, and the disturbance that triggers the instability is proven to be imperfections of the CAD-geometry.
There are some discrepancies regarding the agreements with experimental data, partly reminiscent of the nature of the (k-omega) turbulence model that was used in this work. The origins of turbulent anisotropy are theoretically examined as well as the weaknesses of the Boussinesq assumption, which constitutes an important part of the chosen turbulence model.
Also included are a discussion concerning the origin of the turbulent anisotropy and aspects of the filtered (LES) and the averaged (RANS) equations.
Abstract
Volvo Powertrain AB, a part of Volvo Group, uses simulations to develop new diesel engines in a more cost effective way. For every new engine generation there are tougher demands regarding engine power, emission demands and fuel consumption. These demands affect the oil system by adding more thermal energy. The areas where oil mainly receives more thermal energy are in bearings, which are affected by greater forces, and piston cooling, because pistons need additional cooling due to higher combustion temperatures.
The aim of this work is, by using Flowmaster2, to simulate the oil system of the current 16-litre diesel engine to estimate the heat rejection need in the oil cooler. This model is then used to evaluate the concepts that exist as a solution for greater cooling demand in future engines. This report contains also a description of the oil systems function and its components.
The concepts that have been evaluated are:
Cross-flow - alternative solution of the existing engine
Counter-flow - concept with counter-flow oil cooler
Aux-cooler - an extra oil cooler connected in series with the oil system, cross-flow
Aux-cooler parallel connected - an extra oil cooler parallel connected with the system
The simulation showed that the cross-flow oil cooler is not sufficient to meet the cooling demand of the next 16-litres engine. Even though the two variants with the Aux-cooler easily meet the cooling demands, they are still not suitable for usage because they demand additional components which decrease the realibility and increase the cost. Furthermore the concept with the Aux-cooler connected in series would cause more unfiltrated oil in the system. The concept with the counter-flow oil cooler showed good potential to meet the construction requirements of cooling at full load and maximum power without conflicting with the oil system.
Abstract
In the heat exchanger of a power transformer, oil is cooled by the atmospheric air which flows around the radiator plate either due to buoyancy effects or using any forced means. This investigation is concentrated on the flow of air due to buoyancy effects. The scope of this thesis work is to investigate the heat transfer by buoyancy driven natural convection flow in the air side radiator ducts of a transformer. The investigation is limited to vertical ducts for smooth planar, smooth folded and rib-roughened geometries subjected to uniform heat flux. The study covers Rayleigh numbers ranging from 101 to 106 and focuses on the effect of channel geometry on the characteristic of flow and heat transfer as well as on the average and local Nusselt numbers. In this investigation, the effect of heat transfer with smooth planar geometry is studied and is compared with the other complex geometries. Certain parameters on the V-rib geometry are modified and its effect on heat transfer is also discussed.
All the models are designed with Gambit and the computations are done with Fluent.
Abstract
Hydro power plants generate 50% of the electric power in Sweden and most of the power plants are 50 years old. Refurbishing and modernization of the power plants are increasing in the present days to increase the efficiency of the older power plants. In Vattenfall there is a plan to refurbish three hydro power plants every year for the next 10 years and EON recently launched a similar plan. Sharp heel draft tubes with are common in hydro power plants constructed 50 year ago and studies have shown that efficiency improvement can be realized by minor modification of these older designs. However, to find these improvements in a cost effective procedure, two things are needed:
1. Accurate computer simulations of the draft tube flow (CFD)
2. An effective optimization algorithm for choosing and evaluating different designs.
This Master Thesis studies how different turbulence models and boundary conditions affect the predicted flow in different geometries. As for a previous study performed within a PhD-project at Luleå Technical University (LTU) only very small improvements in the draft tube efficiency could be seen, while the modification of the draft tube to get the optimal design is in the same order as for the experiments. This can be seen as a quality assurance that the two different CFD programmes used at LTU and Vattenfall Utveckling (i.e. CFX and FLUENT) gives the same result. The sensitivity analysis of the inlet conditions for draft tube shows that the optimization result is sensitive to the inlet profile. Therefore either more information on how/if the boundary conditions are changing at the inlet of the draft tube is needed or the runner has to be included in the simulations.
Abstract
The car industry of today is exposed to hard competition. For every new car model the requirements of the engine performance and cooling capacity is increased. To increase the cooling capacity the components in the cooling system needs to be improved and the performance to be evaluated. An often used method to predict the behaviour of components and complete systems during its development is to make physical tests on a concept. This process is very time consuming and costly. An alternative technique to reduce these factors is to use a computer aided simulation tool for simulations of individual components and the total systems. The advantage of this approach is that concepts can easily be evaluated and changed if necessary.
