Study On Generation Mechanism And Propagation Characteristics Of Flow Noise Of Underwater Blunt Body

In recent years,more and more attentions have been paid to the noise of underwater vehicles.The research on the flow noise of underwater blunt body is of great significance.In order to study the flow noise of underwater blunt body,some methods of computational aeroacoustics are introduced and improved to meet the needs of hydrodynamic acoustics.In this paper,the linear Euler equation applicable to the water medium is used to calculate the sound field,and the wavenumber optimization immersion boundary method is proposed to deal with the acoustic reflection problem of the surface of objects with different shapes.In this paper,the flow-acoustic splitting technique and acoustic boundary condition method are used to complete the coupling of flow field and sound field.In order to improve the calculation accuracy of the flow-acoustic splitting technique and to reduce the dissipation and dispersion,the second derivative scheme of wavenumber optimization is derived.In view of the different meshes between flow field and sound field,and the non-uniform mesh of flow field,the existing high-precision interpolation method has been improved,and a high-precision difference scheme was deduced according to the same principle.In this paper,some models with theoretical solutions are used to verify the validity of these theoretical and numerical methods.In order to test the research method and self-developed software used in this paper,the flow noises of underwater two-dimensional flow around a square cylinder at low Reynolds number and a cylinder at high Reynolds number are calculated.This paper uses CFD(Computational Fluid Dynamics)software using large eddy simulation method to calculate the flow field,and through the self-programmed software to complete the flow-acoustic separation and sound field calculation,at the same time,using the sound analogy method for calculation and comparison.The correlation between the flow noise and the wake vortex shedding is proved,and the interaction between the wake vortex and the blunt body is the main source of the flow noise.In this paper,the three-dimensional calculation of the flow noise around an underwater sphere at high Reynolds number is carried out.The flow field is calculated by using the large eddy simulation method of commercial CFD software,and then the flow-acoustic separation and sound field calculation are completed by the self-programmed program.At the same time,the traditional acoustic analogy method is used to calculate the acoustic directivity.The results are compared with the experimental data,which verifies the effectiveness and practicability of the research method and the self-developed software used in this paper.It is also found that the acoustical directional deflection of the flow around the sphere is highly correlated with the deflection of the wake vortex,and there is a long period variation with it.