Control of separation in a conical diffuser by vortex generator jets

Abstract

To develop a vortex-generator-jet (VGJ) method for separation control an experimental study was carried out using a 14 deg conical diffuser with and without VGJs. Static pressure recovery coefficient and a coefficient for loss of total pressure were both used as criteria to evaluate the effectiveness of several VGJ arrangements where two geometric parameters, jet-hole-size and the number-of-jets, were varied. It was found that VR (ratio of jet speed to freestream velocity) rather than Qj/Qm (ratio of jet flow-rate to total flow-rate) is more useful as a key parameter to understanding the control of the separation in a diffuser because the effects of change of geometrical parameters tend to be reduced. The total pressure losses were reduced by increasing VR up to values near 1.5 to 2.0 where losses reached a minimum. Due to the increasing losses associated with the production of the jets, total pressure losses increase with further increase of VR beyond 2.0.