Development Of Compressible Cavitation Flow Solver Based On OpenFOAM And Cavitation Analysis Around The Deep-Submerged Body

The quest for speed and efficiency in the field of marine and offshore engineering is endless,and bodies moving at high speed in the water usually produce cavitation phenomena.As the cavitation number decreases,the cavitation pattern will gradually change from sheet cavitation to cloud cavitation and super cavitation with a larger degree of cavitation,during which the growth process,shedding process and collapse process of the cavity are involved,causing turbulent eddy motion,pressure wave release from cavity collapse,cavitation instability,flow separation and other highly unsteady fluid mechanics problems.The previous studies primarily used incompressible cavitation models for numerical simulations,which cannot simulate the propagation of pressure waves released during the cavitation collapse,and the propagation of pressure waves can further affect the motion state of the cavitation and even produce spalling on the navigation body structure.In this paper,a compressible two-phase flow cavitation model with mass transport is developed and numerical simulations are mainly used to study the cavitation evolution around the hydrofoil and projectile,etc.By analyzing the cavitation evolution and the mechanical mechanism behind the cavitation instability of the navigable body in water,we focus on the propagation of the pressure wave released from the collapse of the cavitation after taking into account the compressibility of the fluid,which can provide reference for the research of cavitation and cavitation instability in engineering fields such as underwater weaponry and underwater machinery,and the main research contents of the thesis are as follows:In this study,a two-phase compressible cavitation flow solver is implemented in the open source software OpenFOAM,which ignores the thermal effects between water and vapor during the cavitation evolution.The barotropic fluid hypothesis to close the system of NavierStokes equations.The solver uses the finite volume method(FVM)to discretize the equations,capturing the water/vapor interface through the volume fraction of the water and vapor phases,and,like the official OpenFOAM solver,can directly invoke the applicable cavitation model,turbulence model,etc.,which has good applicability.The numerical simulation of cavitation flow is conducted by choosing the experimental conditions of typical hydrofoil and projectile structures in the considerable published literatures.The numerical simulation results agree well with the experimental results,in order to verify the validity of the established numerical model,the effects of different mesh resolutions,different turbulence models,and different cavitation models on the starting position of the cavity,the overall cavitation evolution,and the pressure coefficient distribution on the surface of the structure are discussed.Based on the verification of the computational method,the mechanical mechanism behind cloud cavitation instability,the most complex of all cavitation phenomena,is discussed from the perspectives of two-dimensional hydrofoil cavitation and three-dimensional projectile cavitation.Compared to the traditional method of solving incompressible cavitation flow,the pressure wave propagation induced by the collapsed cavity is also well predicted,taking into account the compressibility of the fluid,and not only can we reproduce the re-entrant jet effect well.In this paper,we focus on the differences between the two mechanisms,provide a detailed summary of the role of the re-entrant jet,discuss the effects of pressure wave propagation at different locations and stages of cavitation development,and study the pressure pulsation characteristics to the surface of the structure caused by the shedding cavity collapse processes.On this basis,this paper studies the characteristics of the cavity patterns of several conventional torpedo head types under different cavitation numbers,and compares the effects of different head types and different cavitation numbers on the cavitation patterns respectively.In the paper,a comparative study of the pressure distribution on the surface of the navigable body under the action of cavitation is conducted,and the process of cavitation pattern transformation and the mechanical mechanism behind it are discussed and analyzed,which can provide basic technical support for the design of conventional head type of torpedo to a certain extent.