Analysis of an RNG based turbulence model for separated flows

Abstract A two-equation turbulence model of the K − e type was recently derived by Yakhot and Orszag based on Renormalization Group (RNG) methods. It was later reported that this RNG based model yields substantially better predictions than the standard K − e model for turbulent flow over a backward facing step—a standard test case used to benchmark the performance of turbulence models in separated flows. The apparent improvements obtained from the RNG K − e model were attributed to the better treatment of near wall turbulence effects. In contrast to these earlier claims, it is shown in this paper that the original version of the RNG K − e model substantially underpredicts the reattachment point in the backstep problem—a deficiency that is traced to the modeling of the production of dissipation term. However, with the most recent improvements in the RNG K − e model proposed by Yakhot and co-workers, excellent results for the backstep problem are now obtained. Interestingly enough, these results are not that sensitive to the details of the near wall treatment.