  We perform direct numerical simulations of laminar separated flows over
finite-aspect-ratio swept wings at a chord-base Reynolds number of $Re = 400$
to reveal a variety of wake structures generated for a range of aspect ratios
($sAR=0.5-4$), angles of attack ($\alpha=16^{\circ}-30^{\circ}$), and sweep
angles ($\Lambda=0^{\circ}-45^{\circ}$). Flows behind swept wings exhibit
increased complexity in their dynamical features compared to unswept-wing
wakes. For unswept wings, the wake dynamics are predominantly influenced by the
tip effects. Steady wakes are mainly limited to low-aspect-ratio wings.
Unsteady vortex shedding takes place near the midspan of higher-$AR$ wings due
to weakened downwash induced by the tip vortices. With increasing sweep angle,
the source of three dimensionality transitions from the tip to the midspan. A
pair of symmetric vortical structures forms along the two sides of the midspan,
imposing downward velocity upon each other in a manner similar to the downwash
induced by tip vortices. Such stabilizing midspan effects not only expand the
steady wake region to higher aspect ratios, but also enhance lift. At higher
aspect ratios, the midspan effects of swept wings diminish at outboard region,
allowing unsteady vortex shedding to develop near the tip. In the wakes of
highly swept wings, streamwise finger-like structures form repetitively along
the wing span, providing a stabilizing effect. The insights revealed from this
study can aid the design of high-lift devices and serve as a stepping stone for
understanding the complex wake dynamics at higher Reynolds numbers and those
generated by unsteady wing maneuvers.
