Research On Flow-induced Vibration And Acoustic Radiation Of Underwater Vehicles

The flow-induced structural noise of underwater vehicles is chiefly caused by the structural vibration under the excitation of turbulent fluctuating pressure.The research and control of flow-induced structural noise can not only improve the acoustic stealth performance of underwater vehicles,but also effectively increase the detection threshold of sonar equipment,which is of great significance to the improvement of the comprehensive combat performance.Flow-induced structural noise belongs to a complex multi-physical field coupling problem,which involves the complex coupling relationship and energy transfer among flow,structure and sound.Its mechanism and characteristics are not only related to the speed and the line shape of the body,but also affected by the vibration characteristics under the fluid structure coupling.Due to the randomness and multi-scale of high Reynolds number flow,the study of flowinduced structural noise becomes more complex.From an applied perspective,this research investigates the vibration and acoustic radiation of underwater vehicles induced by turbulent fluctuating pressure.Firstly,based on the formation mechanism of turbulent boundary layer,the calculation method of fluctuating pressure of underwater vehicles based on the improved delayed detached eddy simulation is discussed.Then,the temporal and spatial distribution characteristics of fluctuating pressure of a submerged cone-cylinder-hemisphere combined shell are studied,and the wave-frequency spectrum characteristics in different regions of the shell are calculated.The relationship between fluctuating pressure and turbulent flow is analyzed.The numerical results indicate that the energy of turbulent fluctuating pressure is mainly concentrated in the lowfrequency regime,and wave-frequency spectrum can comprehensively reflect the temporal and spatial distribution characteristics of fluctuating pressure.Secondly,according to the radiated noise spectrum characteristics of underwater vehicles in different frequency regions,the flow-induced line spectrum noise in medium and low frequency is solved by vibro-acoustic FEM/AML method,while the band noise in high frequency is solved by SEA method.The spectrum characteristics and spatial distribution characteristics of flow-induced structural noise are discussed.It is found that the energy of flowinduced structural noise is mainly concentrated in the medium and low frequency range.And the line-spectrum characteristics of radiated noise are consistent with the inherent vibration characteristics of the structure.The peak frequencies of the radiated noise spectrum curve correspond to the coupled modes of the structure,and its near-field distribution is greatly affected by the structural vibration characteristics.Thirdly,based on the principle of reverberation method,full-frequency flow-induced structural noise of the submerged cone-cylinder-hemisphere combined shell is measured in a low-noise gravity water tunnel.The noise below and above the cut-off frequency of reverberation pool is measured by the combination of near-field direct measurement method and far-field spatial average method.Numerical results are compared with experimental data to validate efficiency and accuracy of the numerical method.It is found that overall sound power level of the flow-induced structural noise is approximately proportional to the 7th power of flow velocity.Finally,the full-frequency vibro-acoustic performance of the large-scale Suboff submarine induced by turbulent random fluctuating pressure is calculated through numerical methods.The fluctuating pressure distribution characteristics,the near-field and far-field acoustic field behavior,and spatial directivity are investigated systematically.Moreover,the influence of speed on the flow-induced structural noise of large-scale Suboff is studied.This research can provide support for the prediction,evaluation and control of transient acoustic radiation of underwater vehicles.