Large-eddy simulation of the Boeing speed bump with slip-wall boundary conditions*

Traditional wall models for large-eddy simulation (LES) rely on Reynolds-averaged Navier-Stokes (RANS) closure models to provide wall-stress boundary conditions to the LES equations. The slip wall boundary condition is derived explicitly from the LES constitutive equations and does not assume an attached boundary layer profile as is common in equilibrium boundary layer approximations (Bose & Moin, Phys. Fluids, 2014). This enables slip wall models to provide enhanced predictive capability in complex and separated flows where the thin boundary layer equations become invalid.

In this study, the high Reynolds number flow over a Gaussian bump (Boeing speed bump), with favorable and adverse pressure gradients, and turbulent separation and reattachment, is computed with a wall-modeled LES. Grid convergence of the solutions is achieved with the slip wall model for a spanwise-periodic domain section at Re=2M and simulations of a finite-span domain at Re=3.4M (aspect ratio ~ 1.0) are in agreement with recent experimental skin friction data (Gray et al., 2022). Results of the slip wall model predict a robust separation across grids while those of the equilibrium wall model with standard subgrid-scale models show a spuriously diminished separation on intermediate grid resolutions.