Study on Unsteady Aerodynamic Characteristics and Flow Field Evolution of a Flapping-Wing Vehicle during Turning Maneuvers

Abstract

To reveal the unsteady aerodynamic responses and flow field reconstruction of bionic flapping-wing vehicles during complex maneuvers, a vehicle driven by a spatial crank-rocker mechanism was investigated. Using ANSYS Fluent integrated with UDF and overset grid techniques, the spatio-temporal coupled flight transition from level flight to a 90˚ crosswind sharp turn was simulated. Analysis of the aerodynamic loads and three-dimensional vortex topology visualized using the Q-criterion over six consecutive flapping cycles reveals that, during turn initiation, the outer wing maintains a strong attached leading-edge vortex (LEV), while the pressure imbalance between the two wings generates rolling and yawing moments toward the turn center. During sustained turning, the curved flight trajectory induces lateral bending of the wake vortices. A large sideslip angle leads to aerodynamic decoupling between the windward and leeward wings, with fuselage shielding causing LEV detachment from the leeward wing. Under the limiting condition of a 90˚ sideslip angle, crossflow produces high-pressure regions over the upper surfaces of both wings ( 0 P ∆ < ), resulting in substantial negative lift. The organized spanwise vortices break down, giving way to large-scale bluff-body separation and deep stall. These findings elucidate how extreme crosswinds degrade flapping-wing aerodynamic performance and provide insights into control-law design and aerodynamic shape optimization for flapping-wing aircraft.