Numerical Simulation Study On The Ventilated Supercavitating Flow And Hydrodynamics Of Vehicle

The drag-reduction technology with ventilated supercavity can make the underwater vehicle brake through the traditional bottleneck and achieve travelling at high speed, which makes it have the significant military application value. The supercavitating flow is very complex due to its involving some hydrodynamic problems such as multiphase flow, turbulence, phase transition and compressibility. Quickly generating the best size and stable ventilated supercavity, deeply understanding the gas leakage way and the unique hydrodynamic characteristic of the vehicle are of the great significance for achieving the stable underwater trajectory of the vehicle. Around these issues, the basic modeling method and the detailed engineering problems have been carried out in this paper. The main works are as follows:Starting from the multiphase flow model, the homogeneous and inhomogeneous flow models are used separately to investigate the natural and ventilated cavitation, the predicting ability of the both models are evaluated by using the large number of experimental results and analysis of internal flow field. The results show that the inhomogeneous flow model has the high accuracy either on predicting the natural cavitation or ventilated cavitation and can give the more reasonable distribution of flow field, however, it has relatively large amount of computation. The homogeneous flow model can meet the project need on predicting natural cavitation.In the framework of homogeneous equilibrium flow, four cavitation models have been embedded into CFX using the secondary development and the cavitation model was selected by experimental data, the non-condensable gas term was considered in the cavitation model so that the influence of non-condensable gas to natural cavitation can be considered in the simulations of flow of three phases. The results show that the non-condensing gas can repress the natural cavitation when calculating the three-phase flow. The high speed natural cavitating flow and supersonic cavitating flow have been simulated by introducing the Tait state equation of water. The results show that under the supersonic flow condition the cavity has the obvious left-right asymmetry characteristic.A series of basic ventilated supercavitating issues have been investigated which include the scale effect of the diameter of water tunnel and viscous effect of the wall to ventilated supercavity, the results show that the choke effect of water tunnel can seriously result in the obvious deformation of the cavity. In addition, the developing process of ventilated supercavity, gas leakage way and the stability of supercavity were investigated using the steady and unsteady simulating ways, the result show that the ventilated supercavity has two main gas leakage way at the different stages. At the low-speed condition, the cavity has the self-excited oscillation phenomena, and the aft body of the vehicle can result in the large shedding of the cavity in the developing process of cavity and affects its stability.The steady and unsteady hydrodynamics of cavitator have been discussed in detail and the change law of planning force on the aft body of the vehicle is also studied by simulating the experiments in water tunnel. The results show that the cone angle can seriously affects the cavity shape and the hydrodynamics of the cone cavitator, the angular velocity basically does not affect the hydrodynamics in the deflection process of cavitator.Based on the relative motion principle, by adding the source term to the momentum equation, the uncontrolled trajectory of vehicle and the planning state presented by Savchenko as well as its influencing factors have been obtained by solving the motion equations and cavitating governing equations simultaneously. The results show that the centroid position seriously affects the uncontrolled trajectory of supercavitating vehicle.The numerical method on predicting the ventilated supercavity in this paper can be used to predict large number of supercavitating problems, and be the auxiliary tool of the experiments for ventilated supercavity.