The role of swept wing-tail interactions in dipole jet formation during stopping flows

In low speed stopping flights, birds often execute rapid pitch-up motions in a decelerating flow combined with wing sweep to generate unsteady forces through leading-edge vortices (LEVs). These LEVs, interacting with trailing-edge vortices (TEVs), form dipole jets that enhance unsteady forces during deceleration. However, the role of tail-wing interactions in modulating these vortex structures remains poorly understood, particularly for low aspect ratio wings at low Reynolds numbers. In this study, we investigate how main-tail wing interactions influence dipole jet dynamics and force generation during perching-like maneuvers. Using four bio-inspired wing configurations—straight and swept-back wings, with and without tails—we conducted towing water tank experiments at Re = 7500 using PIV and force measurements. Our results reveal that swept-back wings with tails generate stronger unsteady forces and exhibit intensified vortex interactions between the main and tail wings. These findings underscore the aerodynamic importance of wing-tail coupling in enhancing unsteady forces and control during rapid stopping maneuvers.