Study On Interior Ballistics And Multiphase Flow Characteristics During The Low Resistance Launching Process Of An Underwater Gun

At present,the launching methods of underwater guns mainly include the fully submerged launch and the sealed launch,but both of them have great limitations.The fully submerged launch,of which the barrel is filled with water,the high resistance will cause extremely high maximum chamber pressure during the shooting process.In order to ensure the launching safety,the charge must be reduced,so the obtained initial velocity of the projectile is low and the damage power is insufficient.The underwater sealed launch is equipped with a muzzle water sealing device with complicated structure,therefore,it is difficult to adapt to the complicated and variable underwater continuously.shooting environment.Based on this,a new method of high-efficiency and low-resistance underwater launching is proposed in this paper---gas-curtain launch of underwater gun.The launching method can utilize the existing smoothbore gun to realize the low-resistance,high-speed launch without additional complicated muzzle water sealing device.It is realized by optimizing the design of the projectile and the charge,and guiding partial gas behind the projectile in real time to exclude the water column in the barrel.In response to this new method,experimental and theoretical studies on the interior ballistics and gas-liquid interaction characteristics of underwater gas-curtain launch are carried out.The main research contents and results are as follows:(1)A visual shooting experiment system is designed and built for underwater gun.Firstly,the interior ballistics performance experiments of air launch,underwater fully submerged launch and sealed launch are carried out.On this basis,two gas-curtain projectiles are designed(Including the central nozzle and the side wall nozzle),and the comparative experiment of the interior ballistics characteristics of the multi-condition gas-curtain launch are carried out.The experimental results show that under the same maximum chamber pressure,the initial velocity of the gas-curtain launch is higher than the fully submerged launch.And,under the equial initial velocity,the maximum chamber pressure of the gas-curtain launch is lower than the fully submerged launch.Therefore,the effectiveness and advancement of this new launch method are experimentally verified.The interior ballistics performance of the sealed launch is similar to the air launch.(2)Based on the experiment,the interior ballistics and multi-dimensional multiphase flow models of underwater gas-curtain launch are established,and numerical simulation is carried out for typical experimental condition.Both the temporal spatial distribution characteristics of gas-curtain evolution,turbulent intensity,pressure,velocity,temperature in the gas-liquid two-phase flow field and the interior ballistics parameters are obtained.Then,the mutual coupling law of four typical stages of gas-curtain evolution in the barrel is analyzed,and the drag reduction mechanism of gas-curtain launch is revealed.That is,before the projectile starts,the gas jet is ejected from the projectile head to form a gas-curtain,which discharges the water column in the barrel in real time.Then the projectile moves in the low-pressure gas-curtain to achieve low-resistance and high-speed launch of the underwater gun.(3)By changing the loading and structural parameters,the characteristics of the multi-phase flow field in the barrel and the interior ballistics of the underwater gas-curtain launch are numerically analyzed.The calculation results show that,for the central nozzle(?=3mm)gas-curtain projectile,under certain charge,there is an optimal venting mass flow rate of 81.5g/s when the mean ventilation mass flow rate is increased from 74.3g/s to 87.9g/s.As the water depth increases from 1m to 100 m,which is equivalent to an increase in the external environmental pressure around the muzzle,the ventilation mass flow rate should be increased as appropriate,otherwise the interior ballistics performance will decrease.At 100 m depth,the ventilation mass flow rate needs to be increased to about 88.0g/s.Under the same conditions of the charge and the projectile mass,increasing the diameter of the central nozzle,not only the projectile head pressure is reduced,but also the initial velocity and propulsion efficiency.Under the same conditions of charge,projectile mass and nozzle area,the gas-curtain projectile with four side wall nozzles can acquire higher initial velocity and propulsion efficiency than the projectile with central nozzle(?=4mm).This fully demonstrates that the injection mode and structural parameters are one of the key factors determining the interior ballistics performance of the gas-curtain launch.Based on the above work,the advantages of gas-curtain launch compared to fully submerged launch are further analyzed under high chamber pressure.Under the conditions of the same projectile mass,the equial charge and maximum chamber pressure,the maximum chamber pressure and the initial velocity of the gas-curtain launch are 353.2 MPa and 775.1 m/s,respectively.However,the maximum chamber pressure and the initial velocity of the fully submerged launch are 383.3MPa and 582.8 m/s,respectively.This further theoretically demonstrates that compared with the conventional fully submerged launch,the newly proposed gas-curtain launch can control the chamber pressure,improve the muzzle velocity,and obtain the interior ballistics performance close to the air launch.(4)The interior ballistics and muzzle multi-phase flow theoretical model of underwater gun sealed launch is established.Based on Fluent software,the muzzle flow field characteristics under variable parameters are numerically simulated.The calculation results show that the Mach disk structure is formed when the projectile exits muzzle for 70?s due to the joint effect of the gas-liquid interface and the projectile bottom.While the gun is launched in the air,only affected by the projectile bottom,the Mach disk is still not formed when the projectile exits muzzle for 200?s.In the underwater sealed launch,the free expansion zone is much smaller than the air launch.The variation of the parameters in the upstream flow field of the Mach disk is similar to that in the air,but the parameters in the downstream of the Mach disk are fluctuating,and the distribution characteristics are more complex than those in the air.Under the different loading conditions,the axial maximum displacement of the Taylor cavity of the sealed launch increases linearly with time.