| This paper takes the supercavitation underwater vehicle as the research background.Aiming at the problem of the collapse of the cavitation interface under the action of the engine tail jet,the comprehensive application of experimental and numerical simulation methods is carried out to study the entrainment effect of the wake jet and its influence mechanism.Based on a small gravity water tunnel and a high-speed closed circulating water tunnel,experimental systems for the coupling of supersonic jets and cavitation are constructed.The compressible multiphase flow numerical calculation method for compressible multiphase flow is established through the VOF model coupled with the Level-set interface tracking algorithm.The formation and collapse mechanism of jet reflux cavitation is further studied.The study investigates the effects of the shape of the aeroform,the wake angle,the Froude number and the environmental pressure on the formation and stability of the bubble,so as to provide a technical basis for cavitation flow control of underwater vehicles.The experimental study on the coupling of ventilation cavitation and high-speed jet is carried out to explore the formation and collapse mechanism of jet reflux cavitation by controlling the ventilation and jet strength.The fine flow field structure of jet reflux cavitation is compared with that of head ventilation cavitation by numerical simulation.The results show that the initial supercavitation flow pattern is a necessary condition for the formation of jet reflux cavitation.With the increase of jet strength,the length of reflux cavitation decreases,and the cavitation tail gradually shrinks to the nozzle outlet.When the jet strength increases to the critical value,the supercavitation will undergo oscillation,rupture and collapse completely.The numerical results show that the jet induced recirculation zone between the nozzle outlet and the supercavitation closure point is the main factor to maintain the jet reflux effect,and the tail retracted droplets and their impact on the bubble interface under high jet strength are the main reasons for the collapse of the supercavitation interface.The effects of several parameters on the reflux supercavitation formed by the tail jet flow are analyzed.The effects of the dimensionless length coefficient,dimensionless diameter coefficient and tail jet angle on the reflux supercavitation are studied,and the cavitation collapse process of the large-diameter projectile model is analyzed.The results show that for the large-diameter projectile,the jet reflux cavitation breaks from the conical column section and separates to both sides,and then forms a tail cavitation at the back stage.The cavitation interface fluctuation and wall sticking effect caused by tail jet are the main reasons for its collapse.The angle of tail jet affects the critical jet coefficient of forming jet reflux cavitation.For the cavitation with great influence on buoyancy,the downward swing nozzle increases the critical collapse jet coefficient,which is conducive to the formation of reflux effect.The experimental research on the environment of different water depths is carried out to explore the influence of Froude number and environmental pressure for ventilation cavitation and jet reflux cavitation in the high-speed closed circulating water tunnel.The numerical simulation is carried out for large-scale supercavitation vehicle to reveal the mechanism of tail jet and cavitation with different strength.The results show that the increase of Froude number and ambient pressure is conducive to increase the cavitation size and improve the cavitation stability.Under the action of low-intensity jet,large-scale supercavitation vehicle has significant backflow inflation effect.However,under the action of supersonic jet,it is difficult to achieve effective jet reflux effect.The main reason is that the interface fluctuation of cavitation caused by jet and its propagation to the downstream.The increase of wave amplitude leads to the cavitation interface sticking to the wall,and the reflux inflation channel is cut off.The results of this paper can provide an effective method for cavitation flow control and provide strong support for the development of supercavitation vehicle technology. |
