Interaction of quasi-two-dimensional vortical gusts with swept and unswept wings

Water tunnel experiments were conducted to study the interaction of gusts with swept and unswept finite wings set at zero angle of attack. Single vortex filaments were generated by plunging an upstream airfoil at zero angle of attack in transient motion. The vortex filament, which was initially quasi-two-dimensional, deformed, diffused, and lost coherency as it interacted with the wing. The details of the interaction were documented by means of phase-locked force measurements and particle image velocimetry (PIV) measurements in multiple spanwise planes. Phase-locked PIV measurements show trajectory deflection, vortex diffusion, and flow separation over the wing. For the swept wing, the local structure of the vortex only depends on the relative location of the wing cross-section at that particular spanwise plane. The results show that when the counterclockwise vortex passes the wing in proximity, the lift coefficient CL exhibits a sharp rise followed by a sharp decrease to negative values before recovering to zero.