A Study of the Aeroacoustics of Swept Propellers for Small Unmanned Aerial Vehicles

In recent years, small unmanned aerial vehicles (UAVs) have increased in availability and use in both public and commercial sectors. This increased use of small UAVs or “drones” has the unfortunate consequence of introducing excessive noise into communities where they operate. Implementation of noise reduction methods is necessary if we wish to see expanded use of drones in public areas. With electric propulsion, the primary source of noise is the rotor/propeller used in contemporary multi-rotor configurations. In this thesis, the aerodynamics and acoustic behavior of various swept propellers is examined with computational and experimental methods. A family of propeller geometries was established, with test articles machined from aluminum. A straight 16x11.363-inch propeller was used as a control for the nonconventional 15, 35, and 55 degree swept propellers. These propellers have a backwards sweeping blade centerline designed to “de-phase” the far-field acoustic pressure. The aerodynamic properties were collected in ODU’s low speed wind tunnel and an acoustic experiment was conducted outdoors to determine the noise characteristics of the propeller while hovering. The computational analysis was done with NASA’s Aircraft Noise Prediction Program 2 (ANOPP2). This program used the Farrassat-1A Formulation to integrate and propagate acoustic pressures generated by the propellers to observers in the far field at various RPM and distances for several propeller shapes. Overall, the aerodynamic efficiency of the non-conventional propellers did not sway from the conventional, straight propeller design. However, the dBA produced by each propeller requires further study, as the differences in sound pressure level between the designs could not be determined due to external environmental factors