Research On The Superposition Effect Of Hydraulic Water Hammer Under The Action Of Double Fragments

Hydrodynamic Ram(HRAM)is a dynamic phenomenon occurs when a fragment impacts a liquid-filled tank at a high velocity.This phenomenon includes four phases: impact,drag,cavitation and exit of the fragment.The impact of the fragment and the growth and collapse of the cavity will cause a large pressure to act on the wall of the container,causing damage to the container.When double fragments impact the container,the superimposed pressure formed in the liquid will aggravate the damage of the container.If the aircraft fuel tank is impacted by high-velocity fragmentation,it can cause catastrophic consequences.To study the cumulative effect of HRAM,the process of double high-velocity fragments impact the liquid-filled tank was analyzed using experimental and numerical methods.The characteristics of the cavity,the pressure distribution and superposition characteristics in the liquid,and the walls damage were analyzed.The influence of the impact velocity,the distance between the fragments,impact time interval of double fragments,liquid type and number of fragments were considered.The results show that when the double fragments impact the liquid-filled container simultaneously,the larger the impact velocity,the greater the drag resistance,the faster the velocity decay,the larger the cavity formed,the peak pressure and the specific impulse in the liquid.The larger the pressure pulse duration is,the shorter the deformation of the front and rear wall and the damage degree increase with the increase of the impact velocity of the fragment,and the damage of the rear wall is more serious than that of the front wall.When the impact velocity of the fragment keeps constant,as the distance between the two fragments decreases,the more the two cavities overlap,the larger the radius of the cavity on the other side increases;the pressure field formed by the movement of the two fragments in the liquid increases with time and when those pressure meet,the superimposed pressure value increases with the decrease of the distance between the fragments.The superimposed pressure at the same position is 1.4~2.0 times of the unsuperimposed pressure;the smaller the distance between the two fragments,the more serious the damage of the rear wall.When the two fragments impact the container successively,the pressure in the liquid is smaller than that of the two fragment impact simultaneously,and the pressure field formed by the latter fragment affects the shape of the previous cavity;the impact time interval of the fragments increases,and the degree of wall damage decreases first,and then the wall deformation will remain unchanged.When the double fragments move in different liquid media,the larger the density of the liquid medium,the greater the drag resistance the slower the growth of the cavity length,the cavity diameter is independent of the liquid medium;the pressure in different liquid media is different,the pressure in water is greater than that of diesel and aviation kerosene.The wall damage caused by the fragments impact the water-filled container is more serious than of the container filled with diesel and aviation kerosene.When the total kinetic energy of the fragments is the same,the fragment number is different,the fragments are close to each other and they can penetrate the exit wall,the more of the fragments,the more serious the wall damage would be caused.