The aim of this work is to improve and analyse a virtual model for transient heat transfer calculations of an engine cooling system in the simulation software Flowmaster. A main part of the work is to implement the air cooling circuit in the simulation model and to study the effects of the air stream through the cooling package in the front of the vehicle. To be able to simulate the air flow, CFD-simulations are consulted and the produced results are used as a boundary condition in the Flowmaster model.
The analysis consists of comparisons between the Flowmaster model and results from physical tests in a wind tunnel. The simulation results in Flowmaster show a relatively good correspondence with the wind tunnel tests. Deviations are analysed and evaluated by performing sensitivity analyses of parameters of interest.
Comparison of two different adjustment principles in a space heating system consists of hot water radiators
- An analysis of the radiator thermostatic valves performance and ability to regulate
Niklas Lindvall
Abstract
Thermostatic valves in a system of domestic radiators have the possibility to reduce the energy consumption with about 30 %. To reach a comfortable and a low energy function in a system of radiators the interaction between the valve and the thermostatic body is an important parameter.
In this thesis a detailed mathematical model of a radiator and its thermostatic valve has been produced and evaluated. This model makes possible to a dynamical comparison of two different adjustment principles named as low-flow and high-flow principle.
The high-flow method is the conventional adjustment technique and it means that the flow it set to give a temperature drop of 10-20°C across the radiator, a low temperature drop means that a low entering temperature can be used. The low-flow method is an empirical evaluated adjustment method that represents a corresponding temperature drop about 50°C. A higher temperature drop precedes a lower flow. Because of this lower flow the pressure losses can be admitted to zero.
The result of this study shows that the interplay between the radiator system parameters (pressure level, valve size, valve characteristics, etc) is more important for the thermostatic regulation ability than the choice of adjustment method.
To adjust the capacity of today manufactured thermostatic valve; a secondary choking sets the maximum. Because of the high pressure drop over this choke the authority of the regulating valve decreases.
The adjustment for low-flow systems is more important since the power tends to be more flow dependent over the regulation interval. The ability to regulate increases if a higher maximum flow is allowed; than what is purposed in a conventional low-flow system. The loss with increasing the flow is that a higher maximum power leads to larger energy loss (if the valve does not adjust) when a room is given an airing or if the thermostatic head is removed.
The accuracy of the adjustment in a high-flow system is not that important for the delivering power of the radiator and it does not normally effect the regulation ability. The main purpose of the adjustment is to restrict the minimum pressure drop to produce correct flow all over the system. To get optimal conditions for the regulation valve the pressure changes has to be minimal. Minimal percentage pressure changes in a system when valves are regulating are reached when the total system pressure is high.
An important conclusion of this report is that the simulated system will tend to be too ideal. More or less unphysical effects, like dead time and play-in details, are rather complicated to describe mathematically. This study shows however that a regulation valve with thinner proportional band has a larger possibility to get an evenly applied temperature distribution over a year, like the case adjusted by the low-flow method.
Abstract
The main dam of the hydroelectric scheme in Vatnsfell, Iceland, is 30 m high, filled with rock and is equipped with a concrete slab facing. Two spillways (an overfall spillway and a bottom outlet) are adopted for flood release and share a common energy dissipating stilling basin. In this work the flow over the overfall spillway and in the stilling basin is modeled with the CFD-software FLUENT. The aspects that are evaluated and investigated include the discharge capacity of the spillway and the water pressure on it, the forces on the baffles in the stilling basin and the velocity profile for the water flow out of the basin. The results are validated by comparison with results from hydraulic model studies on the subject.
A quite good agreement is achieved for the discharge capacity of the spillway and the pressure acting on it. The same can be said about the velocity profile at the downstream end of the stilling basin. On the other hand, worse agreement for other properties of the flow implies that more work and/or computational power are needed in order to improve the grid resolution and thereby better resolve the flow.
Abstract
I detta arbete har ett kapacitetsprov på Ringhals 1 utförts. Kapacitetsprovet rörde en säkerhetskritisk kylkedja vars syfte är att bortföra värme från ett stort värmemagasin, en bassäng bestående av ungefär 25003mvatten. Värmetillförseln till bassängen sker huvudsakligen i form av ånga som kondenseras under vattenytan. Via tre system, sammanlänkade av värmeväxlare, kyls denna kondensationsbassäng med hjälp av havsvatten. Genom mätning av flöde och temperaturer på olika ställen i kylkedjan kunde dess kapacitet bestämmas. Kylkedjans kapacitet definieras enligt KA= Q/(T_kond - T_hav) (Där Q är från kondensationsbassängen bortförd effekt) Temperaturer och flöden mättes på flertalet ställen i kylkedjan och effekten kunde på så sätt följas på sin väg från kondensationsbassängen till havet. För att göra detta möjligt, samt att öka noggrannheten i mätningarna, kompletterades befintlig mätutrustning med tillfällig mätutrustning.
