Control of the unsteady, separated flow behind an oscillating, two-dimensional flap

Abstract

Methods of passive and active open-loop control of the unsteady, separated flow produced downstream of a two-dimensional lifting flap have been examined. Phase-averaged, unsteady pressure measurements were used to measure the effect of the control on both the unsteady vortex formed as the flap lifts from the tunnel floor and the steady separation formed when the flap remains in the vertical position. The passive control experiments used twc- and three-dimensional disturbances upstream of and at the separation line located at the trailing edge of the flap. Due to the fixed separation line of the flap, the unsteady vortex was not changed by the passive control, however significant increases were obtained in the pressure recovery for the steady separation. Using pulsed blowing and suction, the active control experiments were able to reduce the suction peak of the unsteady vortex by as much as 40% and delay the peak suction by 14 milliseconds in addition to increasing the pressure recovery in the steady separation. A simple model for estimating the x-position, y-position, and circulation of the unsteady vortex using the measured pressures shows good agreement with vortex properties calculated using detailed velocity measurements.