Flow Visualization of a Wingtip Using Rotation and Sweep for Gust Mitigation

Flow visualization is used to study a high-angle-of-attack flat-plate wing with a rotating, swept tip panel for gust mitigation. Towing-tank experiments emulate two streamwise gusts: step-up to 50% higher speed and step-down to 50% lower. The rectangular main-wing aspect ratio is 4 at a 45 deg angle of attack. To alleviate step-up gusts, the swept panel rotates inward in-plane to reduce lift, and for step-down it starts retracted and then actuates outward for greater lift. The unsteady flow is studied using dye visualization to explain the lift behavior. The step-up gust generates a new leading-edge vortex (LEV), like a starting flow. Wingtip actuation-in lowers the lift coefficient longterm, below the rectangular and swept cases, by shedding the panel’s swept-edge vortex (SEV) through locally reversed flow and weakening the outboard, attached LEV via inboard flow. Actuation-in also lowers the drag. For step-down gusts, the wake impinges on the decelerating wing, spreading the wake outward and increasing the wake angle, which reduces lift. The actuation-out creates an attached SEV that partially mitigates the gust’s negative lift peak. A helical LEV develops outboard flow, causing a lift-recovery plateau or rise; actuation-out initially performs best. The spanwise flow later switches to be inboard, causing LEV growth and shedding.