Visualization of pulsed vortex generator jets for active control of boundary layer separation

TLDR: In this paper, the interaction of pulsed vortex generator jets with a zero pressure gradient turbulent boundary layer has been studied from the perspective of vorticity dynamics, and the improved performance of the generator jets is attributed to the formation, stretching and bending of the starting vortex ring in these jet flows.

Abstract: The interaction of pulsed vortex generator jets with a zero pressure gradient turbulent boundary layer has been studied from the perspective of vorticity dynamics. The improved performance of the pulsed vortex generator jets is attributed to the formation, stretching and bending of the starting vortex ring in these jet flows. The shear in the boundary layer amplifies the vorticity of the starting ring and re-directs it into the streamwise direction. The pitching and skewing of the jet is necessary to create the initial tilt of the starting vortex ring with respect to the mean flow. The source of the supplementary streamwise vorticity is the jet boundary layer fluid, which rolls up into the starting vortex in the initial phase of jet ejection. Flow visualization experiments confirmed that the extra benefits obtained from pulsing the vortex generator jets stems from the alteration of flow structure. The pulsed VGJs create vortex ring-like structures that are inclined with respect to the freestream.