Kylkedjans pumpar och värmeväxlare kan kombineras i ett antal olika uppsättningar. Under detta kapacitetsprov kördes tre olika kombinationer (driftsfall). Dessa driftsfall baseras i grunden på det inre systemets två värmeväxlare. Antingen är en av värmeväxlarna i drift eller båda. I samtliga driftsfall översteg alla beräknade kapaciteter de krav som ställs på kylkedjan.
Kylkedjans kapacitet bestämdes till:
Resultaten visar att kylkedjan är i god kondition.
Abstract
Water power is today a major energy source in Sweden. A lot of the water power plants at present are outdated and in need of improvements. A refurbishment as well as the development of new water power plants is an important task, since this could lead to significant environmental as well as economical gains. As a part of the renewal process computational fluid dynamics (CFD) plays a major role, from a industrial perspective it is a very economically favorable method as well as a time saver.
Wakes are usually unwanted effects occurring in water turbine flows and hence must accurately be accounted for in the CFD simulation. The aim of this work is to increase the understanding of what factors act to destroy the wake of a hydrofoil, and what can be done to preserve the wake while performing CFD. The effects of coarse and skew grids on the wake is examined as well as a variation of numerical schemes and turbulence model.
Abstract
For waterjet systems operating in marine ships cavitation is a phenomenon that often occur. The presence of vapor in the flow affects the performance of the pump and as the cavity grows the pump efficiency drastically reduces to a level where the pump cannot operate normally. Due to this influence on the pump performance it is of main interest to be able to predict the behaviour of the cavitation process. At Rolls Royce Hydrodynamic Research Center in Kristinehamn experiments have been performed to observe the cavitating flow in such a waterjet system. With growing demand of detail information and the ability to run faster simulations, the desire of a reliable numerical tool has increased. The aim of this work is therefore to analyse and compare different numerical cavitation models and to find a model that can be used as a complement to experiments. First, four different cavitation models have been used for solving the cavitating flow around a hydrofoil. This rather simple geometry gives fast converged solutions and hence, is a fast way of testing the different models. Two of the tested cavitation models gave promising results and have therefore been used for the simulation of the flow in a pump to a waterjet. The efficiency calculated from the solution obtained with each model has been compared to experimental data and it is concluded that one of the cavitation models shows good agreement.
Keywords: cavitation, cavitation models, computational fluid dynamics, NACA 0015, waterjet, mixed flow pump
Abstract
This report deals with numerical simulations of two-phase flows in an air/water distributor. The flows are turbulent, unsteady and the liquid phase is under different shapes along the flow: jet, layer, droplets.
The objective of this study is to establish the correct physical models for CFD simulations in order to reproduce experimental data at a wide range of water and air flows.
First, a mesh sensitivity study was made and an optimal cell size was determined for a 2D axisymmetric relevant case.
The influence of different two-phase flow settings has been studied. Nine CFD simulations on a simplified 3D geometry have been performed, with a fine mesh. Two flows having different associated Weber numbers (<1 and ~30) have been considered. VOF simulations have been compared with Euler/Euler simulations. Euler/Euler simulations have been performed with two different liquid phase characteristic lengths. The differences in the results are not significant but they are clearer for the case where the Weber number is less than one, i.e. the case where the surface tension effects are stronger.
Finally, entire simulations of the flow have been performed for eight different operating conditions among the experimental data and using an Euler/Euler model. The Euler/Euler model is more adapted for the simulation of a dispersed flow. The simulated cases can be classified as follow:
Weber ~ 30
Weber ~ 10
Weber < 3
The post-treatment of simulations results consists in comparing the simulations water distribution downstream the distributor with the experimental data. This comparison shows that for Weber ~ 30 the CFD simulations are predictive.
Key words: VOF, Euler/Euler, two-phase flows, CFD, Weber number
Abstract
The objective of the present work is to study the ERCOFTAC conical diffuser, focusing on the validation of different cases with a CFD (Computational Fluid Dynamics) software called OpenFOAM. Therefore, the aim is to provide turbomachinery designers with an OpenSource software which gives results close to the reality. Since the studies are focused on the hydro turbine draft tube, the numerical simulation solves the incompressible flow throught a conical diffuser. The validation is made comparing the computational results with respect to the ERCOFTAC measurement data. The fields analysed are domain geometry, discretization scheme, pressure equation solver, turbulence model and boundary conditions. The best results are obtained with a domain geometry with a dump after the conical diffuser (called Case2) which supplies similar outlet conditions of the diffuser as in the measurements.
