LES and VLES for Shock/Boundary Layer Interaction
PhD student: Christian Wollblad
wollblad@chalmers.se
Supervisor: Lars Davidson
lada@chalmers.se
Co-supervisor: Lars-Erik Eriksson
lee@chalmers.se
Cooperation: Dept. of Mechanics, KTH and Dept. of Energy Technology, KTH
Sponsors: STEM
Publications: [1]
Start of project: November 2001
End of project: December 2006


THE PROJECT
Due to the relatively large computational cost of CFD analysis based on LES, especially for cases with small scale energetic structures such as boundary layers and free shear layers, there is currently a substantial amount of on-going research concerning alternative methods which combine the merits of RANS and LES while at the same time avoiding their drawbacks. The basic idea is to use a considerably coarser filtering of the flow equations, retaining only the very largest instationary structures, and to use a sub-grid scale model which blends smoothly between a standard RANS type model and a standard LES type model. The objective is to obtain an instationary RANS treatment of small-scale structures such as boundary layers and shear layers, the usual SGS treatment of intermediate scales and finally exact treatment of the very largest scales. This approach may be motivated by scale separation, i.e. since the smallest scales are significantly smaller than the filter length scale the filtering may be approximated by an ordinary averaging operator, yielding the well known RANS equations in instationary form. Common names for this type of modelling are very large eddy simulation (VLES), coherent scale capturing (CSC) or hybrid RANS-LES modelling.

In the first phase of this project we are doing LES simulations of the flow in a 2D bump, but at a lower Reynolds number. Periodic boundary conditions are employed in the spanwise direction. Instantaneous DNS data from fully developed channel flow are used as inlet boundary conditions. An explicit, compressible Runge-Kutta code is used. Since the solver is explicit, we are faced with severe restrictions on the time step, since the largest CFL number is based on the speed of sound and the smallest cell side. This occurs near the wall in the wall-normal direrection. To get around this restriction, a 1D implicit solver has been developed which is used in the wall-normal dirction near the wall.

The overall goals of this task are two-fold:
  • To advance our knowledge and understanding of compressibility-turbulence interactions in shock-boundary layer interaction;
  • To extend our experience, competence and tools in the area of LES and VLES techniques for compressible flows (advanced turbulence modelling, numerics, etc)

 

 
REFERENCES
  1. C. Wollblad, L.-E. Eriksson and L. Davidson
    "Semi-implicit Preconditioning for Wall-bounded Flow", 34th AIAA Fluid Dynamics Conference and Exhibit, AIAA paper 2004-2135, Portland, Oregon, 2004
    View PDF file
     
  2. C. Wollblad, L. Davidson and L.-E. Eriksson
    "LES of Transonic Flow with Shoch/Turbulent Boundary Layer Interaction" AIAA Journal, Vol. 44(10), pp. 2340-2353, 2006.
     
  3. C. Wollblad
    "Large Eddy Simulation of Transonic Flow with Shock Wave/Turbulent Boundary Layer Interaction", thesis of Lic. of Engng, Dept. of Thermo and Fluid Dynamics, Chalmers University of Technology, Göteborg, 2004.
    View PDF file
     
  4. C. Wollblad and L. Davidson
    "POD based reconstruction of subgrid stresses for wall bounded flows using neural networks", 5th International Symposium on Turbulence, Heat and Mass Transfer", Dubrovnik, Croatia, September 25-29, 2006.
    View PDF file
     
  5. C. Wollblad and L. Davidson
    "POD based reconstruction of subgrid stresses for wall bounded flows using neural networks (selected paper)", Flow, Turbulence and Combustion, Vol. 81, No. 1-2, pp. 77-96, 2008.
     
  6. C. Wollblad, L. Davidson, L.-E. Eriksson
    Investigation of large scale shock movement in transonic flow, Int. J Heat Fluid Flow, Vol. 31(4), pp. 528-535, 2010 available here


This page, LES and VLES for Shock/Boundary Layer Interaction, should be part of a frames system at www.tfd.chalmers.se/~lada/projects/proind.html
 
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