Aeroacoustic characterization of two pusher propellers in different configurations

In this research, the effect of rotor to rotor interactions has been experimentally investigated. Pusher propeller configurations have been considered because of the several benefits offered over the traditional arrangements in the fields of civil aviation. For instance, the aircraft wing is no longer exposed to the swirling and turbulent slipstream and the position of the propellers considerably reduces the noise impact on the fuselage, yielding the potential of a low cabin noise level. However, in general, the exterior noise of pusher propellers is augmented by the interaction with impinging wakes and exhaust jets. To this purpose, an experimental study has been performed on different Unmanned Aerial Vehicles (UAVs) propellers considering that advances in inexpensive control systems and electronic devices have greatly promoted the development of UAV in a wide range of applications. The rotors investigated change in number of blades, pitch angles and loading conditions. The aim of the work is to investigate the noise field generated by the propellers in pusher configuration performing the measurements both for single rotor and considering the interaction between two co-rotating propellers having the same geometry to highlight the effect of the relative position on the noise produced. Three hub separation distances have been considered in order to find the optimized configuration in terms of acoustic impact. Tests have been performed in the Roma TRE semi-anechoic chamber of the Laboratory of Fluid Dynamics "G. Guj" on five UAV propeller models using three microphones properly positioned to cope with the supposed potential sound sources.