Performance Analysis of High Frequency Oscillating Circulation Control

A design for Coanda-type circulation control effectors allowing for continuously variable control of the flow direction is presented. The design requires only a single plenum for multi-directional (up/down) control. Performance of the control effector is measured using a device installed in a symmetric NACA-0015 airfoil in the Andrew Fejer Unsteady Wind Tunnel. The Coanda effectors are operated at discrete frequencies ranging from 0.25 Hz to 5 Hz, which correspond to dimensionless frequencies k = 0.0094 to 0.31, where one cycle of the effector is defined to be maximum upward blowing, to maximum downward blowing, back to maximum upward blowing. Smoke-wire flow visualization, force balance measurements, and particle image velocimeter measurements were acquired to characterize the directional control of the Coanda control effector. The directional control allowed for a continuous range of motion between upward, neutral, and downward blowing, and the resulting control effect is comparable to conventional designs that have fixed blowing directions. The decrease in lift increment performance with increased frequency was measurable, and indicated a -3dB reduction at k = 0.2. In the dynamic sweeping case for a range of angles around the neutral blowing angles, the actuator demonstrates a measurable decrease in drag. Increasing control authority was found with increasing Reynolds number.