Numerical simulation of underwater flow noise from open cavity under different attack angles

摘要

An underwater open cavity, such as a submarine's open weapons firing tube, is a typical kind of structure that can induce fluid noise. To study the fluid noise generated by the submarine's open tube, greater attention is paid when the cavity's opening is vertical to the flow direction. This paper focuses on flow noise induced by an underwater cavity having openings under small attack angles, and simulations were conducted for different small attack angles. The Large Eddy Simulation method combined with Lighthill's acoustic analogy theory is used by software FLUENT and ACTRAN to simulate the underwater flow noise. The submarine cavity model is simplified as a cylinder with a hemisphere on one end, and there are openings on the top of the hemisphere. The flow field and the underwater fluid noise from this model have been numerically simulated for three cases. Case 1: the cavity has no opening; case 2: the cavity has four openings; case 3: the cavity has six openings. The inflow direction is assumed to be in parallel with the cylinder and against the hemisphere, and the flow speed is assumed to be 5 m/s and 10 m/s in all cases. First, the open cavity transition zone is calculated and analyzed by use of FLUENT. Then, the flow noise frequency characteristics and its far field pattern are calculated and analyzed for different flow velocities by use of ACTRAN. The numerical results show that the frequency spectrum curve of those cases with different flow speeds are very similar. However, the flow noise level will get higher with the increase of the flow speed and number of openings. The far field will tend to have obvious space directivity for the cases with more openings or at higher flow velocity, and the main lobes of the far field pattern coincided with the openings' direction. Finally, the radiated sound power level from the cavities was compared and analyzed for three different attack angles. Simulations show that the flow noise will get higher with the increase of the attack angle in the case of small attack angles. So, the opening of the model should be closed completely, or the flow velocity and attack angle should be lower, in order to decrease the fluid noise level.