Swallow-tailed separation bubble on a low-aspect-ratio trapezoidal plate: effects of near-wall spanwise flow

The three-dimensional flow over a low-aspect-ratio (low- $A\!R$ ) trapezoidal plate is investigated experimentally with focus on how the tip effects impact structure and dynamics of separation bubble. chord-based Reynolds number $5800$ , angle attack varies from $4^\circ$ to $10^\circ$ . Once separates, bubble emerges features swallow-tailed that shrinks near midspan, which first found for flows low- plates. This develops into conventional single-tailed as increases. Moreover, vortex shedding within restored multiple asynchronously measured local velocity fields. It revealed leading-edge undergoes novel transformation C-shape an M-shape vortex. stems mass transport near-wall spanwise flow, affects fluid motion windward side head, strengthening accelerating head. strengthened head facilitates entrainment high-momentum outer flow. responsible formation structure. These findings help fill gaps left by downwash at low angles wings, are value in improving cruising gliding performance micro-air vehicles.