MEASUREMENTS OF THE VELOCITY AND TURBULENCE STRUCTURE OF A ROTOR TIP VORTEX

The turbulent how structure of a tip vortex generated by a hovering ro tor was investigated with the use of three-dimensional laser Doppler v elocimetry. The velocity field was measured at five wake ages, with th e three components of turbulence being measured at the three earliest ages. The tangential (swirl) velocity component inside the tip vortex was found to have a self-similar behavior for all wake ages. The visco us core size was estimated to be approximately 2.5% of the blade chord just after formation, growing with the square root of vortex age to a bout 13% of blade chord at one rotor revolution. At early wake ages, r adially symmetric peaks in the turbulence intensities were measured in side the vortex core, whereas only a single peak appeared in the turbu lence distribution at later ages. The radial component of turbulence w as found to be the most dominant, with the axial component being the s mallest. Additional turbulence quantities, such as Reynolds' stress, w ere also measured. Finally, the evolutionary features of the turbulent kinetic energy production are discussed.