Study On The Gas-liquid Interaction During The Gas Episodic Launching Process Of An Underwater Gun

The sealed launcher and the submerged launcher are the two most commonly used traditional underwater gun launcher,but there are some limitations in the two methods.In the sealed launcher,the sealing system is relatively complex,and the submerged launcher has a lower muzzle velocity.The gas episodic missile launcher is a new launching technology,which restricts the resistance and improves the muzzle velocity.To make up for deficiencies of the tradition al underwater guns,the submerged gas episodic gun launcher is proposed,on the base of submerged gun launcher and gas episodic launcher.At present,the research in submerged gas episodic gun launcher is still in a stage of exploration,lacking of the understanding on the gas-liquid interaction during the launching process,as well as the interaction between the projection and the gas curtain.Based on the background of submerged gas episodic gun launcher,the experimental research and numerical analysis are conducted to study the generation process of the gas curtain with multi combustion gas jets.The main research contents and results are as follow:(1)At first,an experimental platform is set up to simulate the injection of the multi combustion gas jet,the sprayer adopts an injection structure with 1 central nozzel,4 oblique nozzles and 4 side wall nozzles.On this base,the experiment is carried out,and the generation process of the gas curtain in the liquid filled tube is observed.The results demonstrate that the center jet and the oblique jets are injected simultaneously,and expansion along the nozzle direction.Then the side wall jets come out and expand along the chamber wall.With the axial expansion of the side wall jets,they merge with the oblique jets and form the side jets.Then the side jets are further mixed with the center jet and the gas curtain is finally generated,which promotes the liquid medium to move in the tube.As a result,the synergistic drainage effect of multiple gas jets is realized.With the same size of nozzles,the greater the injection pressure,the faster the gas curtain expands,and the stronger instability the gas curtain has at the top.Under the same injection pressure,the drainage performance of the multiple combustion gas jets is weakened when the center nozzle is increased.However,with increased oblique nozzles,the drainage performance of the multiple combustion gas jets is improved.(2)A simulator for the interaction between the multiple combustion gas jets and the liquid under motion of the projectile is designed,and the generation characteristics of the gas curtain in the liquid-filled tube during the moving process of the projectile is observed.The results show that the expansion sequence of the multi combustion gas jet during the moving process is consistent with the static condition of the projectile.During the experiment,with promotion of the combustion gas,the velocity of the projectile is gradually increased,and finally reached a steady value.With the same sprayer structure,the greater the injection pressure is.the better drainage performance the gas curtain has,and the greater velocity the projectile tube reaches.With the same injection pressure,increase the center nozzle,the drainage performance of the gas curtain is not improved and the moving velocity of the proj ectile remains the same.Increase the oblique nozzles,the drainage performance of the gas curtain is improved,and the moving velocity of the proj ectile is raised.(3)On the base of the experiment.,a three dimensional numerical model is established to simulate the interaction between the multi combustion gas jets and the liquid medium.Numerical analysis is conducted with a typical condition,and the distribution of component,pressure,velocity and temperature in the flow field is acquired.Numerical results show that,at the beginning,the center jet and the oblique jets are injected at the same time,then the side wall jets come out.At this stage,the multi combustion gas jets expand along the nozzle independently,and the combustion gas expands sharply after injected from the nozzles.Therefore,the velocity of the combustion gas increases,the pressure and the temperature decreases along expansion direction.As the front top of the gas jets is blocked by the liquid,the velocity of combustion gas drops and the pressure rises that forms a high pressure area on the top of the gas jets.With the expansion of multi gas jets,the side wall jets converge with the oblique jets to generate the side jets,which expands along the chamber wall.After that,the side jets merge with the center jet,that forms the air curtain in the tube.During the merging process,turbulent mixing occurs between the multi combustion gas jets,that induces the pressure to rise in the gas curtain.Under the same sprayer structure,with the increased injection pressure,the interaction between the combustion gas and liquid is enhanced that the pressure and temperature are both raised in the flow field,and the velocity of the liquid medium is also increased.Under the same conditions of injection pressure and nozzle number,increasing the center nozzle,the axial expansion performance of the center jet is improved,and the inhibition on the side jets is strengthened.And the mixing between the multi jets is enhanced that the pressure and the temperature rise in the gas curtain.While the collaborative drainage performance of the multi gas jets is not improved.Under the same conditions of injection pressure and nozzle number,with the enlarged oblique nozzles,the inhibition on the side wall jets is strengthened.The axial expansion capability of the side jets is firstly weakened and then strengthened,but the axial expansion capability of the center jet is firstly strengthened and then weakened.Meanwhile,mixing between the multi gas jets is enhanced in the gas curtain that pressure and temperature rises in the mixing zone,and the collaborative drainage performance of the multi gas jets is improved.Under the same conditions of injection pressure and nozzle size,increasing the number of nozzles,the axial expansion of the side jets is restricted,but the circumferential expansion is easy to converge that the collaborative drainage performance of the multi gas jets is improved.(4)On the base of the simulated launching experiment,numerical simulation on the interaction between the multi combustion gas jet and liquid during the moving process of the projectile is conducted,and evolution characteristic of the flow field is obtained.Numerical results indicated that the interaction between the moving projectile and the gas curtain accelerates the axial extension of the gas curtain and improves the drainage performance of gas curtain.With the pushing of the projectile,the gas curtain is compressed that the axial size of the gas curtain is decreased,and the pressure is increased.With the same nozzle size,increasing the injection pressure improves the drainage performance of the gas curtain.As the moving velocity of the projectile is also increased that enhances the interaction between the projectile and the gas curtain.As a result,the gas curtain is further compressed,and the pressure rises in the gas curtain.Under the same injection pressure and projectile velocity,increasing the center nozzle enlarges the center jet,but the side jets are restricted.With an enhanced center jet,the interaction between the multi jets is strengthened that the pressure and the temperature rise in the flow field.Nevertheless,the collaborative drainage performance of the multi gas jets is decreased.Under the same injection pressure and projectile velocity,increasing the oblique nozzle enhances the inhibition on the side wall jets.The axial expansion of the side jets,generated by the oblique jets and side wall jets,shows an upward trend,but the expansion performance of the center jet is firstly enhanced and then weakened.With increase of the slant nozzles,the drainage performance of the gas curtain is improved.(5)Coupling internal ballistic model with interaction model between the multi gas jets and liquid,the submerged gas episodic launcher is established.Through the numerical simulation,the generation characteristics of the gas curtain and motion characteristics of the projectile are obtained.Numerical results show that the multi gas jets converge in the gun barrel and form a gas curtain.During the generation of the gas curtain,the pressure in the flow field declines,that forms a low pressure gas channel in the path of the projectile.Compared with the traditional submerged gun launcher,the gas episodic launcher can improve the moving velocity of the projectile and restrain the pressure in the chamber.The internal ballistic performance of the gas episodic launcher varies with the change of launch conditions.Increasing the loading density,the rising rate of pressure is increasing at the beginning,but the muzzle velocity changes in non monotonic way.With an increased combustion rate of the coated gunpowder inner layer,the pressure and the muzzle velocity are both increased during the launching process.Increasing the thickness of the gunpowder,the pressure drops during the launching process,the muzzle velocity also changes in non monotonic way With an enlarged extracting force,the chamber pressure rises,and the muzzle velocity is also increased.The greater the launching depth is,the greater the environmental pressure reaches.Thus,the axial expansion of the gas curtain is restrained.As a result,the pressure rises in the chamber,and the muzzle velocity is decreased.