Research On Gas Gaseous Jet Flow Structure And Thrust Characteristics Of Solid Rocket Motor Working In Deep Water

Solid rocket motors(SRM)utilized in propulsion systems of underwater vehicles are of advantages such as simple structures,rapid responses and fast combat readiness.Due to the unique features of deep water environment,high density and high pressure,gas jets induced by SRM exhibit intense heat and mass transfer phenomena,resulting in considerably different performance characteristics in comparison with those working in air.Therefore,studies exploring the mechanism of underwater SRM have great significance and value to the high-speed underwater vehicle design.According to the actual SRM tests,for purpose of making numerical simulations of underwater SRM,high Reynolds k-? turbulence closure model is used to solve N-S equations,and the multi-phase VOF model which is established to track the interface of gas and water easily is also employed to describe the mixing process.In the present paper,gas jets induced by SRM considering gravity-buoyance and phase transitions are explored.Furthermore,motion models of the rocket-propelled underwater vehicles are addressed.The thrust oscillation which occurring in SRM was simulated numerically in the paper.Based on results in the study,it has been found that the working conditions have great influence on the thrust oscillation of underwater SRM.Simulation results refer to working conditions of over-expansion and under-expansion in axisymmetric models are compared.It has been concluded that oscillation frequency of over-expanded gas jets shows multiple order and with peak frequency.Analysis of the first four order frequencies identifies that bulging and back-attack are of relevance.However,in gas jets working in under-expansion conditions,there are no neck-breaking and back-attack phenomena,instead of a "quasi-back-attack" phenomenon,and in the position of bulging resonance appear in the same period.Results of three-dimensional model of the jets considering gravity and buoyancy indicate that gravity and buoyance will change the shape of gas jets,and jets considering gravity and buoyance is more consistent with the experimental results.In horizontal jets,the structure change because of torque reversal effect in gravity and buoyance.While vertical jets show a loop of open bubble,which will lead to the instability of thrust.After analyzing reasons of the generation and broken of this loop bubble,it has been found that loop bubble is the interaction of relative motion of gas and wall,as well the viscous force of the gas.Observation of a long-time vertical gas jet shows that the steady jet gradually turns unsteady under the influence of various factors,resulting in unbalanced gas wake.In order to analyze the interaction of underwater hot gas jet and water,phase transitions which are suitable for complex underwater environment are established.By modifying the source terms of the governing equations,numerical simulation to achieve heat transfer and mass transfer between the gas,vapor and water is explored.And comparison of the typical axisymmetric flow field structure and thrust under the effect of phase transitions has concluded that the phase transition will reduce amplitude of thrust oscillation and frequency.In horizontal jets,it is found that the phase transitions increase the roundness of the jets bubble.Numerical simulation results in this paper are sufficiently consistent with the experimental results when the SRM start to work.The unidirectional motion model of a rocket-propelled vehicle,a water tunnel model and a six-degree freedom motion model are established.By comparing the curve of total force-time of vehicles and typical flow field,it has been found that incoming flow will reduce the oscillation amplitude of the vehicle,and increase the vibration frequency.In addition,the amplitude of force oscillation shows sudden change point.By contrast to the static gas jet,conclusion are obtained that the static gas jets are mainly effected by shockwave effect,while the dynamic gas jets are primarily compressed by boundary layer,and the amplitude of oscillation is less than that static.By comparing different flow velocity,it is found that when the incoming flow is faster,the oscillation frequency is higher and the amplitude of oscillation is smaller.Numerical simulation models are established in the paper,and the conclusions are as follows: As the forms of shockwaves are different under different working conditions of SRM,gas jets in highly under-expanded conditions depict a "quasi-back-attack" phenomenon.When considering the effect of gravity and buoyancy,the horizontal jets will show torque reversal effect,while vertical jets will generate a loop bubble,which will all result in the instability of motor.For the reason that there's a complex process of heat and mass transfer in actual gas jets,a phase transitions model is established.Results are found that phase transitions will reduce the amplitude and frequency of thrust.As the booster motor is moving with the vehicle,the incoming flow will be coupled with the jets.The wakes of jets is compressed by the flow boundary layer so that the oscillation amplitude of vehicle decreases,and the frequency increases.Conclusions and results in this paper will lay the foundation for further research of underwater SRM.