Flow noise and its suppression in exposed hydrophone

Abstract Underwater acoustic communications (UWAC) is an important technology in deep-sea research. In UWAC system, when the hydrophone as an acoustic receiver is exposed under sea and moves along with its attached objects, its performance will be affected by various ambient noises, among which its generated flow noise is the major source. This would influence the performance and shorten the communication distance of UWAC system. In this paper, we try to unveil how the flow field is correlated with the hydrophone flow noise. The large eddy simulation (LES) method and acoustic analogy are applied to simulate the flow field and the sound field around hydrophone, respectively. The hydrophone flow noise at different moving velocities with different attack angles is obtained. The flow noise result of experiments launched in an anechoic tank agree well with the flow noise simulation results, and both show that as the hydrophone moves faster, its sound pressure level climbs up higher. To suppress the flow noise, two kinds of cage to be installed on hydrophone are proposed, i.e. a cylinder cage and a serrated trailing edge cage. The simulation results show that the serrated trailing edge cage outperforms the cylinder cage. This study provides theoretical basis for improving the signal-to-noise ratio of low-frequency UWAC system.