Wall-Modeled LES: Recent Experience in Nonequilibrium Flows and Thoughts on Its Convergence

Abstract Professor Park will summarize the research on wall-modelled LES (WMLES) conducted in his group, with the primary goal of assessing state-of-the-art wall models in controlled nonequilibrium flows and producing a better understanding of the notion of convergence in inherently under-resolved wall-modelled LES calculations. He will discuss application of three wall models to a spatially developing three-dimensional boundary layer in a bent square duct, where an analysis of flow angle reveals that it has separable contributions from the equilibrium and nonequilibrium parts. The latter is shown to control the accuracy of the near-wall flow direction in wall models. Two streamwise pressure gradient flows, one with flow separation and one without, will be covered. While the wall models accounting for more of the near-wall physics tend to perform better in the adverse pressure gradient (APG) region as demonstrated in many earlier studies, the most comprehensive two-layer model shows suboptimal performance in the favorable pressure gradient region (FPG) with overshoot in the skin friction, which has been discussed rarely. The mean and turbulence quantities away from the wall are predicted equally well with different wall models. Numerical experiments that indicate the convergence rate of WMLES is controlled by the extent of the wall-modeled region will be presented, suggesting that one may converge WMLES at the desired grid resolution.

Bio:  George Park is an Assistant Professor of Mechanical Engineering and Applied Mechanics at the University of Pennsylvania. He received his Ph.D. and M.S. in Mechanical Engineering (ME) from Stanford University in 2014 and 2011, respectively, and his B.S. in ME from Seoul National University, South Korea in 2009. He worked as a postdoctoral fellow and an engineering research associate at the Center for Turbulence Research (Stanford) prior to joining UPenn as a faculty member. His research interests include high-fidelity numerical simulation of complex wall-bounded turbulent flows, computational methods with unstructured grids, non-equilibrium turbulent boundary layers, and fluid-structure interaction.