Wall-layer modeling for high-Reynolds number prediction using Large Eddy Simulation
Kyle D. SquiresMechanical and Aerospace Engineering Department.
Arizona State University, USA.
Wednesday, April 21, 10:30 CERFACS Conference Room
Abstract
The principal challenge in the Large Eddy Simulation (LES) of wall-bounded flows is the rate at which the computing cost increases with Reynolds number. If the buffer layer and its streaks are resolved, the subgridscale stresses are not substantially larger than the viscous stresses and the cost-scaling of the technique is the same as that for Direct Numerical Simulation. This in turn provides strong motivation for `wall modeling' in which the near-wall streaks and some of the eddies in the logarithmic layer are not resolved. This seminar will present approaches to wall-layer modeling for LES of high Reynolds number boundary layers. A particular focus will be on application of Detached-Eddy Simulation (DES), which combines a Reynolds-averaged Navier-Stokes (RANS) prediction of the modeled region ('RANS region') with Large-Eddy Simulation of the outer flow ('LES region'). The technique is applied to prediction of fully-developed turbulent channel over a wide range of Reynolds numbers, from 180 to 80,000 based on the friction velocity and channel halfwidth. The simulations show that DES applied without any adjustment to the underlying turbulence model yields logarithmic velocity profiles in the RANS and LES regions, but with an adjustment between the two layers in the vicinity of the interface between the two regions. The lack of structural content in the near-wall layer leads to an inaccurate interaction between the modeled and resolved layers, resulting in under-predictions in the skin friction of O(15) percent. Inclusion of stochastic forcing, accounting for backscatter of energy from the subgrid to the resolved motions, is demonstrated to eliminate the error in the skin friction prediction. The response of the method to variations in the grid resolution and Reynolds number will be discussed, in addition to recent extensions to turbulent heat transfer.
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