Abstract:
High-resolution particle image velocimetry measurements were taken to document the initial roll-up and evolution of the tip vortices trailed from a rotor operating in ground effect with pumping rotor blades. The pumping blade design utilized an internal duct connecting the intake slot near the root of the blade with exit slots at the blade tip. The baseline non-pumping and pumping blades were tested in a hovering state in ground effect at a blade loading coefficient of 0.080. Performance measurements were taken both out of ground effect and in ground effect to examine the effect of the Coriolis torque generated by the pumping blades. A first-order theoretical investigation of the Coriolis torque was performed using a one-dimensional, incompressible, fully developed, steady flow analysis on the flow through the internal duct. The method yielded a simple equation that was determined to be highly dependent on the assumed conditions of the internal flow (e.g., laminar, turbulent, etc.). The spanwise blowing of the pumping blades initially generated a vortex core that was significantly more distorted than the baseline blade but this initial distortion was overcome by the rotation of the vortex. Furthermore, the pumping blades produced significantly more diffused tip vortices, producing peak swirl velocities approximately half that of the vortices produced by the baseline blades.