Research On Flow Induced Vibration And Acoustic Radiation Of Hydrofoil

Hydrodynamic noise severely damages the sound-stealth capability of the submarine. Propeller noise, and noise generating from appendages and control surface are typical hydrodynamic noise sources. Hydrofoil is the basic structure unit of the propeller, rudders and fins in submarine structure. So it is necessary to carry on the basic research on structure vibration and acoustic radiation of the hydrofoil. Research objects of this thesis are 2D and 3D hydrofoil. In this thesis, computational fluid dynamics(CFD) and the boundary element method(BEM) are used to simulate flow noise and second acoustic radiation. And the aim is to find the influences on the acoustic field from incidence and flow velocity.Lighthill’s acoustic analogy marks the taking off of research on flow noise. In recent years, BEM, combined with Lighthill’s theory, is applied to calculate the flow noise, and the approach develops rapidly. BEM is used to simulate the acoustic field of 2D and 3D hydrofoils in this thesis. Firstly, the flow field around hydrofoil is simulated by using Large Eddy Simulation(LES). After obtaining the pressure fluctuation from flow simulation, calculation of flow noise and second acoustic radiation is carried out, regarding the pressure fluctuation as dipole source and random exciting force respectively. At last, water tunnel experiments of vibration of 3D hydrofoil were performed, and the vibration properties are analyzed.There also put all the rules of flow noise and second acoustic radiation in different operating conditions into a summary. The influences on the acoustic field from incidence and flow velocity are investigated, and the results show that the sound pressure level around the hydrofoil increases regularly as the increasing of incidence and flow velocity in some frequency range. The comparison between pressure fluctuation and flow noise on surface of 3D hydrofoil is made. The results show that they have important internal relations and we can predict flow noise according the distribution of the pressure fluctuation. In addition, the relationship between flow noise and second acoustic radiation is discussed. We can find that second acoustic radiation depends mainly on natural characteristics of the structure. Last, the water tunnel experiments verify the accuracy of the numerical simulation.