Dynamical and Evolutionary Characteristics of the Tip Vortex from a Four-Bladed Rotor in Hover

The dynamical and evolutionary characteristics of the tip vortices produced by a reduced-scale, 1m diameter, four-bladed rotor in hover are investigated using the well known Q criterion combined with the center of mass (C-o-M) approach. The data is acquired by way of stereo PIV and focused on wake ages up to 360° with 10° offsets during hover conditions. The nominal operating condition of the rotor is at a rotational speed of 1520 RPM, corresponding to Rec = 248,000 and a blade loading of CT /σ = 0.0446, obtained from BEMT estimates. Previous investigations revealed a noticeable, anisotropic, aperiodic vortex jitter pattern over all vortex ages which was not previously observed. Furthermore, the core radius appeared to be constant after the first blade passage, even up to a vortex age of 260° and was also not previously observed. These findings are confirmed using other vortex methods: Centroid of Vorticity and Normalized Helicity.