An examination of blade-vortex interaction utilizing pressure measurements and particle image velocimetry

Under certain conditions of powered descent or vigorous maneuvering, rotorcraft blades pass through the wake and trailed tip vortices from previous blades. This interaction of the rotor blade with the tip vortex of a preceding blade has been identified as a significant source of noise and vibration in rotorcraft. The need to reduce these undesirable effects requires that the rotorcraft designer has a clear understanding of the fluid dynamics underlying the phenomena of blade-vortex interaction (BVI). To provide this understanding a simple empirical model of the three-dimensional flow structures generated during blade-vortex interaction is presented.;The present model of the blade-vortex interaction flow field is developed from a consideration of the effects of the three-dimensional distribution of vorticity about the blade. The three-dimensional vorticity distributions incorporated in the model include the vorticity in the interaction vortex, the vorticity trailed from the blade tip, the vorticity shed from the blade, and the vorticity trailed from lift discontinuities along the blade span. These vortical structures are examined independently, with the net effect upon the blade depending upon the three-dimensional arrangement of these structures in the vicinity of the blade.;This empirical BVI model is based upon experimental data collected in a series of wind tunnel tests at the University of Glasgow. In the first set of tests pressure measurements were made about the blade during interactions. These pressure measurements were used to provide unsteady pressure profiles about the blade, and the histories of unsteady force and moment coefficients integrated from the pressure profiles. In the second set of tests Particle Image Velocimetry (PIV) was used to measure the velocity field about the blade during interactions. The expected effects of the various vortical structures comprising the model are found consistent with all of the main features of the data from both sets of experiments.