Spectral-boundary-integral compact-source formulation for aero-hydroacoustics of rotors

This paper presents an aeroacoustic compact-source formulation for predicting tonal noise generated aerodynamically by rotors that is applicable to hydroacoustic problems as well. Based on the knowledge of blade sectional loads, it is suitable for reducing the amount of aerodynamic data required (particularly relevant, for instance, in maneuvering motion) and is applicable also when detailed blade pressure is not available. The Kössner- Schwarz airfoil aerodynamics theory is applied to derive the chordwise pressure jump equivalent to the sectional loads provided (either by measurements or computational tools).Azeroth-order boundary element method is applied for spanwise integration of the resulting compact-source, spectral-integral formulation. Numerical investigations concern a helicopter main rotor in descent flight and a marine propeller in nonuniforminflow. They demonstrate that, increasing the number of spectral coefficients (and corresponding sectional loads), this compact-source formulation converges toward solutions providing accurate noise predictions, even for rotors with irregular blade pressure distributions.