Identification of critical perturbation amplitudes for control of a finite, wall-bounded wing at transitional Reynolds numbers

The performance of wings at transitional Reynolds numbers is strongly influenced by the dynamics of laminar separation and reattachment, particularly the possible existence and location of shear-layer transition and subsequent reattachment. The sensitivity of these flows to small perturbations also makes them appealing for control. Wind tunnel experiments are performed on a finite, NACA 65(1)412-section wing, aspect ratio AR = 3, placed between two end walls. An array of speakers is embedded within the wing for active control, and both force data and particle image velocimetry-derived flow fields are collected. It is found that under conditions enabling an open laminar separation, there is a critical amplitude of excitation for which the shear layer is destabilized sufficiently to reattach, causing a jump in performance metrics. These perturbation amplitudes are identified for varying actuator positions, representing an empirical estimate of the spatial growth of perturbations. Agreement with predicted growth rates from linear stability analysis as well as growth of fluctuations from direct numerical simulations of the base flow is evaluated.