Research On Vibration And Noise Radiation Mechanism And Control Of The Protrusion Induced By The Flow

The seawater gravity circulation cooling system uses the pressure generated by the vehicle on the seawater to press the seawater into the internal cooling system through the underwater protrusion structure,taking away the waste heat of internal facilities.The existence of protrusion structure reduces the water pump noise in the cooling system,but as the external structure of the vehicle,it destroys the fluid line shape on the surface of the vehicle and causes new hydrodynamic noise problems.At present,the research on underwater protrusion mostly focuses on the gravity flow characteristics and hydraulic performance,while the research on hydrodynamic noise caused by protrusion structure is less;Hydrodynamic noise is an important index of underwater vehicle,which is related to the safety ability of underwater vehicle.Aiming at the research on the structure of underwater protrusion,two basic protrusion models and supporting pipeline systems are established in this paper.By constructing the flow field calculation domain,the fluid flow state of the protrusion model under water is obtained.After theoretical analysis and numerical calculation,the generation mechanism of hydrodynamic noise of protrusion structure is explored,and the sound radiation characteristics of protrusion structure are discussed.Then,the influence of flow control technology of serrated leading edge and serrated trailing edge structure on the flow state of protrusion structure and the suppression of noise are studied.The influence of sawtooth leading edge structure and sawtooth trailing edge structure on hydrodynamic noise of protrusion structure is discussed,and the sawtooth parameters with the best noise reduction effect are explored.It is found that the existence of sawtooth leading edge and sawtooth trailing edge structure has an impact on the separation of the boundary layer on the surface of the protrusion structure,decomposes and breaks up the generation of large vortices in the flow field,suppresses the generation of horseshoe vortices,and effectively reduces the low-frequency noise in hydrodynamic noise.Finally,two typical protrusion models and protrusion models with sawtooth leading edge structure and sawtooth trailing edge structure are processed,and the supporting simple pipeline system is built to simulate the gravity circulation system in engineering practice,and the experimental measurement is completed in the gravity water tunnel in the underwater acoustic experimental building of Harbin Engineering University.The results show that the hydrodynamic noise of underwater protrusion structure mainly comes from the frequency band of 450 Hz and 800 Hz,and the vibration of underwater vehicle is mainly in the vertical direction.The sawtooth leading edge structure and sawtooth trailing edge structure have good noise reduction effect when the flow velocity is 4.62m/s and 7.72m/s.In the frequency band of 500Hz～ 2000 Hz,the noise reduction of the total level of radiated noise sound power is more than 1dB.