A Full-Scale Particle Image Velocimetry Investigation of “Young” Rotor Blade Tip Vortices

Abstract

The blade tip vortex of a full-scale MBB Bo 105 Helicopter is investigated experimentally under simulated hover flight conditions in ground effect by means of stereoscopic Particle Image Velocimetry. Based on the three-component velocity field of azimuthal vortex ages of y=1°, 3°, 5°, 10°, 20° and 30° vortex core radii, peak velocities, and vorticities are quantified and compared to model-scale experimental results available in literature and Vatistas’ low-order model for concentrated vortices. The vortex velocity profiles are found to be in satisfactory agreement with the model whereas the experimentally limited spatial resolution of the velocity fields results in a slight overestimation of the core radii and an underestimation of peak velocities as compared to model-scale investigations. Finally, an attempt has been made to cross-validate full-scale blade tip vortex parameters derived from Background Oriented Schlieren measurements using natural formation backgrounds.