Sound scattered by helicopter fuselages in descent flight conditions

The aim of this paper is the analysis of the influence of the fuselage on the noise field emitted by a helicopter during a descent flight, when it mainly acts as a scatterer for the acoustic disturbance radiated by the main rotor in BVI conditions. In particular, the sound scattered by the fuselage is evaluated through a non-conventional acoustic boundary integral formulation based on the FfowcsWilliams and Hawkings equation, that requires the knowledge of the only incident pressure over the surface of the scatterer. This approach avoids the computationally expensive interactional aerodynamic analysis of a multibody configuration, in that the isolated main rotor solution is the only aerodynamic input to be determined. A boundary element method is applied to solve numerically the integral formulation for the scattering, and the resulting prediction tool is applied to evaluate the noise radiated by a realistic main-rotor/fuselage configuration.