Studies On The Interaction Characteristics Of Multiple Wall Combustion-gas Jets With Liquid Medium

In response to the practical problem of high chamber pressure and low muzzle velocity in launching process of the underwater gun,this paper proposes a new technology for highly efficient launching,that is,guiding parts of propellant gases in combustor to discharge in front of the projectile can drain off water existing before the projectile at the same time with the movement of the projectile.Based on the above background,the experimental research and numerical analysis are developed to study the interaction characteristics of multiple wall combustion-gas jets with liquid medium in cylindrical filling liquid chamber,and the influences of nozzle area,nozzle shape,nozzle number and injection pressure on the distribution of characteristic parameters in flow field are emphatically discussed.Furthermore,we would try to reveal the drainage mechanism of multiple wall combustion-gas jets.The main research contents and results are as follows:(1)Comparative analysis on expansion characteristics of round combustion-gas jet and rectangular combustion-gas jetAn unsteady mathematical and physical model for combustion-gas jets expanding in liquid is established to respectively simulate the expansion process of single round combustion-gas jet and rectangular combustion-gas jet in the cylindrical filling liquid chamber,and the temporal and spatial distribution laws of two-phase components,static pressure,static temperature and velocity and the evolution rules of vortices are illustrated in detail.Results show that,under the same injection pressure and nozzle area,the head displacement of the rectangular jet is always less than that of the round jet in the whole expansion process.For the rectangular jet the highly localized corner would induce corner instability and thus enhancing gas-liquid turbulent mixing which would weaken the axial turbulent kinetic energy.Meanwhile,the rectangular combustion-gas jet still satisfies the mechanism of axis switching when expanding in confined liquid space.(2)The experimental research on the expansion processes of multiple wall combustion-gas jets in cylindrical filling liquid chamberAn experimental platform on the expanding of multiple wall combustion-gas jets in cylindrical filling liquid chamber is designed and set up,while the evolutionary processes of multiple Taylor cavities are recorded by means of high-speed digital photographic system and multi-angle observation results can be obtained by reasonably designing the experimental optical path.In the research,we focus on the influences of nozzle area,nozzle shape,injection pressure and nozzle number on the expansion characteristics of multiple wall combustion-gas jets in liquid medium.Results show that,when multiple wall combustion-gas jets expand in cylindrical filling liquid chamber,the axial expansion velocity of jet is higher than the radial expansion velocity,the wall jets get close to each other and achieve convergence eventually,and the heads of the Taylor cavities separate from the filling liquid chamber wall and offset to the middle of the chamber with time going on due to intense interference effect between jets.Meanwhile,the bigger the nozzle area,the more the inlet turbulent kinetic energy causing the smaller the jets gap at later stage of the expansion process.Accompanied by nozzle shape changing from rectangular to semi-circular,the axial expansion of jet becomes more rapid but the gas-liquid turbulent mixing intensity becomes weak.As the injection pressure increases,the kinetic energy of jet increases and the multiple wall jets reach to the top of the chamber earlier.Under the same injection pressure and total combustion gases condition,the more the nozzle number,the less the inlet turbulent kinetic energy of each of multiple wall jets and the slower the average axial expansion velocity of Taylor cavities.(3)The three-dimensional unsteady mathematic and physical model in gas-liquid two-phase flow field and analyses on the typical experimental conditionBased on the theory of multiphase fluid mechanics,we develop a three-dimensional unsteady mathematic and physical model to simulate the expansion process of the four wall combustion-gas jets in liquid on the typical experimental condition,and the detailed distributions of characteristic parameters in jet field are acquired.Results show that,expansion waves and compression waves are formed in nozzle near field as the static pressure at the nozzle exit is much higher than that of the ambient liquid.When the combustion-gas jets pass through the expansion waves and compression waves,the pressure,temperature and velocity fluctuate intensely.Moreover,the non-dimensional profiles of streamwise velocity near wall region present temporal and spatial self-similar property in axial plane between two opposite wall jets,but only present temporal self-similar property in axial plane between two adjacent wall jets.(4)Numerical analyses on the influences of injection parameters variation on the expansion characteristics of the four wall combustion-gas jetsBased on the experimental research,numerical analyses on the influences of multi-parameter variation on the expansion characteristics of four wall combustion-gas jets are carried out from the different point of the nozzle area,nozzle shape and injection pressure.Results show that,under the same injection pressure,the larger the nozzle area,the bigger the jet momentum,which leads to bigger volume of the Taylor cavity in the cylindrical chamber and results in better drainage effect on the whole water in the chamber.As the nozzle shape changes from semi-circular to rectangular,the highly localized corner would induce corner instability enhancing the gas-liquid turbulent mixing that leads to rapid dissipation of jet energy and results in faster decrease of temperature and velocity along axial and radial direction.With the increase of aspect ratio of the rectangular nozzle,the corner instability would be enhanced,which leads to stronger radial turbulent kinetic energy and results in better drainage effect for the nozzle near field.When the injection pressure increases,the inlet turbulent kinetic energy of jet enhances that leads to faster expansion velocity along axial and radial direction,and results in bigger volume of Taylor cavity in cylindrical filling liquid chamber thus getting better drainage effect on water in the gun barrel.(5)Numerical studies on the interaction characteristics of multiple wall combustion-gas jets with liquid mediumBased on the experimental research and numerical analysis of the four wall combustion-gas jets,numerical studies on the interaction characteristics of multiple wall combustion-gas jets with liquid medium are developed further,focusing on the coupling effect of multiple Taylor cavities and influences of nozzle number,nozzle area and nozzle shape on the distribution of characteristic parameters in jet filed.Results show that,under the same injection pressure and total combustion gases,the inlet turbulent kinetic energy of each jet in the case of six and eight wall jets is less than that in the case of four wall jets,which leads to smaller Taylor cavity and stronger blocking effect of liquid medium on nozzle near field,so the complete expansion waves and compression waves structure can not be formed in nozzle near field at the initial expansion stage,and the formation time lags behind that in the case of four wall jets.Moreover,through analysis we know that the intensity of the turbulent mixing and convergence effect is mainly decided by the coupling effect of inlet turbulent kinetic energy of each jet and interference effect between jets,so the turbulent mixing effect is extremely intense and the convergence effect is more obvious in the case of six wall jets when compared with other two cases of four and eight wall jets,which leads to better drainage effect for the case of six wall jets.