Flow Field Investigation of a Rotating Helicopter Rotor Blade by Three-Component Laser-Doppler-Velocimetry

The measurement of three dimensional local flow vectors of a blade tip vortex at positions near the helicopter rotor plane were performed with a three component laser-Doppler-velocimeter (3D LDV). A 'possition monitoring system' synchronized to the blade rotation gave access to blade motion parameters like lead-lag and pitching at the desired radial position of the blade. Mainly results concerning the structure of blade tip vortices were obtained. The measurements of a vortex generated at hover condition showed the correctness of 'time history' data acquisition, e.g. taking data during the time interval when one particular blade is passing the location of the measuring volume of the LDV