Detached-Eddy Simulations of Attached and Detached Boundary Layers

Abstract

This article presents Detached-Eddy Simulations (DESs) of attached and detached turbulent boundary layers. This hybrid Reynolds Averaged Navier-Stokes (RANS) / Large Eddy Simulation (LES) model goes continuously from RANS to LES according to the mesh definition. We propose a parametric study of the model over two “academic” configurations, in order to get information on the influence of the mesh to correctly treat complex flow with attached and detached boundary layers. The first case is the simulation of a compressible temporally evolving turbulent boundary layer (TBL). We check here the DES behavior for an “over-resolved” attached TBL, in order to understand how the upstream-attached flow before separation would be modeled in a more complex configuration. Effects of change of the Cdes constant are scrutinized, and the use of an additional constant is assessed. The second case is the simulation of an established laminar compressible boundary layer suddenly exposed to an adverse pressure gradient. The mean flow deceleration is imposed by means of a suction at the upper side of the computational domain, leading to separation and transition to turbulence. The effect of increasing grid size (Dz) in the spanwise direction (leading to an extension of the region treated by the RANS model and s to an increase of eddy-viscosity) is scrutinized. Conclusions are then drawn from these two test cases for DES meshing strategy that should be used in more complex configurations.