Interactions of Propellers in Edgewise Flight with Turbulence

Experiments were conducted to establish the impacts on the aerodynamics and aeroacoustics of propellers ingesting turbulent flow within edgewise flight conditions. A single, 2-bladed propeller with a low pitch-to-diameter ratio was tested within an aeroacoustic wind tunnel facility at free-stream velocities ranging from 0-15.6 m/s and at rotational rates of 7500 RPM and 12000 RPM. Two passive turbulence grids were manufactured and tested to generate turbulent flow. Velocity data were collected using hot-wire anemometry to characterise the turbulent flow generated by each grid at the wind tunnel nozzle outlet. The effects of different turbulent length scales and intensities on propeller performance was investigated. The thrust and torque data, as well as the radiated far-field noise for each case were collected. The turbulence generated by the grids shows evidence of interactions with the propeller, leading to highly directive changes in the acoustic far-field. The results indicate that a larger turbulence intensity and integral length scale will lead to stronger interactions with the propeller, in some cases leading to haystacking of the blade-passing-frequency tonal peaks. Overall, the grid generated turbulence interactions lead to overall sound pressure level increases in the acoustic far-field.