Keywords: Draft tube, hydro turbine, conical diffuser, CFD, OpenFOAM.
This work is a combination of Finite Element (FE) modelling and Computational Fluid Dynamics (CFD) to investigate the effect of acceleration pulses, head restraint and seating posture on facet joint loads and pressure transient magnitudes on the neck injury outcome during whiplash motion.
A parametric study is carried out with the FE human body model THUMS (Total HUman Model for Safety) for a variety of crash pulses and crash conditions that have a known relative risk of long term neck injuries in rear-end impacts. The injury criterion NIC (Neck Injury Criteria) is addressed for the studies made.
The THUMS model is used to generate the motion data of the spinal canal, which is used as an input to simulate the behaviour of the spinal canal to analyse the pressure transients in the network of blood vessels during the whiplash motion performing CFD simulations using the OpenFOAM CFD toolbox. Using the output of FE simulations, a moving mesh technique is used to achieve the motion of the mesh points in the CFD simulations.
The results give an insight into proposed injury mechanisms and injury risk assessment criteria concerning long term neck injuries. The effect of head restraint and its position with respect to the driver's head in mitigating the above injuries is discussed for different crash scenarions. Keywords: Neck Injuries, Whiplash Trauma, FEM, CFD, THUMS, NIC, Facet Joint Strains and Injury Mechanism
Numerical solutions of the rotor-stator interaction using OpenFOAM-1.5-dev was investigated in the ERCOFTAC Centrifugal Pump, a testcase from the ERCOFTAC Turbomachinery Special Interest Group. The case studied was presented by Combes at the ERCOFTAC Seminar and Workshop on Turbomachinery Flow Pre-diction VII, in Aussois, 1999. It has 7 impeller blades, 12 diffuser vanes and 6% vaneless radial gap, and operates at the nominal operating condition with a Reynolds number of 6.5*10^5 at a constant rotational speed of 2000 rpm.
2D and 3D models were generated to investigate the interaction between the flow in the impeller and that in the vaned diffuser using the finite volume method. The incompressible Reynolds-Averaged Navier-Stokes equations were solved together with the standard k-epsilon turbulence model. Both steady-state and unsteady simulations are employed for the 2D and 3D models. A Generalized Grid Interface (GGI) is implemented both in the steady-state simulations, where the GGI is used to couple meshes of rotor and stator, and in unsteady simulations, where GGI is applied between the impeller and the diffuser to facilitate a sliding approach.
Several numerical schemes are considered such as Euler, Backward and Crank-Nicholson (with several off-centering coeffcients) time discretization, and upwind and linear upwind convection discretization. Furthermore, the choice of different maximum Courant Number and the different unsteady transient solvers have been studied, and the required computational time has been compared for all the cases. The ensemble-averaged velocity components and the distribution of the ensembleaveraged static pressure coeffcient at the impeller front end are calculated and compared against the available experimental data provided by Ubaldi.
The computational results show good agreement with the experimental results, although the upwind convection discretization fails in capturing the unsteady impeller wakes in the vaned diffuser. The case with a maximum Courant Number of 4 is regarded as having the most efficient set-up, predicting the unsteadiness of the ow with a large time-step.
Keywords: CFD, OpenFOAM, Turbomachinery, GGI, ERCOFTAC Centrifugal Pump
This report presents the methodology and the results of simulations of the flow in a stratified charged two-stroke engine. The focus is put on the process and performance of the scavenging. To simulate the flow through the engine the finite volume method in three dimensions is used. The OpenFOAM-1.5-dev computational fluid dynamics software is used to perform the calculations. The performance and possibilities that OpenFOAM-1.5-dev gives for this kind of applications is evaluated.
Keywords: Two-stroke engine, OpenFOAM, Mesh operations, Topology changes, Trapping efficiency
This work presents results from OpenFOAM simulations conducted on a swirl generator designed to give similar flow conditions to those of a Francis turbine operating at partial load. Francis turbines are one of the most commonly used water turbines. In these turbines, there is however a frequent problem occuring at part load. Due to a swirling flow in the draft tube, a transient helical vortex rope builds up and creates severe pressure fluctuations in the system that increase the risk for fatique. To predict and control such flow features is therefore critical. A test rig was developed at the "Politehnica" University of Timisoara, Romania, to provide a detailed experimental database of such flow features. This test rig has four parts: leaning strout vanes, stay vanes, a rotating runner which is designed to have zero torque, and a convergent divergent draft tube.
