An Analytical–Numerical Aerodynamic Formulation for Efficient Aeroacoustics Analysis of Rotorcraft

This paper presents an analytical-numerical aerodynamic/aeroacoustic formulation for the analysis of the tonal noise emitted by helicopter rotors and propellers. It is particularly suited for those configurations dominated by local high-frequency changes (both in time and space) of blades inflow velocity. The solution of the Ffowcs Williams-Hawkings equation for noise radiation prediction is combined with the frequency-domain Küssner-Schwarz formulation that yields the sectional, unsteady aerodynamic loads, starting from the knowledge of the downwash on the airfoil due to blade motion and inflow induced on it by any external source of perturbation. Here, the blade inflow is assumed to be evaluated through a 3D, unsteady, panel method formulation suited for the analysis of rotors operating in a complex aerodynamic environment. This aerodynamic/aeroacoustic model gives a computationally efficient solution procedure that may be conveniently applied in preliminary design/multidisciplinary optimization applications. The proposed approach is validated through comparison with the (accurate, but computationally expensive) acoustic field obtained through the blade pressure loads directly evaluated by the time-marching panel-method solver. The results are provided in terms of blade loads, noise signatures and sound pressure level contours.