flow around a short cylinder

Detached Eddy Simulation for Industrial Aerodynamics



Assist. prof.: Sinisa Krajnovic
sinisa@chalmers.se
Project leader: Lars Davidson
lada@chalmers.se
Cooperation: All DESider partners
Sponsors: EU project
Publications: [1-10]
Start of project: January 2004
End of project: July 2007


PROJECT
Chalmers is workng on development of hybrid LES-RANS. A one-equation RANS model is used in the near-wall region and a LES model is used in the remaining part of the flow. The matching takes place in the inner region of the log-law region.

As in imbedded LES, the interface condition between the URANS region and the LES region is crucial for the sucess of method. The resolved turbulence supplied by the URANS region to the LES region does not have any reasonable turbulent characteristics: the resolved turbulent time and length scales of the unsteady RANS flow are not representative of the real turbulence at all. A remedy is to at the interface superimpose fluctuations at the LES side of the interface. The turbulent fluctuations can be taken from a DNS of a generic boundary layer, from synthetic turbulence (the turbulence is generated in wavenumber space) or from a vortex model.

As an alternative, a hybrid model based on the k-omega model has been developed. K and omega are solved everywhere, but in the LES region the modelled length scale is taken from the filter width. The locations of matching points between the LES and the URANS region are defined from physical quantities allowing the matching points to be defined locally in space and time. This makes the method attractive for complex geometries.

Chalmers is working on four test cases: channel flow, the Ahmed body, the 3D hill and a short cylinder mounted on a wall.
 

 

 
REFERENCES
  1. L. Davidson and S. Dahlström
    "Hybrid LES-RANS: Computation of the Flow Around a Three-Dimensional Hill", Engineering Turbulence Modelling and Measurements - ETMM6, Sardinia, Italy, May 23-25, 2005.
    View PDF file
     
  2. L. Davidson
    "Hybrid LES-RANS: Inlet Boundary Conditions", 3rd National Conference on Computational Mechanics -- MekIT'05, pp. 7-22, invited paper, Eds. B. Skallerud and H.I. Andersson, 11-12 May, Trondheim, Norway, 2005.
    View PDF file
     
  3. S. Krajnovic
    "Large-Eddy Simulation of Complex Flows", EUROMECH Colloquium 469, Dresden, Germany, 6-8 October 2005.
    View PDF file
     
  4. L. Davidson and M. Billson
    "Hybrid LES/RANS Using Synthesized Turbulence for Forcing at the Interface", International Journal of Heat and Fluid Flow (to appear), 2006.

  5. L. Davidson and S. Dahlstrom
    "Hybrid LES-RANS: An Approach to make LES Applicable at High Reynolds Number", International Journal of Computational Fluid Dynamics, Vol. 19, No. 6, pp 415-427 2005.

  6. L. Davidson
    "HYBRID LES-RANS: Inlet Boundary Conditions for Flows With Recirculation", "Advances in Hybrid RANS-LES Modelling, "Notes on Numerical Fluid Mechanics and Multidisciplinary Design", Vol. 97, pp. 55-66, 2008.
     
  7. S. Krajnovic
    "Flow Around a Surface-Mounted Cylinder: A Challenging case for LES", "Advances in Hybrid RANS-LES Modelling, "Notes on Numerical Fluid Mechanics and Multidisciplinary Design", Vol. 97, pp. 305-315, 2008.
     
  8. L. Davidson
    Inlet Boundary Conditions for Embedded LES, First CEAS European Air and Space Conference, 10-13 September, Berlin, Germany, 2007.
    View PDF file
     
  9. L. Davidson
    "Using Isotropic Synthetic Fluctuations as Inlet Boundary Conditions for Unsteady Simulations" Advances and Applications in Fluid Mechanics, Vol. 1(1), pp. 1-35, 2007.
     
  10. L. Davidson
    HYBRID LES-RANS: Inlet Boundary Conditions for Flows Including Recirculation, 5th International Symposium on Turbulence and Shear Flow Phenomena, Vol. 2, pp. 689-694, 27-29 August, Munich, Germany, 2007.
    View PDF file
     


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