Embedded LES-to-RANS boundary in zonal simulations

Abstract

The RANS inflow boundary of a zonal LES/RANS simulation requires distributions of the averaged flow values and the turbulent viscosity. The mean flow data can be directly obtained by averaging the unsteady LES data, whereas the turbulent viscosity has to be reconstructed. Three methods to determine the turbulent viscosity are presented and tested using turbulent channel flow. The best method, i.e. the approach providing the smoothest transition from the LES to the RANS regime, being based on the turbulent kinetic energy k and the turbulent frequency ω, whereas the determination of ω is based only on derivatives of mean velocities, is used to compute a fully coupled LES/RANS channel flow to evidence the overall performance of the formulation. Finally, a zonal LES/RANS computation of a flat plate flow is performed, and the results are compared with a pure RANS simulation. The findings of the internal and the external flow problems show the formulation of the embedded boundary to be stable and to yield convincing distributions in the LES-RANS transition region.

Keywords:

• Zonal RANS/LES
• RANS inflow