Control of a Semi-Circular Planform Wing in a "Gusting" Unsteady Freestream Flow: I - Experimental Issues

Abstract

Active flow control is used to modify the lift, drag and pitching moments on a semicircular wing during "gusting" flow conditions. A longitudinal oscillating flow component has an amplitude of 10 percent of the freestream speed and a frequency giving k = 0.048 (f = 0.2 Hz). The aspect ratio of the wing is AR = 2.54, and the chord Reynolds number of the wing is 70,600. Pulsed-blowing flow control actuation occurs along the leading edge of the airfoil via 16 spatially localized micro-valve actuators. Feed-forward control based on a quasi-steady lift model is used to stabilize lift fluctuations generated by an oscillating free stream, which simulates the longitudinal component of a gusting flow. The quasi-steady system model reduces the amplitude of the fundamental and first harmonics of lift oscillations, but does not account for time delays. The time delay between the lift and the freestream oscillation was measured to be τ_(u)^(+) = 4.8. The time delay between the lift and the actuator input signal was found to be τ_(a)^(+) = 11.3.

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