Experimental study on the tip vortices of a wing close to a flat and a wavy surface using PIV

An experimental study on the tip vortices and lift/drag forces of a NACA23012 wing in adjacent to the flat and the sine wavy surface at zero angle of attack is introduced. The experiment is conducted in a towing tank. The study focuses on the hydrodynamics and evolution of the tip vortices of the wing close to the flat and the sine wavy surface with different ground height, velocity and vorticity distribution, as well as their influence on the lift/drag force of the wing are compared. The results show that, the lift force decreases from positive to negative as the wing gets closer to the wavy surface, the intensity of the tip vortices change as well, and the shape of tip vorticesis is deformed correspondingly. Especially, for the case of small ground height and negative lift force, the rotation direction of the tip vortices is changed. The flow structure is not only affected by the wing ground height, but also influenced by the phase relation of the wing and the ground, i.e. the instantaneous shape of the flow channel between the lower surface of the wing and the wavy ground surface. And the vorticity of the tip vortices along the wavy surface presents some periodic variation, whereas the variation does not comply with sine regularity. The reason is that the periodical variation of the shape of the flow channel and the stenosis degree of the channel beneath the wing brings a different level of inhabitation to the evolution of the tip vortices.