Triglobal resolvent-analysis-based control of separated flows around low-aspect-ratio wings

We perform direct numerical simulations (DNS) of actively controlled laminar separated wakes around low-aspect-ratio wings with two primary goals: (i) reducing the size of the separation bubble and (ii) attenuating the wing tip vortex. Instead of preventing separation, we aim to modify the three-dimensional (3-D) dynamics to exploit wake vortices for aerodynamic enhancements. A direct wake modification is considered using optimal harmonic forcing modes from triglobal resolvent analysis. For this study, we consider wings at angles of attack of 14^ and 22^, taper ratios 0. 27 and 1, and leading edge sweep angles of 0^ and 30^, at a mean-chord-based Reynolds number of 600. The wakes behind these wings exhibit 3-D reversed-flow bubble and large-scale vortical structures. For swept and tapered wings, the diversity of wake vortices increases substantially, posing a challenge for flow control. To achieve the first control objective, a root-based actuation at the shedding frequency reduces the reversed-flow bubble size and capitalizes on wake vortices to significantly enhance the aerodynamic performance of the wing. For tapered and swept wings, actuation modifies the stalled flow, increasing the root contribution to lift. For the goal of controlling the tip vortex, we demonstrate the effectiveness of actuation with high-frequency perturbations near the tip. This study shows how insights from resolvent analysis for unsteady actuation lead to the global modification of 3-D separated wakes and improved aerodynamics of wings.