The movement, structure and breakdown of trailing vortices from a rotor blade

TLDR: In this paper, the results of some flow visualization experiments on the trailing vortices from a model rotor blade are presented, and it is found that, at low tip-speed ratios, the trailing vortex close to the leading edge of the disc first pass up through the disc before entering the main flow field.

Abstract: : The results of some flow visualisation experiments on the trailing vortices from a model rotor blade are presented. It is found that, at low tip- speed ratios, trailing vortices close to the leading edge of the disc first pass up through the disc before entering the main flow field. At the rear of the disc the vortices maintain a regular pattern relative to each other. The vortices are fully rolled up in about 60 deg of azimuth movement of the blade. Measurements with a hot-wire anemometer show that the vortex core is about one- tenth of a blade chord in diameter, which is consistent with a laminar core state. Outside the core the velocity field is irrotational. Some observations were made of a trailing vortex as it approaches the support pylon. The vortex at first follows the pylon contours and remains a tightly-rolled core, but it ultimately leaves the pylon surface and its structure breaks down, rather like the vortices from the leading edges of a delta wing.