In this work, numerical results are compared and validated against measurements realized on the swirling flow test rig at the Polytechnica University of Timisoara in Romania. The computational mesh is created with ICEM-Hexa and the parts have been meshed separately and then merged together, using General Grid Interfaces (GGI) to couple them numerically. The Finite volume method is used to solve both the unsteady and steady state Reynolds Averaged Navier Stokes equations and the standard k-epsilon model is used to close the turbulence equations. Steady-state simulations is a preliminary method, which is less time-consuming and predicts the general behavior of the flow field. It also provides good initial conditions for the unsteady simulations. For the unsteady simulations, the mesh of the rotating part of the domain is rotating and the coupling between the stationary and rotating parts is handled by a sliding GGI interface.
The simulation results shows a developing vortex rope in the draft tube which gives rise to oscillations of flow properties in the system. The size and shape of this vortex rope, as well as the frequency of the oscillations it gives rise to, is highly dependent on the rotational speed of the free runner. The results show that a rotational speed of 920 rpm on the runner, corresponds best with the measurements out of the three rotational speeds 870 rpm, 890 rpm and 920 rpm. The rotational speed of 870 rpm gives a positive moment on the runner, an rpm of 890 of almost zero moment, and a speed of 920 rpm gives a positive moment on the runner. Fourier analysis of the pressure fluctuations show that several new frequencies has been introduced compared to a previous OpenFOAM study which was only made on the draft tube. The main frequencies for a rotational speed of 920 rpm have been estimated to 3.0 Hz corresponding to an extraction/retraction of the vortex rope, 18.02 Hz which comes from the rotation of the vortex rope and 153.19 Hz which is caused by the rotor stator interaction. Furthermore, the amplitudes of the fourier spectra have shown good agreement with the previous study.
Abdominal aortic aneurysm, a disorder involving a local dilatation of the abdominal
aortic vessel, is a disease common among males in their late sixties and a
major cause of death in case of rupture. An aneurysm can be treated with major
open surgery or with minimally invasive techniques. One such treatment, called Endovascular
Aortic Repair (or EVAR), is the insertion of stent grafts redirecting the
blood
ow through a bifurcating tube consisting of a special fabric supported by a
reinforcing metallic mesh. This procedure is preferrable in the sense that it does not
require an open surgery. However, there are some problems arising from the fact that
the stent graft is not xated at its lower extremities. When subjected to a pulsating
blood
ow the bifurcating portions of stent graft may thus experience detachment
from the vessel walls (commonly referred to as stent graft migration), leading to fatal
blood leakage. The forces causing such detachments are therefore of great interest.
The development of numerical methods for Fluid-Structure Interaction (FSI)
analyses provides possibilities to study the
ow through a stent graft and the forces
it exerts on the attachment regions. This report presents the results from FSI simulations
using the two softwares LS-DYNA and OpenFOAM. The scenarios studied
in this work include a steady
ow of water and a sinusoidal
ow of water through a
bent,
exible tube resembling one of the lower extremities of a stent graft. The different
softwares utilize di¿ent numerical approaches to formulate the FSI problem.
LS-DYNA uses a Finite Element (FE) based Arbitrary Lagrangian-Eulerian (ALE)
formulation, while OpenFOAM uses the Finite Volume (FV) method. In addition to
the
ow analysis and extraction of the forces, the use of the di¿ent softwares allows
for a comparison between the two numerical approaches.
For both scenarios, the
ow characteristics in the di¿ent softwares show fair correspondence
and the extracted forces are of the same orders of magnitude. However,
some previous studies, such as the work performed by Li and Kleinstreuer [1], point
towards larger forces than those extracted in this work. These di¿enes are likely
to originate from the di¿ences in geometries, material properties and boundary
conditions. Nonetheless, the results show good promise for continuation of similar
studies in the future.
Keywords: Abdominal Aortic Aneurysm, Stent Graft, FSI, OpenFOAM, LS-DYNA
Air cooled electric generators have been studied for a long time, but there is still a lack of knowledge about the details of the air flow in such machinery. In this work, a generator ventilation model was specially designed and constructed as a 1:2 model of an existing generator model in Uppsala University. Full flow Reynolds number similarity is achieved by increasing the rotation speed of the model generator. The rotor and the stator were built with rapid-prototyping techniques that could resolve the complex geometry with high accuracy. The manufacturing process also allows the inclusion of pressure taps, making it possible to measure the wall static pressure in the most interesting region. A sector of the stator was built in plexi-glass for the PIV measurements. Six configurations were investigated: two different stators with three different rotor fan blades. The rotational speed was kept constant for all cases to maintain the same Reynolds number. The static pressure at the stator coils, stator inner and outer walls, and the total pressure at the outlet of the stator channels were measured. Pressure transducer together with scanivalve were used to measure the static pressure around the coil. A custom made rake was built to measure the total pressure at the outlet of the channel. Mass flow was estimated by integrating the total pressure data from the outlet. Two static pressure taps at the top of enclosure wall was made to estimate the flow angles. Around the coil the air flow has a large tangential component when entering the stator channels. The air flow was estimated to be swirl due to high flow angle. The static pressure at the stator inner wall increases as the air flows axially in the space between the rotor and stator. Half of the stator cooling channel was occupied by recirculation region. Estimated mass flow has approximately half the value compared to numerical calculation of 100% scale generator in Uppsala in accordance with design expectations.
