Investigations Of Flow-induced Sound And Flow Characteristics Over A Sphere Using Experimental And Numerical Methods

In modern times,it is very important for modern underwater vehicles to have a rather good acoustic performance, how to reduce their noise have become a key point for underwater equipment research. Flow-induced noise is one of the main sources of self-noise, its intensity increases rapidly with the rise of speed. Meanwhile, the effect of flow-induced noise can further highlight when effective control of mechanical and propeller noise are conducted. Therefore, it is of great value to study flow-induced noise for improving hydrodynamic noise capability of underwater vehicles.This article took balls as research object. Firstly, this paper conducted theoretical prediction and experimental measurements of the gravitational fall velocity of a ball, which provided the basis for the Reynolds numbers of balls and arrangement of hydrophones. Then, the experimental scheme of unpowered sinking experiment in a lake was introduced. Hydrophones was set at a depth where balls could achieve a uniform sinking state. In order to remove the infect of the environment noise, a wavelet threshold de-noising method based on CEEMD(Complete Ensemble Empirical Mode Decomposition) was proposed and applied to deal with the experimental data. Time domain signals of flow-induced sound reflected the ball passed monitoring points of hydrophones was obtained. Flow-induced sound signal after de-noising dispose was analyzed from time domain and frequency domain.The flow field around a sphere in uniform flow was calculated numerically by using LES(Large Eddy Simulation) method with a dynamic subgrid-scale model in subcritical and supercritical regime. The calculation results was compared with the experimental results, which proved the accuracy of the numerical calculation. Finally, the flow-induced sound was calculated based on the prediction results of flow field. The frequency spectrum and the sound directivity were also analyzed.The experimental scheme of unpowered sinking in the lake was designed and used to measure the flow-induced noise of balls. Mechanical noise was mostly avoided and decreased as well as the environment noise. The flow around the ball and the flow-induced sound was calculated numerically by using LES combined with FW-H equation. The work of this article can provide a new idea and new reference for the future experiments and numerical calculation of flow-induced sound.