Motion-Induced Unsteady Aerodynamic Loads with Development of Vortical Flow

Abstract

The development of vortical flow strongly changes the properties of motion-induced aerodynamic loads. Tests were performed in the Transonic Wind Tunnel Göttingen with a half-wing model of a lambda wing. A hydraulic actuator imposed pitch oscillations with amplitudes and frequencies relevant for aeroelastic analyses. Unsteady surface-pressure and flowfield measurements were performed. With increasing angle of attack, a leading-edge vortex emerges and moves inboard. The unsteady loads show a strong dependency on the effects of the vortical flow. For the pitching cases, the effects are lagging the motion. In the rear outboard part of the wing, the unsteady pressures are small, but the amplitude of the motion is high. Hence, a significant amount of energy—force integrated over motion—is transferred from the fluid to the motion. For a free motion or deformation of the wing, this would cause a destabilization. A significant effect of the vortical flow is the discrepancy between the position where it emerges and is affected, and the position (e.g., further outboard) where the flow may generate unsteady, potentially destabilizing loads.