  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 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 $14^\circ$ and $22^\circ$, taper ratios $0.27$ and $1$, and
leading edge sweep angles of $0^\circ$ and $30^\circ$, 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 tapered swept
wings, the diversity of wake vortices increases substantially, posing a
challenge for flow control. To achieve the first control objective for an
untapered unswept wing, root-based actuation at the shedding frequency is
introduced to reduce the reversed-flow bubble size by taking advantage of the
wake vortices to significantly enhance the aerodynamic performance of the wing.
For both untapered and tapered swept wings, root-based actuation modifies the
stalled flow, reduces the reversed-flow region, and enhances aerodynamic
performance by 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 can enable global modification of
$3$-D separated wakes and achieve improved aerodynamics of wings.
