Computation of Internal Separated Flows Using a Zonal Detached Eddy Simulation Approach

Abstract

This paper investigates the use of the Spalart-Allmaras one-equation turbulence model with detached eddy simulation (DES) modifications for predicting internal separated flows. For these flows, it is shown that the use of grid spacing to segregate Reynolds-averaged Navier Stokes (RANS) and large eddy simulation (LES) modes in the DES approach is cumbersome, and not practical in some cases. To allow DES to be more readily applied to such flows, a zonal approach is proposed. In this approach the LES mode in DES is only used in detached shear layer regions. These regions are dynamic, and are defined by local flow and turbulence quantities during the computation. No blending of RANS-based and LES-based regions is used in the approach such that the attached shear layer calibration of the underlying RANS-based turbulence model is not affected. The zonal DES approach is applied to two internal flows: a stenosis in a pipe and a 180° turn-around duct. Results show that the zonal DES predictions are in excellent agreement with the experimentally measured velocity profiles and pressure distributions, and are significantly improved relative to RANS predictions.