Modeling the wall-slip in large eddy simulations with immersed boundaries

Abstract

We present a framework for Large Eddy Simulations (LES) with Immersed Boundaries (IBs) to simulate high Reynolds number flows over complex walls. In this approach, which we call Immersed Boundary-Modeled LES (IBMLES), we volume-filter the Navier-Stokes equations to derive the IB bodyforce. This also gives rise to the subfilter-scale (SFS) stress and residual viscous stress tensors, the latter of which is closed, and we expect the SFS stress can be closed with existing models. We show that the IB bodyforce can be closed by modeling the wall-slip velocity and provide two such models. The first is an algebraic model based on volume-filtering the Van-Driest velocity profile, and the second is a slip-length model. We perform an \textit{a priori} analysis by volume-filtering direct numerical simulation (DNS) data of turbulent channel flow at $\mathrm{Re}_{\tau}=5200$ to inform these models and investigate the behavior of the other terms in this formulation. We find streamwise wall-slip velocity is significant and both models show good agreement with volume-filtered DNS data on average. Slip velocity is non-uniform and retains a signature of inner or large scale flow structures depending on filter size. SFS terms are analogous to those in traditional LES and can likely be modeled with existing SFS models such Dynamic-Smagorinsky. Residual viscous stress is significant, so it must be considered in IBMLES. We perform filtering with multiple filter types and find there is little sensitivity to the choice of filter kernel so long as it abides by the assumptions given in this framework. Based on these results, we propose a dynamic procedure for determining slip-length that will be assessed in future studies.