With the help of empirical mode decomposition method this flow noise experiment was investigated in the towing tank. The key part of the EMD method is that with which and complicated data set can be decomposed into a finite and often small number of ‘intrinsic mode functions’. By the comparative method, the acoustic data have been collected with and without the cavity in all conditions respectively. After the proceeding of empirical mode decomposition, the intrinsic mode functions of the acoustic data have been gotten, and then do the PSD spectrum of each IMF. Compare the difference of each PSD spectrum between the result of with and without cavity, the flow noise which result from the cavity can be got. In this experiment, when the flow velocity is from 0.4m/s to 0.6m/s, the resonance phenomenon is observed. It appears the water in the cavity is up and down in the deep direction. This is so-called “Piston” phenomenon. The fluid fluctuating force in the cavity is a harmonic force. The frequency is the same with the resonance frequency and the value level is greater. When the flow velocity is more than 0.8m/s, there is no resonance phenomenon any more, under the help of EMD method, the fluctuating force which is consist of the shear layer oscillation and the water oscillation can be gotten.

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