Prediction of turbulent flow noise inside an acoustic sounder cavity

The detection performances of an underwater acoustic system are strongly dependent from the self noise level on the receiving array (for example the array of an echo sounder system placed in a cavity located in the keel). In most cases, turbulent flow noise along the hull is the dominant component in the self noise. Then, it is important to quantify it at the design stage. In this paper, three theoretical models are presented. The first one uses a decomposition of the excitation in the frequency/wavenumber domain, and assumes that the plate representing the acoustic window is infinite. The others use for the excitation a pressure fluctuation spectrum and correlation distances obtained from experiments. The vibro-acoustic response of the plate and of the fluid cavity uses a « statistical energy analysis » approach for the second model, and a finite element representation for the last one. First, the numerical models are compared to an experiment carried out in a water tunnel facility. The best results are obtained with the finite element model, but if three dimensional geometry is taken into account, large computational effort is required. The statistical energy analysis model gives fair results at medium/high frequencies, however with a slight over-estimate. The noise levels predicted by the infinite plate model are too low, indicating that this model is not adapted to the problem under consideration. A prediction of self noise in a cavity housing the array of an echo sounder system is then computed, an compared to ambient sea state noise levels.