Research Of Noise Mechanisms Of Submarine Sail Model

Submarin sail is part of the bridge and the most important projecting attached part of submarine. Projecting attached part induces non-uniform of flow field. From the monitoring of submarine noise it can be known that the hydrodynamic noise from the submarine sail is one of the main noise sources. The scaled down model is taken as the studing object in this thesis. The machanics, charicteristics of noise of the submarine sail have been analyzed. Then, the low-noise design technology and noise assesing method have been concluded. Four parts forms the paper. Firstly, the calculating of the characteristic of flow field out of sail has been done on the basis of CFD. The result shows that the time-averaged physical quantity of sail flow field is non-uniform. The mechanisms and characteristics of noise source, transition flow, turbulent flow, boundary-layer separation, wake flow have been simulated. Then, the conclusion that the space gradient of physical quantity of flow field in the transition range is bigger than that in other areas can be concluded. Accordingly, the transition range was the most important position where the noise sources are located. Furtherly, the relations between the trasition point's time-averaged press and turbulent zone's time-averaged press with the velocity of the flow was deduced. And this conclusion also offers theoretical support to constitute the relations between submarine velocity and the radiated noise level of sail. Secondly, the structural characters of sail has analyzed on the basis of FEM by use of ANSYS software, i.e. the mode of sail. Besides, the structual vibration characters of sail excited by forces on different positons of near the trasition point have been discussed and the main vibration modes of sail have also been obtained. Thirdly, the corresponding radiated sound power and sound field have been calculated by BEM. In terms of the comparations of acoustic physical quantity when the exciting forces are located at different positons, the main principal of flow field control can be induced. Lastly, after sumarizing the analyses above, the main characters of noise sources of sail have been obtained. Furtherly, the main principal and method of low-noise control of sail have been induced, which will provide the reference to the optimum design of acoustic stealth of submarine sail.