A Separation Control of the Diffuser Flow by the Vortex Generator Jets

In order to establish the active control system by using the vortex generator jets (VGJs), it is necessary to understand the detailed suppression mechanism of the separated flow in the diffuser. An opening angle of the diffuser can be changed from 8 to 15 deg corresponding to three flow regimes, “Unstalled”, “Appreciable Stall” and “Transitory Stall”. A micro wall flow sensor was used for measurement of forward flow fraction. It is found that VGJ makes the local forward flow fraction increase and prevents the flow detachment. Although the effect of separation control is obtained resulting from the higher jet velocity ratio, excessive jet velocity ratio introduces lower diffuser effectiveness due to the mixing loss.