Lift disturbance cancellation with rapid-flap actuation

Mitigation of vertical aerodynamic disturbances by means of a simple mechanical flap is investigated experimentally. A wall-to-wall NACA 0006 wing is bisected about the midchord for a 50%-chord flap length. Experiments are performed in a water tunnel at a chord-based Reynolds number of Re 4 × 10⁴ . The wing is driven in a sinusoidal vertical plunge motion as a spatially uniform, temporally varying surrogate to a vertical disturbance. Concurrently, the flap is actively deflected in a survey of kinematic parameters designed to suppress the influence of a plunge-induced disturbance. Plunge rates explored amount to disturbances incurred over a temporal range from one convective time to eight convective times. Two methodologies are employed to guide selection of flap deflection phase and amplitude necessary to preserve the baseline zero-lift state (α 0°) of the undisturbed wing. In the first method, Theodorsen’s model is applied to arrive at an analytical solution to flap kinematics for a given prescribed plunge history. The theoretical derivation makes the standard assumptions of attached flow, planar wake, and no leading-edge vortical formations. Direct force measurements reveal reduction in lift transients by flap actuation of up to 87%, verifying the applicability of Theodorsen’s classical model. Further improvement is sought in a second method where empirical state-space modeling is formulated for lift cancellation. In this approach two separate lift models for wing plunge and flap deflection are constructed independently, and their superposition is employed to approximate the total lift in combined plunge and deflection motions. It is shown that although the empirical state-space approach performs similar to the inviscid theory of Theodorsen’s model, the empirical model proves more effective in suppressing the formation of the leading-edge vortex induced by plunge.