The increasing demand for short-range passenger air transport and the strong push for aircraft with electric propulsion has renewed research interest in propellers. Despite the unmatched aerodynamic efficiency of propellers, their relatively high noise emissions limit widespread application on aircraft. Previous research has not systematically addressed the tradeoff between aerodynamic and aeroacoustic performance. This paper presents the results of an optimization study aimed at minimizing propeller noise without compromising aerodynamic efficiency. In the optimization, a blade-element-momentum-theory (BEMT) model is utilized which accounts for the effects of blade sweep on the blade loading. This BEMT model is coupled to a frequency-domain code for tonal noise prediction. A novel scaling approach is presented to directly relate the propeller noise emissions to the propeller thrust. Dedicated wind-tunnel experiments were performed to validate the analysis models. Good agreement between numerical and experimental results is obtained at low to moderate blade loading conditions. The optimization study shows that the blade sweep is an important design parameter to simultaneously maximize aerodynamic and acoustic performance. Compared to a modern baseline design, a noise reduction of 2.9 dB is achieved without reduction in propeller efficiency.

The unsteady aerodynamic characteristics of a 50° sweep delta wing performing pitching oscillations at angle of attack between 0° and 60° were tested in a water channel facility. Both force and velocity measurement results were analyzed and compared with the numerical simulation results for the pitching reduced frequency of 0.069 and 0.55. Both lift hysteresis and an unsteady phenomenon of leading-edge vortex (LEV) evolution were observed, which were significantly influenced by the pitch rate of the wing. As the wing pitch rate became sufficiently high, instead of being dissipated and convecting downstream, the LEV remained over the suction surface of the wing, which provide additional lift overshoot at a high angle of attack. In addition, as the wing pitched downstroke due to the negative induced camber effect, the lower surface of the wing turned from a pressure surface to a suction one and hence, there were significant lift losses.