A PERFORMANCE COMPARISON OF THE STANDARD K-EPSILON MODEL AND A DIFFERENTIAL REYNOLDS STRESS MODEL FOR A BACKWARD-FACING STEP

A differential Reynolds stress model (RSM) based on Launder, Reece, an d Rodi (LRR) is formulated with appropriate wall functions and applied to predict Be backward-facing step problem of Driver and Seegmiller. Numerical prediction obtained with the LRR, with and without ''wall re flection'' terms in the pressure strain model, are compared with the r esults of standard k-epsilon model of Launder and Spalding for the ste p problem. The results demonstrate that both LRR models, i.e., with an d without wall reflection terms, are capable of capturing the secondar y bubble near the step, as observed in the experiment, whereas the sta ndard k-epsilon model fails to predict the secondary bubble. In additi on, the mean velocity profiles obtained with the LRR models agree bett er with the experimental data than those by the k-epsilon model, parti cularly inside the recirculating flow region. It also emerges from the present study that, with proper wall functions, LRR model is capable of predicting recirculating flows at least as well as the original LRR model does without the ''wall reflection'' terms.