Sweeping jet control of flow around a circular cylinder

An experimental investigation was conducted to examine the control effectiveness and mechanism of sweeping jets in the control of vortex shedding from a circular cylinder. Wind tunnel experiments were performed at a Reynolds number of 3.2 x 104. Two rows of sweeping jet actuators were arranged symmetrically at positions 70 degrees clockwise and counterclockwise from the front stagnation point. Five operating conditions with different mo-mentum coefficients were tested. Particle image velocimetry was used to measure the detailed flow structures of the uncontrolled and controlled cylinders. With increasing jet strength, the control performance improved non -monotonously. With a relatively small momentum coefficient of less than 0.0086, the sweeping jets enlarged the recirculation bubble in the wake of the cylinder. However, with larger momentum coefficients, the sweeping jets reduced the size of the recirculation bubble by modifying the wake shear layer and pushing the vortex shedding toward the centerline. When the momentum coefficient was increased to 0.2147, sweeping jet control achieved a 73 % decrease in turbulence kinetic energy and a 68 % decrease in the normalized Reynolds shear stress compared with the uncontrolled case. The control effectiveness was similar can be observed at different spanwise planes. Instantaneous pressure measurement showed that with sweeping jet control, the amplitudes of the fluctuating force acting on the cylinder caused by unsteady vortex shedding were reduced by 94 % compared with the uncontrolled case. Proper orthogonal decomposition analysis showed that when the momentum coef-ficient was 0.2147, a novel flow pattern occurred in which one vortex grew larger while the other shrank in a relatively steady wake region.