|NUMERICAL INVESTIGATIONS OF TURBULENT FLOW IN WATER TURBINES|
Publications: [1-17], see references below
Start of project : Spring 1997
A parallel multiblock finite volume CFD (Computational Fluid Dynamics) code CALC-PMB (Parallel MultiBlock) for computations of turbulent flow in complex domains has been developed and used for the computations of the flow through water turbines. The main features of the CALC-PMB CFD code are the use of conformal block structured boundary fitted coordinates, a pressure correction scheme (SIMPLEC), cartesian velocity components as the principal unknowns, and collocated grid arrangement together with Rhie and Chow interpolation. The computational blocks are solved in parallel with Dirichlet-Dirichlet coupling using PVM (Parallel Virtual Machine) or MPI (Message Passing Interface). During the computations, the computational blocks are assigned to separate PVM or MPI processes. The level of parallelization is thus determined by the block size distribution and the distribution of the processes on the available processors. The parallel efficiency is excellent, with super scalar speedup for load balanced applications. The ICEM CFD/CAE grid generator is used for grid generation and Ensight, Tecplot and Matlab are used for post-processing.
To be able to investigate the results from computational fluid dynamics in a Cave Automatic Virtual Environment (CAVE), a close collaboration with people at Chalmers Medialab and people at CERCA was established during 2000. The people at CERCA have developed a configurable visualization software tool for the display and analysis of numerical solutions. The software is called Vu. A short description of 3D visualization of water turbine flow using Vu can be found here.
Two different types of water turbines are investigated:
THE KAPLAN WATER TURBINE
This work is focused on tip clearance losses in Kaplan water turbines (figure 1), which reduces the efficiency of the turbine by about 0.5%. The investigated turbine is a test rig, at GE Energy (Sweden) AB, with a runner diameter of 0.5m (figure 2). It has four runner blades and 24 guide vanes. The tip clearance between the runner blades and the shroud is 0.25mm.
THE GAMM FRANCIS WATER TURBINE
This work investigates the turbulent flow in a Francis water turbine (figure 3). The GAMM Francis turbine (figure 4) is used for validation of the CALC-PMB CFD code in the area of hydraulic machinery. The investigated Francis runner has 13 runner blades. Detailed measurements of the flow in this turbine was performed in conjunction with the GAMM Workshop in 1989. This validation is performed in a collaboration with LMH - IMHEF - EPFL in Lausanne, Switzerland, where three months of the work was carried out.
To resolve the turbulent flow in the tip clearance and the boundary layers, a low Reynolds number turbulence model is used. Because of computational restrictions, complete turbine simulations found in the literature usually use wall functions instead of resolving the boundary layers, which makes tip clearance investigations impossible. Since part of the computational domain is rotating, Coriolis and centripetal effects are included in the momentum equations. At this stage, the k-\omega model of Wilcox, which can be integrated all the way to the wall, is used without terms for rotational effects. This is common in turbomachinery computations for reasons of numerical stability and the small impact of such terms in these kinds of industrial applications. To resolve the turbulent boundary layers and the tip clearance at the same time that the grid size should be kept as low as possible and the control volumes as orthogonal as possible, the computational grid is created in a multiblock topology using ICEM CFD/CAE. The computations of both the guide vanes and the runner are confined to a single guide vane or runner blade. This includes no extra restrictions since the boundary conditions are assumed to be stationary axisymmetric and the stationary Reynolds averaged solution is thus periodic.
Since we are developing the code ourselves, we are in full control of numerical errors, assumed approximations, etc. We can easily implement new turbulence models or exchange the numerical solver so that we can do Large Eddy Simulations (LES) using different subgrid models.
The computational results are in accordance with observations made by GE Energy (Sweden) AB and the GAMM measurements. Some results are presented below as figures with captions. Download the references presented below for a more thorough investigation and discussion of the results.
The introduction of CFD in the area of hydraulic machine research is believed to increase a detailed knowledge of the flow inside the machines and to speed up the design procedure. This requires that the experience from CFD in this area is increased, which cannot be achieved without detailed experimental investigations to be used for comparisons. With sufficient experience of CFD in the area of hydraulic machine research, CFD will definitely be used in future hydraulic machine development.
The work is carried out in cooperation with GE Energy (Sweden) AB. They have supplied the geometry of a part of a Kaplan water turbine including guide vanes and runner blades.
Part of the work is carried out in cooperation with LMH - IMHEF - EPFL in Lausanne, Switzerland, where three months of the work was carried out. They have supplied the geometry and performed the measurements of the GAMM Francis turbine.