CFD is a very important tool in today's design of automotive air induction systems. The simulations enable the ow in a proposed design to be evaluated without manufacturing the system. Most commercial software's used for this are expensive, and in the ever increasing competition lowering costs is a key issue for a carmaker such as Volvo Car Corporation.
This thesis evaluates the use of the open source CFD code OpenFOAM for simulating the ows in air induction systems. Two test cases are used and compared to the commercial code Fluent sold by ANSYS, Inc. The results from both codes are also compared to results from physical tests.
Results from the test cases are that although a lot of time has been spent on nding viable numerical schemes and solver settings, there is still a lot of work to be done before the OpenFOAM simulations show the same numerical stability as the Fluent simulations. Because of this and that the same boundary conditions could not be used OF shows results further from the experimental results than Fluent. During the project a problem in OpenFOAM concerning oscillating velocities in the interface to porous media was discovered. Put together there is still work to be done before OpenFOAM can be used for complete air induction system simulations.
When there is no air lter involved, OpenFOAM is very suitable to use in topology optimisation. Since it is command line based it is easy to couple with optimisation software such as modeFrontier. Also investigated in this thesis is the adjoint solver in OpenFOAM. It is a simple adjoint optimiser but to be truly usable it needs extension. Adjoint optimisation in general is very useful as a guide to designers, but the results are not suitable to use directly since it doesn't take variables such as manufacturability into account.
Keywords: CFD, OpenFOAM, Air induction system, porous media, adjoint, topology optimisation
As a consequence of the current change in the electric energy supply structure and present available electric
energy storage capabilities, hydro power plants are tending to be operated on a wide spread of off-design
conditions. The operation of turbines not running at their best operating point could lead to a physical
phenomenon called helical vortex or vortex rope. Although the helical vortex has been investigated for several
decades already, it is still far from being completely understood. Moreover, it could have undesirable impacts
on the hydraulic system of the power plant, namely, an increase of the risk of fatigue failure, the development
of resonance vibration and a decrease of the efficiency of the power plant. In order to analyze the vortex rope
and to assess its effects on the hydraulic system, it is therefore in the interest of both science and industry to
simulate the physical phenomenon of the helical vortex accurately. In response to this, the Institute of Fluid
Mechanics and Hydraulic Machinery at the University of Stuttgart, Germany, constructed a Swirl Generator to
investigate a swirling flow, which is similar to the downstream of the turbine runners. With the help of eight
non-rotating blades and a conical diffuser, this test rig is capable of generating a helical vortex.
In this work, cases for the simulation of the unsteady flow in the Stuttgart Swirl Generator with OpenFOAM
are presented. To do so, this work firstly explains the background theory of the helical vortex phenomenon
and the method of Computational Fluid Dynamics. Furthermore, the underlying test rig, geometry and mesh,
discretisation schemes, algorithm for interequation coupling, solvers for the systems of linear algebraic equations
and boundary and initial conditions are elucidated. As the flow in the Swirl Generator is characterized by a
Reynolds number in a range of approximately 1.1*10^5 to 1.8*10^5 and unsteady flow features caused by the
helical vortex, the treatment of turbulence plays a vital role for an appropriate setup of the cases. Here, common
Reynolds-Averaged Navier-Stokes (RANS) turbulence models are assumed to be limited in their capability of
dealing with unsteady flows. The method of Large Eddy Simulation (LES) on the other hand, would be capable
of addressing these drawbacks, but are still unfavorable in terms of their demands on the computational effort.
This work therefore, investigates hybrid strategies, which combine the advantages of both the RANS and LES
approach. For this, cases based on two standard high-Reynolds number RANS models: k-epsilon and k-omega SST, and
three hybrid RANS-LES models: k-omega SST SAS, Spalart-Allmaras DDES and Spalart-Allmaras IDDES are set
up. In order to assess the results of the simulations, the present work shows a general evaluation of the results
and compares experimental and simulated measurement data.
Keywords: Vortex rope, helical vortex, turbulence modeling, OpenFOAM, Stuttgart Swirl Generator, DES, SAS.
