Investigation of tip vortex formation, development and merging using particle image velocimetry (PIV) technique

One of the aims of this thesis is to investigate the details of the formation, structure and development of the wing tip vortices. Particle image velocimetry technique was used as a measurement technique for all experiments. Experiments have been carried out at different angle of attacks which affect the vortex strength, size and tangential velocity at different downstream stations. The growth of tip vortex along the chordlength with increasing attack angle is determined. The characteristics of the trailing vortices have been investigated by means of qualitative dye visualization and quantitative velocity measurements using PIV methods. The experiments have also been carried out at attack angle of 7°. The strength, size and tangential velocity of the vortex, vorticity distribution and circulation of trailing vortices have been calculated at different downstream stations. The effect of the flow behavior at the tip along the spanwise of the wing has been investigated by using PIV technique. Measurements were carried out at different stations and attack angles (?=0° ~ 16°). It is concluded that the flow structure near the tip was affected considerably from the tip vortex. Tip vortex strength increases with increasing attack angle. The effect of tip vortex also increases with increasing attack angle in spanwise direction. Three dimensional flow structures were observed close to the wing tip. Away from the tip, two-dimensional flow structure around the wing was obtained. Finally, vortex merging of two co-rotating vortices has been investigated. Experiments have been performed at different cross-sections downstream of the wing tip. Co-rotating vortices which occur at the wing tips, first of all, intersects each other at a distance of x/c=10, then, two co-rotating vortices merge at x/c=20 behind the wing trailing edge. The quantitative results are presented with time-averaged vorticity, velocity and streamline topology. Keywords: PIV, NACA0012, tip vortex, vortex merging