Flow separation control and performance evaluation of an asymmetric diffuser using vortex generators

Abstract

Results are presented from a RANS study of an asymmetric diffuser with mild separation incorporating a vortex generator (VG) at the entrance. Three types of VGs in the form of a pyramidal ramp, and a pair of vanes that produces an upwash or a downwash respectively in the channel between them. In total, twelve VG configurations were included in this study. The flowfield downstream of the VG was analyzed using limiting streamlines. It was found that the VGs disrupted the two-dimensionality of the undisturbed flow, generally reducing the separation zone. In some cases, the separation bubble was split into two. The preliminary examination of the flow structures downstream of the VGs will help to improve the understanding of the underlying flow physics of VGs. The overall drag of the diffuser was analyzed using a non-dimensional parameter ΔCD obtained from a control volume analysis. None of the VGs caused the overall drag of the diffuser to decrease, with the best performance being no decrease. In the best case involving vanes that produce a downwash, an improvement was obtained in the distortion index. This study shows that there is promise in improving diffuser flows through placing vanes at the entrance.