Numerical Simulation On Flow Noise And Flow-excited Noise Of Submarine Under Fluid Structure Interaction

The hydrodynamic noise of a submarine sailing underwater is caused by velocityfluctuation in turbulence boundary layer, fluctuating pressure on solid boundaries andstructural vibration due to fluid structure interaction. The velocity fluctuation inturbulence and fluctuating pressure on solid boundaries are acoustic quadruples anddipoles respectively, which comprise of flow noise. The structural vibration due to fluidstructure interaction results in flow-excited noise, which increases the value of noise.Hydrodynamic noise severely damages the sound-stealth capability of a submarine.Therefore, it is of primary importance to study the generation and characteristics ofhydrodynamic noise.Lighthill’s acoustic analogy marks the beginning of research on flow noise.Traditional acoustic analogy is based on the assumption of compact acoustic source,under which it can get an accurate result for acoustic information in the far-field, but itcould lead into mistakes when dealing with the near-field acoustics. As an alternativemethod in solving acoustic problems, Boundary Element Method is able to accuratelypredict acoustic information in all field, due to its special handling of the singularitypoint.This paper takes the SUBOFF submarine as research model. Firstly, by using LargeEddy Simulation, the flow field around submarine is calculated. The numerical solution iscompared with experimental data, which validates the numerical simulation. Then byusing traditional acoustic analogy FW-H equation and BEM, the flow noise at certainfeature points along X, Y, Z direction is calculated. Comparison between the resultsacquired by these two methods show that in far-field the results are quite similar, but innear-field the result by FW-H is higher.Secondly, this paper studies the flow-excited noise of submarine under flowstructure interaction, which is the superposition of flow noise and flow-excited vibration noise. By applying the fluctuating pressure acquired in flow field calculation as anexternal force to submarine structures, the vibration displacement of submarine structurecan be obtained. Then using the Helmholtz equation, flow-excited vibration noise isobtained. Numerical simulation results show that flow-excited noise is higher than flownoise under the same frequency. In near-field, the difference between these two values isquite large. But as the distance to submarine boundary increases, flow-excited noisedecreases more rapidly than flow noise, which makes the difference between these twovalues gradually smaller. Finally, the difference is almost constant.Thirdly, this paper has studied the changing patterns of flow-excited noise at variousfeature points under different flow field velocities and submarine thicknesses. The resultsshow that the increase of flow field velocity will increase flow-excited noise, and theflow-excited noise curves under different velocities reach their maximum values atalmost the same frequencies. The increase of submarine thickness will decreaseflow-excited noise, and the flow-excited noise curves under different submarinethicknesses reach their maximum values at different frequencies.