Micro vortex generators for boundary layer control: Principles and applications

A review is given to the major developments in the boundary layer control by means of micro vortex generator (MVG). The appearance of MVG dates back to about three decades from the present review and this class of device rapidly spreads as an efficient and robust boundary layer control strategy for flows with separation in particular. Substantial successful applications of MVG have been achieved in subsonic flows and its application into supersonic flow is under progressive development, which requires the current status and capability of MVG to be reviewed. The fundamental aspects of MVG are first summarized, including its working principle and various geometries. Understanding of the fluid mechanics involved in the wake of a MVG device is of uppermost importance: the time- averaged and instantaneous wakes are discussed respectively. In the former, effects from the MVG geometry parameters are presented; while in the latter, focus is placed on the phenomenon associated with flow instability inside the wake. MVG's applications in the subsonic regime are discussed, which covers the fundamental flow separation investigations and studies to tackle several practical problems. The ongoing studies in supersonic regime dealing with shock wave boundary layer interaction (SWBLI) induced separation are reviewed later, where the presentation is organized according to different types of SWBLI with emphasis on the interaction region.