Extensions of the orthogonal beamforming to identify multiple multipole sources
* Presenting author
Some aeroacoustic sources are analogous to multipole sources, such as dipoles or quadrupoles. For these sources, the conventional beamforming methods may yield questionable source locations and strengths due to the monopole assumption. With the aim to identify sources with various directivities, a normalized-and-square beamforming combined with an inversed method is proposed. Multiple sources are separated by the eigendecomposition of the cross-spectral matrix of array signals. The influence of source directivities can be eliminated by modifying the eigenvectors. After the sources are located, the source strengths can be estimated by an inverse method using the spherical harmonic expansions. The proposed procedure is verified by numerical simulations of various multipole sources and an experiment of an Aeolian-tone dipole combined with a loudspeaker. It shows the potential to identify the airfoil noise or the airframe noise with complex directivities.