Lift Distributions For A 3-Dimensional Steady Blade-Vortex Interaction

An experimental investigation simulating a helicopter rotor blade-vortex interaction has been conducted in the NASA Ames 7 x 10-Foot Wind Tunnel. The objective of this investigation was to document blade loading for the interaction and to examine changes in loading induced by variations in vortex strength and position. The experimental configuration consisted of a semispan vortexgenerating wing mounted vertically from the tunnel ceiling upstream of a horizontally mounted semispan wing that is representative of a rotor blade. The tip vortex from the vortex generating wing was convected downstream past the rotor blade tip to generate an interaction of the type often encountered for helicopter rotors in hover or slow descent. A three-dimensional laser velocimeter (3-D LV) was used to measure the velocity field in the region of the blade. The spanwise lift distribution on the blade was calculated from line integration of the velocity around the blade to evaluate the bound circulation. Total lift was measured with an internal strain-gage balance to validate the LV data. Experimental parameter variations included vortex strength, rotor blade angle of attack, and vortex position relative to the rotor blade. Flow predictions computed with a contemporary panel method code (VSAERO) are compared with the experimental data. The study provides detailed lift distribution data for a simulated 3-D steady blade-vortex interaction and evaluates the ability of a current potential-flowprediction technique to accurately model this interaction.