Flow noise response of a diaphragm based fibre laser hydrophone array

Flow noise is one of the factors limiting the performance of towed array systems, especially thin-line arrays. Response of a fibre laser hydrophone array to axisymmetric boundary layer wall pressure excitation is presented. A simplified theoretical model is obtained to predict the flow noise levels inside fluid filled towed arrays. An axisymmetric wall pressure model was used along with frequency-wavenumber transfer characteristics obtained from finite element analysis (FEA) to arrive at flow noise estimates under normal operating speeds. The results were then compared with internal pressure spectra obtained from the simplified theoretical model. The flow noise levels corresponding to operating tow speeds below 2 m/s for the analysed configuration are found to be lower than the nominal low-level ambient noise floor observed in the sea for frequencies greater than 200 Hz. The results show that the flow noise isolation achieved through fluid filled array construction reduces with increase in tow speed.