Nature of Wakelike and Jetlike Axial Tip Vortex Flows

The mechanisms responsible for the wakelike and jetlike axial flows of a tip vortex were investigated experimentally at Re = 3.07 x 10(5). Both square and round tips were tested. Along the wing tip, a pocket of a higherthan-freestream, or jetlike, fluid was continually present, regardless of the tip condition and airfoil angle of attack a. Its maximum velocity increased with a and always exhibited a peak value around the trailing edge. In the near field, this jetlike fluid pocket was entrained by the shear layers and the wing wake, and it resulted in a wakelike axial flow for smaller a. For higher a, the jetlike fluid pocket was, however, surrounded by the shear layers that, in turn, protected it from the destructive effects of the wing wake and remained jetlike. The switchover angle at which the axial flow switched from wakelike to jetlike appeared around 7 deg, regardless of the tip condition, which also coincided with the angle at which the lift-to-drag ratio was a maximum. Finally, the round-tip-produced vortex was more concentrated and had a higher peak tangential velocity and core circulation but a smaller core radius compared with those of the square tip.