Research On Multiphase Flow Field And Dynamic Characteristics Of Underwater Thermal Launch Of Missile

Due to compact configuration, simple structure, short-range missile and other characteristics, underwater thermal vertical launching mode gradually becomes an important trend in the development of submarine-launched tactical weapons. Underwater thermal launch, associated with the complicated flow of high velocity gas in tube and air-water multiphase mixture flow in tube opening, show complex flow state and change rules, which has a vital influence on launch power, launch load and so no. In addition, in the underwater environment, back pressure changes caused by launching depth, flow generated by ocean current and craft speed, high temperature gas in cylinder opening and heat and mass transfer process produced through air water mixing may impact underwater thermal launching process. Researches on flow state and change rules during underwater thermal launch, and analysis of formation principles and influence factors of launch power and launch load have great theoretical significance and engineering value in the understanding of the phenomena and laws during underwater thermal launch and in the development of the domestic underwater thermal launch technology. The underwater thermal launch process of submarine missile which is concentric canister structure is focused on in the paper. Based on numerical calculation, theoretical analysis and experimental method, the multiphase complex flow state and formation principles, launch power and launch load during launching are studied. To achieve them, the main work includes the following aspects.Firstly, high-speed gas flow in the tube, air-water multiphase mixture flow and variations of the computational domain caused by the movement of missile during underwater thermal launch were analyzed, and the numerical model which met the process of underwater thermal launch was established. For the numerical model, 3-dimensional unsteady N ?S equation was used to describe the basic state of fluid motion, and the calculating equation was built with RANS, and also the RNG?k ?? turbulence model which was based on the assumption of eddy viscosity was applied to do closed treatment on the RANS equation. MIXTURE model was used to simulate the process of two or multiphase flows in the numerical model. Phase transition model based on the saturated steam conditions was utilized to simulate air-water two-phase heat and mass transfer process. Considering the missile movement during launching, dynamic mesh was used to simulate grid update caused by the domain changes.Secondly, based on underwater thermal launching process in depth of 30 m, underwater thermal launch process was studied and analyzed using concentric canister structure, identifying the typical characteristics, such as the development change rule of bubble in tube opening, gas flow state in tube, launch power and of launch load. The results indicated during underwater launch exhausts from the inner and outer tube gap of concentric canister interacted with water, forming jet bubble near the tube, and effected by phase interaction process, the viscous force of missile surface and Coanda effect of gas flow, shape of jet bubble experienced three typical forms and significant bubbles breaking and shedding didn’t appear, moreover pressure inside the bubbles oscillated near the environmental back pressure. Impacted by pressure losses and the jammed effects of exhausts caused by the gap friction flow, pressure in the tube was higher than the pressure of bubbles and environment in tube opening. Then addition force contributing to the missile’s motion was generated. In the research, the addition force accounted for a maximum of 93% of launch power. In the launch process, the gas jet exhausted from engine formed significant impact pressure in the bottom of concentric canister, and the higher pressure in tube generated larger vertical. Therefore, higher requirements of stiffness and strength of launch tube were proposed. In addition, the pressure load of missile was also significantly higher than the load of deck environment.Thirdly, typical factors of underwater thermal launch, such as launch depth, heat and mass transfer between phases, craft speed or ocean current conditions, the launch tube structure, were analyzed, to specify the principles of these factors on launch power and launch load. The results showed the increase of launch depth contributed to the increase of the pressure of the head and bottom of missile, but the pressure of the bottom of missile had a smaller increase than the head pressure, so the addition force decreased and then the velocity of missile decreased; the heat and mass transfer process influenced launch process by decreasing the gas temperature near the tube opening, increasing the gas flow exhausted from the tube slightly, and pressure in the tube reduced, and also the addition force slightly reduced but had little effect; water flow caused by craft speed or ocean current influenced launch process by changing the position and shape of bubbles in tube opening, and in the low speed of flow the gas flow in the bubbles root in tube opening had less effect, and the effect of flow on missile motion during launching was also very small; the gas flow exhausted from the tube was directly affected by the gap size of launch device, influencing the launch process, load in the tube significantly, and the gap size was smaller, the gas flow exhausted from the tube decreased, launch power and launch load increased correspondingly.Fourthly, typical flow process, the dynamic features and the factors of underwater thermal launch were analyzed comprehensively, and the theoretical calculation model of concentric canister in underwater thermal launch process was established. The theoretical calculation model was built by partition modeling on inner and outer flow fields of concentric canister launcher(CCL). For the inner flow fields, the mass balance equation, state equation and energy equation were built considering the gas quality changes, status changes and energy changes. For the outer flow fields, the jet bubble change development model was established using Rayleigh-Plesset equation, energy equation of jet within bubble and energy equation of jet flowing into the bubble, and the missile motion was simplified as a model which moved only along the axis. By comparing the theoretical calculation results with CFD, the analyzing results indicated theoretical calculation model can reflect the typical gas state and load characteristics of underwater thermal launch of concentric canister, which can serve as convenient means for theoretical research, program design and the selection of parameters.