The reduction of side force acting on a cone-cylinder slender body using a microballoon array actuator is examined. This microballoon array actuator can be inflated to a height of approximately 1.2 mm on the curve surfaces of the slender body. Experimental results indicate that side forces can be significantly reduced by inflating actuators near the weak and strong separated vortex structures. The mechanism of side force reduction has been investigated via both hot-wire and surface pressure measurements. Interestingly, unlike the conventional methods of changing the vortices from asymmetric to symmetric pairing for side force reduction, a microballoon array actuator makes vortices more asymmetric. It was found that two mechanisms can characterize the reduction of side force. The first mechanism involves that the weak side vortex lifts off prematurely because the microballoon actuation replaces the vortex pair structures with a more asymmetrically positioned pattern, enabling the formation of a new (third) vortex in the near-wall region. The second mechanism involves the strength of the newly generated (third) vortex being able to be effectively controlled via the microballoon actuation. Microballoon actuators can effectively alter the evolution of the new (third) near-wall vortex structure.
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