Effect of Rotating Cylinder at Variable Location to Control Base Flows at Mach 2

Experimental investigation of supersonic base flow has been carried out to see the effect of the cylinder when rotated counter-clockwise inside the dead zone at variable locations near its base to control base pressure for different levels of expansion for area ratio 9. The cylinder of 2 mm diameter rotating counter-clockwise, when seen from the top, is mounted as a controller. Three locations are chosen from the sidewall of the square duct namely at 2, 4, 6 mm respectively, and one from the square nozzle exit at 8 mm in the base region to mount the controller. Base pressure in the recirculation zone and wall pressure along the square duct length has been measured with and without control. The experiments were carried out at Mach 2 for NPR 2, 3, 6, 7.8, and 8.5. Cylinder when rotated counter-clockwise as an active controller was found to reduce the base drag as high as 62 percent at NPR 8.5 when located near the duct wall and 50 percent when located away from the duct wall for the same NPR. For perfectly expanded flows at NPR 7.8 the reduction in base drag was approximately from 44 to 53 percent near the duct wall depending on the location of the controller. The active controller was up to 19 percent effective for over-expanded flows near the duct wall and up to 12 percent effective when located away from the duct wall. For under expanded flows at NPR 8.5 the base drag reduction was between 49 and 64 percent depending on the location of the controller. Also, the control did not adversely affect the flow field. Further flow visualization inside the duct was captured using a shadowgraph.