Numerical Study On The Buffering Characteristics Of Low-speed Water Entry For The Head-jetting Vehicle

With the rapid development of anti submarine technology,the role of cross medium vehicles in combat systems is becoming increasingly significant.During its cross medium water entry process,the sudden change in the density of the navigation medium at the moment of entry will cause it to be subjected to significant impact loads,affecting its working performance.Therefore,the study of inflow buffering is crucial in the development of cross medium vehicles.As a proven and feasible buffering method,active jet unloading of the vehicle has good application prospects.Therefore,in this paper,the multiphase flow characteristics and mechanical characteristics of the head jetting vehicle in the low-speed water entry process are numerically studied,and the impact load changes in the water entry process and the buffering performance of the head jetting are analyzed.Firstly,a numerical simulation was conducted on the water entry process of the projectile with or without jet,and the rationality of the calculation model was verified by comparing it with the results of literature.On this basis,the flow field distribution and impact load changes during water entry were compared between the two cases of the aircraft’s head jet and non head jet,and the buffering effect of the head jet during the vehicle’s water entry process was analyzed;Secondly,the effects of water entry speed and angle on the force and buffering effect of the vehicle were calculated;Finally,the effects of initial jet height(starting from40 mm,60mm,80 mm,and 100 mm above the water surface),number of jet ports(1,2,and 4),and jet port structure(equal diameter,contraction,and expansion)on the force and buffering effect of the vehicle during water entry were investigated.The calculation results show that when there is no head jet structure,the maximum overload and surface pressure peak of the navigation body increase with the increase of water inlet velocity and decrease with the decrease of water inlet angle;When the head jet vehicle enters the water,an increase in the entry speed and a decrease in the entry angle of the vehicle will lead to a decrease in buffering performance;Increasing the initial jet height is more conducive to the development of ventilated cavitating and can improve the buffering performance of the head jet;The ventilation cavitating of a single jet port wrap the head of the vehicle more completely,and the buffering effect of the head jet is better;The use of relatively small diameter equal diameter jet ports is more conducive to the development of axial size of ventilation cavitating,and the high-pressure zone is further away from the head,resulting in better buffering effect.