Tonal and Broadband Noise Calculations for Aeroacoustic Optimization of a Pusher Propeller

A multidisciplinary analysis and optimization is carried out for a propeller in a real pusher aircraft configuration with the goal of reducing the radiated noise power levels, while preserving the aerodynamic efficiency. The optimization process involves the shape of the blade and the position of the engine exhaust ducts. A coupling of the unsteady aerodynamic and structural-dynamic blade models provides the aeroelastic propeller model that drives a tonal and broadband aeroacoustic prediction. The tonal noise results from the periodic flow unsteadiness due to the nonaxial flight and to the impingement of the engine exhausts on the propeller disk. The broadband noise is mainly due to the interaction between the blade leading edge and the exhaust turbulence. It is shown that the tonal noise overwhelms the broadband noise and that the optimization affects the shape of the blade at the tip and in the spanwise segment hit by the exhausts. An overall sound pressure level reduction of 3.5 dB is achieved at the takeoff condition, while preserving the design propeller thrust and resulting in a small penalty on the propeller efficiency in cruise.