Investigation into the Rollup and Diffusion of Rotor Tip Vortices using Laser Doppler Velocimetry

Phase-resolved three-component laser Doppler velocimetry measurements were made in the wake of a hovering rotor. The overall objectives of the work were to gain a deeper understanding of the tip vortex formation from rotor blades, and to help document their diffusive and dissipative characteristics. Experiments were performed on both one and two-bladed rotors. Particular emphasis was placed on measuring the vortex core size, the tangential (swirl or circumferential) and axial profile distributions, and the effects of blade passage on the vortex development. Measurements of bound circulation over the blade are also discussed. Finally, the quantitative effects of seed particle size and flow aperiodicity on the measurements are documented.