Keywords:
Keywords:
Keywords:
Keywords:
Keywords:
Keywords:
Keywords:
Keywords:
Keywords:
Simulation, Optimization and Validation Measurements of Turbofan Engine Outlet Guide Vanes (pdf)
Effektivitetsanalys och energiutvinningsmöjligheter för Vigor Wave Energy Converter (pdf)
Förbättring av Francisturbin - Genom Teoretiska, Experimentella och Numeriska Studier (pdf)
Uppställning och utforskning av fall med värmeledning,
samt fri och påtvingad konvektion. (pdf)
Ökning av verkningsgrad för experimentrigg utifrån numeriska, teoretiska och experimentella metoder (pdf)
Computational Modeling of Temperature Distribution in a Freeze Room (5p project, pdf, not public)
Temporally fluctuating prey and coexistence among unequal conspecific interferers
Oikos 101:411-415, 2003
Abstract
Coexistence among unequal conspecific interferers should be unlikely to persist if stronger interferers always experience a relative fitness increment from their higher foraging rates. In this study, we suggest that decreased relative costs to weaker interferers with increasing temporal fluctuations in prey availability may be a mechanism enhancing coexistence of unequal conspecific interferers. Previous work on fluctuation and coexistence has dealt with oscillations over a time-scale measured in generations of competitor species and their resources, while our work shows that fluctuations in prey availability facilitate coexistence of different phenotypic strategies within species and generations, and over short time-scales. With increasing amplitude of temporal fluctuation about an average prey density, cumulative intakes for differently strong interferers are affected differently. Because of the prey-dependent effect of interference, high amplitudes of fluctuation allow for relatively lower foraging-rate costs in weaker interferers, which decreases the difference in foraging success between strong and weaker interferers. This decreased difference in foraging success could thus significantly relax the conditions allowing for unequal interferer coexistence.
P. A. Nilsson and G. D. Ruxton, Div. of Environmental and Evolutionary Biology, Univ. of Glasgow, Glasgow, G 12 8QQ, U.K. Present address for PAN : Ecology Building, Lund Univ., SE- 223 62 Lund, Sweden (anders.nilsson@limnol.lu.se ). J. H. Nilsson, Thermo and Fluid Dynamics, Chalmers Univ. of Technology, Gothenburg, Sweden.
Numerisk beräkning av strömning vid ledskenor och löphjul i vattenturbiner
SMD01, 2001, Linköping
Elforskdagen, 2002, Stockholm
Abstract
Presentationen beskriver erfarenheter och slutsatser av en nyligen försvarad avhandling i numeriska beräkningar av turbulent strömning i vattenturbiner. Projektet ingick som en del av det pågående nationella vattenturbinteknikprogrammet som sponsras av ELFORSK, Energimyndigheten och GE Energy (Sweden) AB.
Avhandlingen beskriver huvudsakligen beräkningsresultat från strömningen kring löphjulen i en Kaplanturbin och en Francisturbin. Den studerade Kaplanturbinen är en modell av turbinerna i Hölleforsen. Modellen har studerats experimentellt i Vattenfall Utveckling AB:s laboratorie i Älvkarleby och den har använts som testfall i två workshops inom ramarna för vattenturbinteknikprogramet. Den studerade Francisturbinen är den s.k. GAMM-turbinen, som använts som testfall i workshops sedan 1989. Även denna turbin är i modellskala och den har studerats experimentellt i LMH-IMHEF-EPFL:s laboratorie i Lausanne. För båda turbinerna har experimentella observationer och detaljerade mätningar av strömningen gjorts. De experimentella resultaten har använts för att bekräfta de numeriska beräkningarna som utförts i avhandlingen.
Den turbulenta strömningen kring löphjul i vattenturbiner ställer stora krav på beräkningsverktyget. Exempelvis kräver de mycket tunna gränsskikten vid bladytorna att ett mycket stort antal beräkningsceller används. Normalt används s.k. vägg-funktioner i gränsskikten för att minska antalet beräkningsceller, men dessa vägg-funktioner går egentligen inte att använda i dessa sammanhang. I detta arbete beräknas istället strömningen igenom hela gränsskikten. Beräkningsverktyget har utarbetats speciellt för ändamålet. Det bygger på multiblock-principen, där beräkningsblocken beräknas parallellt på separata CPUer för att snabba upp de tunga beräkningarna. Resultaten från beräkningarna överensstämmer väl med de experimentella observationer och detaljerade mätningar som gjorts. Visualisering av beräkningsresultaten bidrar till förståelsen av strömningen i vattenturbiner.
