Design and experimental investigation of perforated acoustic soft blade for counter-rotating propeller

The mechanism of contra-rotating propeller's aerodynamic noise is very complicated，and propeller-driven aircraft is not equipped passive noise reduction components such as nacelle liner to absorb noise during sound transmission，the noise generated by propeller will straightforward radiated to the fuselage and surrounding. Therefore，reducing the intensity of propeller noise is the key to the development of low-noise propeller aircraft. In this paper，a "soft blade" module is formed by placing a "small hole and through channel" structure on the suction front edge of spiral blade tip to balance the peak pressure at the leading edge of blade and reduce the load noise. According to the optimal parameters，the conventional propeller and the soft-blade propeller are manufactured，and the radiation noise measurement is carried out on the basis of the counter-rotating propeller aerodynamic noise test system. The results show that the counter-rotating propeller with perforated structure can effectively reduce the noise as well as ensuring the aerodynamic performance. At the 90° pointing angle，which has the most significant effect on the aircraft cabin，the noise reduction at the second-order passing frequency reaches 5 dB.