Study On The Expansion Of Conical Distributed Multiple Gas Jets In A Cylindrical Liquid Chamber

At present,two launching methods are used in underwater small caliber weapon.One is launching directly in water and another is using a seal baffle to separate water.These two methods have a rapidly rising bore pressure and a complicated drainage device respectively.In this paper,a new method of underwater firing is presented that uses combustion gas to drain away water.In this new method,with several small holes arranged at the front of the bullet,part of combustion gas which behind the bullet is lead to the launch tube to develop gas curtain for drainage.The launch environment changes from liquid to gas,which provides a possible way to avoid the shortage in current methods.In order to understand the mechanism of this method,it is necessary to study the characteristics of the interaction between the gas jets and liquid in a cylindrical chamber during a firing process.Under this background,experimental and numerical studies of the interaction between the conical distributed multiple round gas jets and liquid are carried out to understand its mechanism.The main research content and results are list as follows:(1)Experimental studies on the expansion of conical distributed multiple gas jets in a cylindrical liquid chamberAn experimental platform is designed and established to study the interaction between multiple gas jets and liquid.With a high speed camera system recording the evolution of multiple Taylor cavities in a cylindrical liquid chamber,the expansion of gas jets and gas-liquid turbulent mixing are analyzed under different injection pressures and nozzle structure parameters(such as the orifice size,the injection direction and orifice number).Results show that Taylor cavities are separate and expanding along the orifice axes in the initial stage of expansion.In the expanding along the wall stage,lateral gas jets expand along the wall and converge.With an increasing injection pressure or a smaller angle between central and lateral orifice axes,the expanding velocity of each gas jets decreases more rapidly.With more lateral orifices,expanding velocities of central and lateral Taylor cavities decreases slower.(2)The numerical model and numerical studies on the expansion of multiple gas jets in a cylindrical liquid chamberAccording to the experiment observation,a three dimensional unsteady numerical model of this two phase flow is established.Evolution of multiple Taylor cavities and back flow zone under a typical condition are analyzed with a numerical simulation.Distribution of gas and flow parameters(such as pressure,velocity,temperature)in the cylindrical space is discussed.Results show that several Taylor cavities are developed after combustion gas injected into liquid.The central not lateral Taylor cavity has a necking-break.The expansion of combustion gas jets in cylindrical chamber can be divided to four zones which are near-nozzle transition zone,stable extending zone,fast expanding zone and liquid-only zone.In stable extending zone,the gas volume fraction changes a little along the axis.In the near-nozzle transition zone and fast expanding zone,the gas volume fraction changes rapidly with the change of section position.In Taylor cavity,the under-expanded gas has 2-3 expansion-compression process in the gas core zone near the nozzle.The gas pressure,velocity and temperature along the central Taylor cavity axis have irregular waves due to the complex gas-liquid interface which exists near the nozzle.These parameters have a regular distribution along the lateral Taylor cavity axis.(3)Numerical studies on the influence of nozzle structure on the expansion of multiple gas jets in a cylindrical liquid chamberWith numerical simulations of different structure nozzles,the influences on evolution of multiple gas jets are analyzed.Results shows that with an increasing central orifice size,The central Taylor cavity expends faster on both axial and radial directions and squeeze the lateral Taylor cavity.In gas core zone,the shock wave structure in central Taylor cavity grows with an increasing central orifice size,the dimensionless pressure,Ma and temperature curves are similar.With an increasing central and lateral orifice diameter,the necking of central Taylor cavity weakens.The decreasing and increasing rate of dimensionless pressure curve in gas core zone keep the same,but the dimensionless pressure increases earlier and reaches a higher level.With a bigger angle between central and lateral orifice axes,the convergence of central and lateral Taylor cavities is harder.With more lateral orifices,the necking-break of central Taylor cavity appears earlier.The dimensionless curves of central Taylor cavity change irregularly.(4)Numerical studies on the influence of injection pressure on the expansion of multiple gas jets in a cylindrical liquid chamberThe influence of injection pressure on the expending of multiple gas jets is studied.The expansion features of multiple gas jets under the coupling action of injection pressure and nozzle structure are also analyzed.Results shows that the Taylor cavities expand more quickly with a higher injection pressure;same is the evolution of back-flow zones in Taylor cavity.The average pressures on radial sections increase linearly with an increase of injection pressure.The research on the coupling action of injection pressure and injection direction shows that the angle between central and lateral orifice axes controls the evolution of back-flow zone;the increasing injection pressure accelerates the evolution.Under different injection pressure,the nozzle with a bigger angle between central and lateral orifice axes improves the gas distribution in the fast expanding zone.The research on the coupling action of injection pressure and lateral orifice number shows that the nozzle under a lower injection pressure and a bigger lateral orifice number is easier to develop a detached bubble from central Taylor cavity.To avoid this situation,a possible way is to increase injection pressure or decrease lateral orifice number.The multiple gas jets drainage is a new launching method of underwater gun.The unclear mechanism of interaction between gas jets and liquid impedes its application in engineering.In this paper,the experimental and numerical studies on the interaction of multiple gas jets and liquid are carried out.Some positive results have been obtained,which provides the foundation for the further development of the new launching method.