Acoustic and Flowfield Measurements of Rotor-Surface Interaction

Effects of flow interactions between a rotor and a rectangular plate are investigated experimentally. Acoustic data collected show an increase of up to 5 dB in tonal noise at downstream observer locations for configurations with the plate. High-speed particle image velocimetry data show reduced velocity magnitudes in the rotor downwash near the blade location, increasing static pressure at the bottom surface of the blade, and inducing loading fluctuations as the blade passes over the plate, which are associated with the increase in tonal noise. Decreased broadband noise values at downstream observer locations indicate acoustic shielding effects due to the presence of the plate. The interaction between the blade tip vortices and the shear layer generated at the edge of the plate generates greater fine-scale turbulent kinetic energy downstream of the flow. No increases in broadband noise caused by this interaction are observed in the acoustic data.