An Investigation Of Ventilated Cavitating Flow Of A High Speed Underwater Vehicle

Underwater launched missile is an important military equipment, which has the characteristics of concealment and flexibility, it is inevitable to produce natural cavity while the ambient pressure varies and missile accelerates. The natural cavity has an adverse effect upon flow load, structural vibration and noise. Ventilated cavity technique is adopted to obtain stable cavity to eliminate the adverse effects of natural cavity. Although there're some researches on cavity upon the surface of the sub-launched missile, the understanding is still inadequate in temperature effect and scale effect in respect to projectile body's ventilated cavity. This paper therefore carries out its theoretical analysis and numerical simulation on this part. The unsteady cavitating flow in a longitudinal gravity force field was studied by using numerical simulation method during vertical launch submarine missile rising.The primary results and innovations are given as follows:1. The complex physical process of vertical motion of vertical launch submarine missile is simplified as a axisymmetrical problem ,by CFD software FLUENT12 and secondary development platform, based on the Navier-Stokes equations and Mixture multiphase flow model, coupled natural cavitation model, established the multiphase flow model of gas, vapor and water.2. The dynamic mesh is adopted for the vertical movement of launching missile led to the changing of computational domain. Also, the dependence of the grids, the difference schemes, cavity models and the effect of turbulence models, were analyzed and compared. 3. The formation of ventilated cavity during vertical launching missile (including the stage of supplementary gas) can be divided into three stages. In the initial stage, only a small amount of gas covers small area after the nozzle, the initial cavity has little effect on flow field and hydrostatic pressure distribution shows obviously at the periphery of the missile ;The second stage , the cavity grows rapidly, length of which increased to nearly 1 / 4 L, obvious natural cavitation does not be observed because of high environmental pressure;In the stage of supplementary gas, the ventilated mass flow rate becomes twice of the previous two stages and cavity length becomes one half of the previous two stages. Clouds of water and vapor mixture can be observed at the end of the high speed underwater vehicle.4. In ventilated cavity formation process, the projectile surface pressure coefficient decreases with the decreasing of ambient pressure, and increases along the cylinder after the closed region. The peak of recovery pressure begins increasing for the adverse pressure gradient increases and then decreases for the effect of environmental pressure reduction.5. By meeting the conditions of geometric similarity model, same Fr number and cavitation number, the length of the cavity has a certain degree of decrease with the model scale decreases. Integral the mass flux of these 5 cases, indicates that the simulation results are smaller than the analytical value.6. In high temperature conditions, the thickness of water and vapor mixture significantly increases at the end of the cavitation zone. In 300K, the lowest temperature of gas appears at the vent hose nozzle; In 500K-2000K, it appears in the top of the nozzle along the velocity direction about 5 times of the diameter of the nozzle area. As the ventilation temperature increases, the main body cavity pressure coefficient increases gradually with increasing temperature, but the cavity length increases because of the influence of high temperature gas.By virtue of numerous calculation and analysis carried out in the present work, the knowledge of complex ventilated cavitating flows with gas, vapor and water multiphase are deepened, important data is accumulated , the understanding of related mechanism has been enhanced ,and it will be worthy for further studies.