Large-Eddy Simulation/ Reynolds-Averaged Navier-Stokes Hybrid Schemes for High Speed Flows

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Title: Large-Eddy Simulation/ Reynolds-Averaged Navier-Stokes Hybrid Schemes for High Speed Flows
Author: Xiao, Xudong
Advisors: F. R. DeJarnette, Committee Member
J. R. Edwards, Committee Member
R. E. Funderlic, Committee Member
D. S. McRae, Committee Member
H. A. Hassan, Committee Chair
Abstract: Three LES/RANS hybrid schemes have been proposed for the prediction of high speed separated flows. Each method couples the k—ζ(Enstrophy) RANS model with an LES subgrid scale one-equation model by using a blending function that is coordinate system independent. Two of these functions are based on turbulence dissipation length scale and grid size, while the third one has no explicit dependence on the grid. To implement the LES/RANS hybrid schemes, a new rescaling-reintroducing method is used to generate time-dependent turbulent inflow conditions. The hybrid schemes have been tested on a Mach 2.88 flow over 25 degree compression-expansion ramp and a Mach 2.79 flow over 20 degree compression ramp. A special computation procedure has been designed to prevent the separation zone from expanding upstream to the recycle-plane. The code is parallelized using Message Passing Interface (MPI) and is optimized for running on IBM-SP3 parallel machine. The scheme was validated first for a flat plate. It was shown that the blending function has to be monotonic to prevent the RANS region from appearing in the LES region. In the 25 deg ramp case, the hybrid schemes provided better agreement with experiment in the recovery region. Grid refinement studies demonstrated the importance of using a grid independent blend function and further improvement with experiment in the recovery region. In the 20 deg ramp case, with a relatively finer grid, the hybrid scheme characterized by grid independent blending function well predicted the flow field in both the separation region and the recovery region. Therefore, with 'appropriately' fine grid, current hybrid schemes are promising for the simulation of shock wave/boundary layer interaction problems.
Date: 2003-02-05
Degree: PhD
Discipline: Aerospace Engineering

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