Vortex Structure Investigation by LDV for Two Rotor Blade Tips in Forward Flight

Kurzfassung

The measurement of local flow vectors at positions near the helicopter rotor were performed with a three component Laser- Doppler-Velocimeter (3D LDV). The new conception of 3D-LDV brought good progress concerning sensitivity, data rate and third component resolution. A position monitoring system gave access to blade motion parameters (lead-lag motion, pitching and angle of incidence) at any chosen radial position of the blade, where LDV measurements were performed. The measurements gave principle results concerning the structure of a blade tip vortex in forward flight condition. For example the vortex core radius has been obtained as well as the speed of vortex roll up. Since the tests were run with two different blade tips, a regular square tip for reference and a non-planar tip called winglet, the influence of these winglets on vortex structure and BVI behaviour was investigated. In addition to the vortex parameter like location of the 3D-LDV measurements yield results concerning the orientation of the vortex axis in space, 3D-vorticity and the temporal roll up of the different blade tip vortices.