Numerical Simulation On The Influence Of Ventilation Parameter On Supercavity Shape

Two physical processes in water flow will produce low density cavities composed of the vapor or the gas.One is the vaporization caused by the highspeed flow when the local pressure falls below a saturation value.The other is the ventilation by injecting noncondensable gas.When a supercavitating flow occurs.It results in the multiphase flow of gas,vapor and water in the near-wall region of underwater vehicle except its head which touches with water only.The ventilated supercavitating flow relates to the complex flow phenomenon andmechanism,such as multiphase flow,turbulence,mass transfer,compressibility and unsteadiness.In this thesis,some key problems about ventilated cavitating flow,including the cavity morphology,flow structure,non-axisymmetry and reducing drag mechanism,were investigated using the theoretical analysis,mechanical test and numerical simulation.The thesis begins with the Rayleigh-Plesset equation which describes cavity,gain a rational mass transport relationship between water and vapor.The finite volume method was employed to solve the Navier-Stokes equations and the k-εequations.In the thesis,using the double equation model together with the natural cavitation module of FLUENT 6.2,simulated out two phases vapor cavity flow containing vapor and water,and the simulation result consisted well with classic experimental data.At the same time,based on the average Navier-Stokes Reynolds equation,using finite volume method and separation algorithm,a simulation of steady two-phase gas-liquid ventilation cavity flow was performed in the framework of mixture two-phase flow model pattern.Pressure coefficient distribution shows that the ventilation cavity simulation in the role of natural cavitation should be considered during the ventilation process in the tunnel under the calculating condition.Combining the two cavitation simulation results above,the paper established multiphase flow model which was used to simulate the complex ventilation cavity flow field. Based on the Mixture multi-phase model ands the calculated results of teady-state natural cavity,this thesis carried through a transient ventilated cavity numerical research,achieving multiphase ventilated cavity flow simulation including gas, vapor and liquid.By comparing with the experimental data and theoretical value, testify the validity of the model and calculation accuracy,The results showed that the cavity size became larger with the increase of ventilation quantity,after forming the supercavity,cavity size changed little when continue to increase ventilation quantity.The current domestic study on natural vapor cavity flow is mainly based on numerical simulation,ventilated cavity investigation is achieved through the tunnel test,in the published literature has not yet found relative simulation of ventilated cavity flow according to actual trial process.Finally investigated the effect of gas ventilation temperature on the cavity shape and dimension,results showed that with the increase of ventilation temperature,the cavity radius and length become larger.