This paper represents the results of an experimental program with the aim of controlling the flow in a highly unstable 90deg curved diffuser. The diffuser, which is an integral part of an open jet wind tunnel at the University of Southampton, has the unique configuration of extreme shortness and high area ratio. In this study, several passive flow control devices such as vortex generators, woven wire mesh screens, honeycomb, and guide vanes were employed to control the three-dimensional diffusing flow in a scaled-down model. Although less successful for vortex generators, the other devices were found to improve significantly the uniformity of the flow distribution inside the curved diffuser and hence the exit flow. This study suggests that a cumulative pressure drop coefficient of at least 4.5 at the diffuser exit with at least three guide vanes is required to achieve adequate flow uniformity at the diffuser exit. These flow conditioning treatments were applied to the full-scale diffuser with exit dimensions of 1.3×1.3m2. Flow with comparable uniformity to the scale-model diffuser is obtained. This study provides valuable guidelines on the design of curved/straight diffusers with nonseparated flow and minimal pressure distortion at the exit.
Passive flow control of shock-induced dynamic stall via surface-based trapped vortex generators