SMD03, 2003, Göteborg
SMD05, 2005, Lund
Second OpenFOAM Workshop, Zagreb, June 7-9 2007
Second OpenFOAM Workshop, Zagreb, June 7-9 2007
Second OpenFOAM Workshop, Zagreb, June 7-9 2007
Second OpenFOAM Workshop, Zagreb, June 7-9 2007
SMD07, 2007, Luleå, ISSN 1402-1528 / ISRN LTU-FR--07/10--SE / NR 2007:10, pp. 56
Polhemslaboratoriet, Avdelningen för datorstödd maskinkonstruktion, Luleå Univ. of Technology, Luleå, Sweden
Håkan Nilsson
SMD07, 2007, Luleå, ISSN 1402-1528 / ISRN LTU-FR--07/10--SE / NR 2007:10, pp. 57
SMD07, 2007, Luleå, ISSN 1402-1528 / ISRN LTU-FR--07/10--SE / NR 2007:10, pp. 54
Third OpenFOAM Workshop, Milano, July 9-11 2008
Third OpenFOAM Workshop, Milano, July 9-11 2008
BATCHELOR THESES
Selma Bengtsson, Erik Haglund, Linda Noreheim, Johan Söder, Mats Åslund, Fredrik Önnheim
Frida Holmquist, Oliver Salamon, Linn Svärd, Kristoffer Weywadt
(Håkan Nilsson was consulted, but was not part of the project)
Eskil Nilsson, Ivar Nilsson, Oskar Thulin, Sebastian Samuelsson
Oscar Bergman
STEFAN ASK, ROBIN DOVIK, BASHAR FATAHALLA, JOHAN SPARLUND
MINOR STUDENT PROJECTS
Björn Margeirsson
Lots of CFD projects from problem based courses.
ECOLOGY PAPERS
P. Anders Nilsson, Graeme D. Ruxton and J. Håkan Nilsson
CONFERENCE PRESENTATIONS WITHOUT PUBLICATIONS
Håkan Nilsson
Chalmers Univ. of Technology, Göteborg, Sweden
Utveckling av beräkningsmetoder för flöde i vattenturbiner
Håkan Nilsson
Chalmers Univ. of Technology, Göteborg, Sweden
Beräkning av strömning i vattenturbiner
Håkan Nilsson
Chalmers Univ. of Technology, Göteborg, Sweden
Beräkning av strömning i vattenturbiner
Håkan Nilsson
Chalmers Univ. of Technology, Göteborg, Sweden
OpenFOAM Turbomachinery Working Group
Maryse Page and Håkan Nilsson
Hydro Quebec / Chalmers
OpenFOAM activities at Chalmers and within the Swedish Water Power Center
Håkan Nilsson
Chalmers
Numerical Calculations of Rotordynamical Coefficients and Forces on a Hydropower Turbine Runner Using OpenFOAM
Martin Karlsson and Håkan Nilsson
Luleå University of Technology / Chalmers
Open Subversion Repository Access For OpenFOAM
Martin Beaudoin, Bernhard Gschaider, Hrvoje Jasak and Håkan Nilsson
Hydro Quebec / ICE Strömungsforschung GmbH / Wikki Ltd. / Chalmers
CFD for water power using OpenFOAM
Håkan Nilsson
Chalmers Univ. of Technology, Göteborg, Sweden
Strömningsexciterade svängningar i vattenkraftturbiner - Hur ska strömningen genom en turbin modelleras i en rotordynamisk modell?
Martin Karlsson
Chalmers Univ. of Technology, Göteborg, Sweden
Turbulensmodellering för instationär virvlande strömning i sugrör
Walter Gyllenram
Chalmers Univ. of Technology, Göteborg, Sweden
OpenFOAM Turbomachinery Working Group: Progress report
Maryse Page and Håkan Nilsson
Hydro Quebec / Chalmers
OpenFOAM Turbomachinery Working Group: ERCOFTAC conical diffuser case-studies
Maryse Page, Håkan Nilsson, Olivier Petit, Omar Bounous
Hydro Quebec / Chalmers / Chalmers / Chalmers
Air-water interaction in bottom outlets. An ambition within SVC - the Swedish Hydropower Centre
(part 1)
(part 2)
Patrik Andreasson, Vattenfall research and develeopment,
Håkan Nilsson, Chalmers University of Technology
SIAMUF 2009
SIMDI 2009
Fourth OpenFOAM Workshop, Montreal, June 1-4 2009
Fourth OpenFOAM Workshop, Montreal, June 1-4 2009
Fourth OpenFOAM Workshop, Montreal, June 1-4 2009
3rd IAHR International Meeting of the WorkGroup on Cavitation and Dynamic Problems in Hydraulic Macinery and Systems, Brno, Czech Republic, October 14-16, 2009
Fifth OpenFOAM Workshop, Gothenburg, June 21-24 2010
| OTHER |
Öppnar dörren för bättre svetsprocesser
Special issue in NyTeknik, December 14, 2011, page 7
Generation of numerical human models based on medical imaging
Marta González Carcedo, Karin Brolin
Contributions by Håkan Nilsson