Computational investigation of quiet propeller designs for small unmanned aerial vehicles

Abstract

The noise produced by the propellers of micro Unmanned Air Vehicles (UAVs) could be counterproductive to their mission, since adversaries can often hear them from a distance. This study investigates new quiet propeller designs that have different twist angle distributions that vary the lift generated along the span of the propeller blade to reduce the thrust loading near the tip. In addition, nine co-rotating dual propellers with different phase angle and spacing are considered. All propellers were tested at the USAFA subsonic wind tunnel at an assumed UAV cruise velocity of 44 ft/s while measuring thrust, torque, sound pressure level, and rotational speed over a range of power settings. These propellers are modeled using the DoD HPCMP CREATETM-AV Kestrel simulation tools. The thrust and torque were extracted from these simulations and compared with experimental data. Pressure tap points were defined one inch behind the propeller. The instantaneous pressure data were measured at these locations for 20 spinning cycles. Sound pressure level values were then estimated from these data. Predictions are then compared with experimental data measured from a traversing microphone.