Numerical and experimental study on spectrum and temporal coherence analyses of flow noise caused by sinusoidal vertical motion of sonobuoy

Flow noise caused by sinusoidal vertical motion of the sonobuoy reduces the signal-to-noise ratio (SNR) of the recorded signal. Therefore, understanding the physical properties of the flow noise is important for improving the working performance of the sonobuoy. The present work is dedicated to investigate the characteristics of the flow noise of sonobuoy generated from vertical motion based on the combination of numerical calculations and experimental results. The flow noise of the hydrophone under time varying stream velocity is predicted using a hybrid computational fluid dynamics (CFD)-Ffowcs Williams-Hawkings (FW–H) equation technique. The flow noise calculated with the hybrid computational method is in good agreement with that analyzed by the experimental measurement and empirical formula. The numerical calculation results of the flow noise under time-varying stream velocity condition reveal that the spectrum and temporal coherence of the flow noise exhibit the periodic changes same as that of the stream velocity. These analyses and conclusions are verified by experimental data. The study in this paper will contribute to signal processing of the sonobuoy and thus improving SNR of the measure signal.