Faculty of Engineering and Natural Sciences
Large Eddy Simulation of High Reynolds Number Flows
Livermore National Lab.
This talk presents recent progress on Large Eddy Simulations (LES) of High Reynolds Number (Re) Flows. LES is superior over Reynolds-averaged Navier Stokes (RANS) approach, as LES directly captures the dynamically important eddies in the flow. Accurate prediction of turbulent mixing is essential for successful prediction of a wide range of engineering processes, including combustion and junction flows. However, the numerical simulation of high-Re flows is hampered by computational cost, if LES that resolve the near-wall layer is employed. The cost of calculation scales like the Reynolds number to the power 2.4, making the resolution of the wall layer at high Reynolds number infeasible even with the most advanced computers. In LES, an attractive alternative to compute high-Re flows is the use of wall-layer models. Two classes of approaches are discussed in this talk: simulating the near-wall region in a global, Reynolds-averaged sense (Detached Eddy Simulation, DES) and bypassing this region altogether using wall functions.
We start introducing recently developed (discretely) energy-conserving LES solver that can handle hybrid elements. The code is used to simulate flow around a bottom-mounted circular cylinder under low Reynolds numbers. Formation of horseshoe vortices, eddies shed in detached shear layers and their interaction are discussed. Next, a hybrid RANS/LES method (DES) is introduced. In DES, substantial part of the boundary layer is modeled using RANS and the remaining regions are solved using LES. DES is first used to validate LES results of flow around a circular cylinder at a low Reynolds number and then to investigate same flow under a higher Reynolds number. Finally, an implementation of two new dynamic subgrid-scale (Lagrangian scale-dependent and mixed scale-similar) models into an existing LES code is discussed. This LES code (with dynamic models) is used to simulate atmospheric boundary layer flows for wind-energy applications. The success of the code in predicting fine-scale turbulent structures is presented.
We will conclude by identifying some potential applications of these codes (in mechanical, biomedical engineering and renewable energy systems) and discuss some ideas that will further extend the range of applications that can be handled by them.
January 7, 2010, 14:40,