TURBULENT-FLOW PAST A BACKWARD-FACING STEP - A CRITICAL-EVALUATION OF 2-EQUATION MODELS

The ability of two-equation turbulence models to accurately predict separated flows is analyzed from a combined theoretical and computational standpoint. Turbulent flow past a backward-facing step is chosen as a test case in an effort to resolve the various conflicting results that have been published during the past decade concerning the performance of two-equation models. The results obtained demonstrate that errors in the reported predictions of the K-epsilon model have two major origins: 1) numerical problems arising from inadequate resolution, and 2) inaccurate predictions for normal Reynolds stress differences arising from the use of an isotropic eddy viscosity. Inadequacies in near-wall modeling play a substantially smaller role. Detailed calculations are presented that strongly indicate that the standard K-epsilon model-when modified with an independently calibrated anisotropic eddy viscosity-can yield surprisingly good predictions for the back-step problem.