Experimental Investigation and Numerical Modeling of Noise Generated by Installed Pusher Propellers

In this paper, noise emissions from two pusher propellers installed on a wing are investigated both experimentally and numerically. Aerodynamic and aeroacoustic measurements were carried out in the acoustically treated open test section of the Pininfarina Wind Tunnel and encompassed extensive parametric analyses in terms of geometrical configurations and flight conditions. Significant noise reduction is achieved by installing the propeller at the wingtip (up to 3 dB), as well as increasing its distance from the wing (up to 2 dB). The experimental results provided the identification of optimal configurations in terms of noise impact and originated a database used to validate and assess a numerical model. The numerical approach is based on a lattice Boltzmann method combined with a Ffowcs Williams-Hawkings analogy providing predictions of noise installation effects. Numerical simulations comprised different wing-propeller configurations and flight conditions, reproducing test cases explored in the wind-tunnel test campaign. Comparisons with experimental results are given, with focus on tonal noise and directivity. It is shown that the numerical method is able to reasonably predict the noise installation effects with maximum deviations of 4 dB and reproduce its sensitivity to the variation of relevant flight parameters.