Abstract
Dynamical characteristics of tip vortices shed from a 1 m diameter, four-bladed rotor in hover are investigated using various aperiodicity correction tech- niques. Data are acquired by way of stereo-particle image velocimetry and comprises measurements up to 260 vor- tex age with 10 offsets. The nominal operating condition of the rotor corresponds to Rec = 248,000 and M = 0.23 at the blade tip. With the collective pitch set to 7.2 and a rotor solidity of 0.147, blade loading (CT/r )i s estimated from blade element momentum theory to be 0.042. The findings reveal a noticeable, anisotropic, ape- riodic vortex wandering pattern over all vortex ages mea- sured. These findings are in agreement with recent observations of a full-scale, four-bladed rotor in hover operating under realistic blade loading. The principal axis of wander is found to align itself perpendicular to the slipstream boundary. Likewise, tip vortices trailing from different blades show a wandering motion that is in phase instantaneously with respect to one another, in every direction and at every wake age in the measurement envelope.
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