Particle Image Velocimetry Measurements and Performance Analysis of Rotors with Slotted Blades

Abstract

Particle image velocimetry measurements were taken to document the initial formation of the tip vortices trailed from a rotor operating in ground effect with pumping rotor blades. The pumping blade design used an internal duct connecting the intake slot near the root of the blade with exit slots at the blade tip. The baseline nonpumping and pumping blades were tested in a hovering state at a blade loading coefficient of 0.08. Performance measurements were taken both out of ground effect and in ground effect to quantify the additional power requirements associated with the pumping blades. A first-order analysis was performed assuming one-dimensional, incompressible, fully developed, steady flow through the internal duct. The method yielded a simple equation that was dependent on the assumed conditions of the internal flow through the duct (laminar, turbulent, etc.). The flow field measurements showed that 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 generated significantly more diffused tip vortices, producing peak swirl velocities approximately half that of the vortices from the baseline blades.