Research For Design Of Lower Noise Exhaust Pipe Based On The Principle Of Throttling Depressurization

The underwater exhaust noise is one of the main ingredients of ship noise. We can saythat it has a great significance to control the underwater exhaust noise. In many cases, theengine exhaust pressure is much higher than the back pressure, so the main component of theexhaust noise is the exhaust jet noise formed from the high-pressure exhaust gas. It caneffectively reduce the exhaust noise that installs a pressure relief device in front of the exhaustexit to reduce the exhaust pressure. In this paper, the characteristics of underwater jet noiseare investigated by using theory, simulation and experimental method. The result providessome measurements in designing lower noise exhaust pipe.First of all, according to the jet noise theory, a kind of multistage orifice throttling deviceis designed, which is used to reduce the degree of turbulence near the exhaust vent. At thesame time, two different flow forms have been carried on the numerical simulation by meansof FLUENT to analyze the similarities and differences of two flow form. One flow form isexhaust to air environment and the other is exhaust to water environment. Then, the VOFmodel in FLUENT is employed to analysis the characteristics of the gas-liquid two-phaseflow in the orifice throttling device, in order to determine the main noise region of the flowfield. After that, the free jet noise and confined jet noise sound pressure level have beencalculated respectively by using the estimation formula. According to the simulation results,combined with the characteristics of the flow field and acoustic field, an optimized design ofsilencing structure has been proposed. Finally, a simulation experiment of engine underwaterexhaust is applied to detect hydrodynamic and acoustic performances of lower noise exhaustpipe, and it provides experimental support for the design of lower noise orifice structural.The results show that, one of the effective ways to reduce underwater high-pressure jetnoise is the installation of throttling device. A large abrupt pressure drop of exhaust isdispersed into a plurality of small pressure gradient by using series-connected several orificeplates. Through the comparison of the results, it has been proved that the multi-stage throttleplate can reduce the noise effectively and is the best choice.