Aeroacoustic and Aerodynamic Characteristics of Propeller Tip Geometries

A series of experiments were conducted in an aeroacoustic wind tunnel facility to investigate the aerodynamic performance and noise characteristics of propellers with various modifications to its tip geometry. A baseline propeller was designed for static hover conditions. The blade was adapted with the intention to reduce, divert or eliminate the blade tip vortex which is responsible for blade vortex interaction noise. All of the propellers were fabricated using advanced additive manufacturing techniques and tested experimentally in both static hover and forward flight modes of operation. The blade thrust and torque, as well as the radiated far-field noise were collected over a range of rotational speeds in static hover and forward flight conditions. Data was also collected at a thrust-matched condition for each tip modification permitting comparison of figure of merit at static hover. Particular attention was given to the 1st blade passing frequency tone and its directivity and magnitude. Various treatments show promise in changing the directivity and reducing the magnitude of this tone. Each of the categories of tip modification; anhedral, swept and tapered show potential in reducing the overall sound pressure levels as well as the blade passing frequency tone while providing the same thrust output as the unmodified blade. Numerical simulations using the SU2 solver were performed on selected tip modifications to provide further insights into the effects of changing the propeller tip geometry while in forward flight conditions. The numerical simulation results correlate well with the experimental data.