Study On Expansion Characteristics Of Supercritical Carbon Dioxide Gas Gun

The gas gun has been widely used in laboratory high-speed collision test,artificial rainfall and other fields because of the advantages of simple structure,stable pressure,high safety and wide adaptability.Carbon dioxide has been widely used in the field of gas blasting because it could rapidly expand into supercritical state under the condition of low critical pressure and critical temperature.At present,due to the low expansion efficiency of the gas medium(air,hydrogen and other gases)of the gas gun,the pressure in the barrel is low and the gas compression device is complex.In this study,the first-class gas gun and supercritical carbon dioxide,the gas medium,are combined.The characteristics of doing work of expansion are simulated and analyzed,which causes that the characteristic curve of doing work of expansion and the law of influencing factors are obtained.The compact and high-speed gas gun could be widely used in the factory and dangerous area.Based on the thermodynamic model of supercritical gas,field model of flow and motion model of projectile,the mathematical model of doing work of expansion of supercritical carbon dioxide gas gun is established,and the characteristics of doing work of expansion of gas gun are analyzed.The effects of three single factors,i.e.initial pressure,projectile mass and barrel diameter,and three two factors,i.e.initial pressure and barrel length,initial pressure and barrel diameter,initial pressure and projectile mass,are compared with the expansion performance of gas gun.On this basis,based on the mathematical model of doing work of expansion,the influence of three factors on the gas gun is analyzed by the orthogonal experiment,and the influence degree of each factor is obtained.In this study,the numerical simulation model of supercritical carbon dioxide gas gun is built and simplified,and the rationality and accuracy of the simulation conditions are verified.In order to explore the characteristics of doing work of expansion,the characteristics of gas gun are analyzed based on inlet mass flow,projectile force and projectile velocity,which are doing work of expansion indexes.On the basis of the above simulation analysis,the four factors of initial pressure,projectile mass,barrel length and barrel diameter are s calculated,and the three doing work of expansion indexes and flow field characteristics with the four factors’ condition are compared.The simulation model of out of barrel is built and simplified in this study.The simulation model is divided into three parts basing on the actual boundary conditions.In order to explore the change of the doing work of expansion outside the gas gun,the carbon dioxide’s pressure and velocity at the special points in each part are recorded and analyzed.Through comparing the three doing work of expansion indexes(inlet mass flow,projectile force and projectile velocity)and cloud picture(velocity,pressure and temperature),the characteristics of doing work of expansion out of the gas gun are analyzed.Based on the above simulation analysis,two factors of initial pressure and projectile quality are simulated and analyzed,and the characteristics of three expansion indexes with the two factors’ condition are compared.The experimental test platform of supercritical carbon dioxide gas gun is built in this study,and four PMM high-pressure sensors and high-speed camera are used to record the changes of pressure in the barrel and flow field outside the barrel.The accuracy of the mathematical model of doing work of expansion is verified by comparing the experimental and numerical results of pressure and projectile velocity in the gas gun.