Surface Pressure Measurements of the Orthogonal Vortex Interaction

Abstract

A unique vortex generator that simulates the trailing vortex produced by a helicopter main rotor in forward flight was used in a study of main rotor/tail rotor blade vortex interaction. Velocity measurements were performed using hot wire anemometry and particle image velocimetry, which showed the interacting vortices to be three dimensional and to contain a significant core axial flow. Surface pressure measurements during vortex collision with an instrumented, stationary blade were obtained at a variety of incidence settings. At the leading edge, a suction peak occurred where the core flow was directed away from the surface and, similarly, a pressure peak occurred where the core flow was directed toward the surface. This behavior can be explained in terms of the impulsively blocked vortex core axial flow. Also, the leading edge suction and pressure peaks were amplified or attenuated by changing the incidence of the blade. However, the changes in surface pressure distribution were such that the peak normal force was approximately the same for each incidence setting.