Time-domain approach for acoustic scattering of rotorcraft noise

A new and efficient time-domain acoustic scattering method is applied to solve acoustic scattering of rotorcraft noise. The time-domain method provides a solution for all frequencies of interest in a single computation and is able to predict acoustic scattering of aperiodic signals. In the current method, the pressure boundary condition on the scattering surface is used to determine the strength of equivalent sources located within the scattering surface, which in turn are used to determine the scattered acoustic field. Linear shape functions are used to discretize the strength of the equivalent sources in time and singular value decomposition is used to find the least-squares solution and to overcome potential numerical instability. The prediction is found to be in excellent agreement with the exact solution. The numerical method is used to predict acoustic scattering of a Bo105 tail rotor noise by a representative fuselage. The time-domain code results of SPL are validated against the results obtained by a frequency domain analysis. Finally, acoustic scattering for an impulsive noise source is investigated to simulate main rotor BVI noise. A large computational time saving is achieved compared to the frequency-domain approach, in which the computation must be repeated for each frequency.