Evaluation of the unsteady RANS capabilities for separated flows control

Nowadays, unsteady RANS methods are the only techniques usable in the industry to design a control device based on a periodic excitation of the flow. This paper aims at evaluating the potential of such methods by comparing their performances with respect to LES computations taken as a reference. The chosen test case is a rounded backward facing step proposed by Dandois et al. [1]. The frequency response of this flow to the periodic excitation of a synthetic jet is computed both with LES and with four different URANS models. It is demonstrated that the optimal frequency identified by best URANS models is close to the one of LES. Nevertheless, the amplitude of separated bubble surface reduction is underestimated by URANS models.

► The separation control by synthetic jet was investigated both with URANS and LES.
► URANS is capable of finding the optimal forcing frequency.
► Nevertheless, URANS does not provide quantitative estimation of the separation bubble extent.