Flow Effects on Measurement of the Modal Decomposition of Acoustic Field in a Hard Wall Cylindrical Duct

A method of determining azimuthal and transverse wave modal decomposition in a hard wall cylindrical duct by a double Fourier-Lommel’s transform of acoustic pressure in a cross section is experimented in a flow facility. It is shown that this method is suitable for flows with non uniform mean profile. But it is found that it is very sensitive to random noise which results from flow instabilities.