Critical Evaluation of K-.EPSILON. and K-T Turbulence Models in Two-Dimensional Flow over a Backward-Facing Step.

Abstract

The capability of two-equation K-e and K- T models to predict separated flows is investigated from the computational standpoint. The flow over a backward-facing step is chosen as a test problem. A method of lines approach is adopted as a numerical method. The spatial derivatives are discretized by the second order central and upwind difference approximations. As a time integration scheme a rational Runge-Kutta method is used. In the first place, a variety of low-Raynolds number K-e and K-T (Launder-Sharma, Lam-Bremhorst, Speziale) models are tested. It is found that the Launder-Sharma model predicts the reattachment length more closely to the experimentally measured value than the other two models, and that the dumping function used in the Lam-Bremhorst or Speziale model is not appropriate for separated flows. In the next place, it is found that the use of the anisotropic eddy-viscosity models predicts normal stress better than the isotropic model, whereas the computed reattachment length and mean-velocity profile are not greatly improved by the use of the anisotropic models.