Effects Of Modifying A Rotor Tip Vortex By Injection On Downwash Velocities, Noise, And Airloads

Numerous research efforts have been conducted by different investigators to alter the characteristics of the tip vortex generated by a helicopter blade in order to alleviate the blade-vortex interaction problem as well as the noise problem associated with impulsive loading. Various approaches have been taken in these investigations including modifications of the loading distribution by taper and twist and altering the blade tip by utilizing porous sections. All of these approaches have not been universally successful for all flight conditions. The present analytical investigation shows that it should be possible to significantly alter the characteristics of the trailing tip vortex for almost all flight conditions in a beneficial manner by injecting an airstream directly into the forming tip vortex. Analytical expressions were developed for the initial and final states of the vortex in order to evaluate the effects of mass flow injection on the vortex strength, swirl velocity distribution, vortex core pressure, vortex core size and the induced drag on the blade.