A thesis for the degree of Doctor of Philosophy was presented on August 30, 2002.
- click to view postscript file
|1||H. Nilsson & L.Davidson: An implementation of a parallel multiblock extension to the CALC-BFC code using PVM for simulating the flow over sedimentary furrows, Diploma Thesis. Rept. 97/3, Thermo and Fluid Dynamics, Chalmers University of Technology, Gothenburg, 1997|
|2||H. Nilsson & L.Davidson: A parallel multiblock extension to the CALC-BFC code using PVM. Internal Report Nr 97/11, Thermo and Fluid Dynamics, Chalmers University of Technology, Gothenburg, 1997|
|3||H. Nilsson & L.Davidson: CALC-PVM: A Parallel SIMPLEC Multiblock Solver for Turbulent Flow in Complex Domains. Internal Report 98/12, Thermo and Fluid Dynamics, Chalmers University of Technology, Gothenburg, 1998|
|4||H.Nilsson & L.Davidson. Numerisk undersökning av turbulent strömning i Kaplanturbiner - statusrapport oktober 98. Vattenturbinteknik. Långsiktigt industrirelaterat FoU-program. Programskrift 1998. Sid.11-13.|
|5||S.Dahlström, H. Nilsson & L. Davidson: LESFOIL: 7-Month Progress Report by Chalmers, Technical report, Thermo and Fluid Dynamics, Chalmers University of Technology, Gothenburg, 1998. Confidential.|
|6||H. Nilsson: A numerical investigation of the turbulent flow in a Kaplan water turbine runner. Thesis for the degree of Licentiate of Engineering 99/5. ISSN 1101-9972.|
|7||H. Nilsson and L. Davidson: A numerical investigation of tip clearance flow in Kaplan water turbines. Proceedings of HYDROPOWER INTO THE NEXT CENTURY - III, 1999, p.327-335. ISBN 0 9522642 9 3|
|8||H. Nilsson and L. Davidson: A Numerical Comparison of Four Operating Conditions in a Kaplan Water Turbine, Focusing on Tip Clearance Flow. Published in the proceedings of the 20th IAHR Symposium, August 6-9 2000, Charlotte, North Carolina, U.S.A.|
|9||H. Nilsson, S. Dahlström and L. Davidson: Parallel Multiblock CFD Computations Applied to Industrial Cases. Published in the book Parallel Computational Fluid Dynamics 2000, edited by C.B. Jenssen et al.|
|10||H.Nilsson & L.Davidson. Numerical investigation of turbulent flow in Kaplan water turbines - Status report October 2000. Hydraulic Turbine Research Programme, Industrial Collaborative R&D Programme, Programme description 2000. Pages 14-17.|
|11||H. Nilsson and L. Davidson: A validation of parallel multiblock CFD against the GAMM Francis water turbine runner at best efficiency and off-design operating conditions. Internal Report 01/02, Thermo and Fluid Dynamics, Chalmers University of Technology, Gothenburg, 2001|
|12||H. Nilsson, U. Andersson and S. Videhult: An experimental investigation of the flow in the spiral casing and distributor of the Hölleforsen Kaplan turbine model. Internal Report 01/05, Thermo and Fluid Dynamics, Chalmers University of Technology, Gothenburg, 2001|
|13||H. Nilsson and L. Davidson: A numerical investigation of the flow in the wicket gate and runner of the Hölleforsen (Turbine 99) Kaplan turbine model. Proceedings of Turbine 99 II, 2001 ( Link 1 / Link 2 )|
|14||H. Nilsson and L. Davidson: Validations of CFD against detailed velocity and pressure measurements in water turbine runner flow, Int. J. Numer. Meth. Fluids 2003; 41:863-879 Not available for downloading!|
|15||H. Nilsson and L. Davidson: Application of an Angular Momentum Balance Method for Investigating Numerical Accuracy in Swirling Flow, J. Fluids Eng. 2003; Volume 125, Issue 4, pp.723-730. Not available for downloading!|
|16||H. Nilsson and L. Davidson: Detailed investigations and validations of the computed flow in the GAMM Francis runner and the Hölleforsen Kaplan runner at best and off design operating conditions. In Proceedings of the 21st IAHR Symposium.|
|17||H. Nilsson: Numerical Investigations of Turbulent Flow in Water Turbines. Thesis for the degree of Doctor of Philosophy, 2002. ISBN 91-7291-187-5.||
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