Spatial transformation of the discrete sound field from a propeller
A technique for the spatial transformation of the discrete sound field from a propeller is proposed that is based on solving the Ffowcs Williams and Hawkings equation with quadrupole source term neglected. Since the blade surface velocity is fully specified, numerical inversion of Farassat's integral is used to relate the blade surface pressures to the finite number of measurements in the acoustic field. With the reconstructed aerodynamic loading, the whole sound field is naturally predicted using Farassat's integral. Since the inverse problem is ill posed, the Tikhonov regularization method is used to stabilize the solution. The optimal regularization parameter is chosen by generalized cross-validation criterion. Numerical results show that the reconstruction is inaccurate in the presence of measurement noise (error) but the spatial transformation of discrete sound filed remains satisfactory.