Research On The Characteristics Of Exterior Ballistics And Submunitions' Separation Of Gun-launched Cluster Munition With Beveled Fins

In order to providing reference for the design of cluster munition with beveled fins shot by major caliber smooth-bore gun,taking a cluster munition with beveled fins shot by a 125 mm caliber smooth-bore tank gun as an example,the exterior ballistics characteristics of carrier round and the separation characteristics of disc-shaped submunitions inside which are ejected from carrier round in tandem were researched.The aerodynamic theory and the theory of external ballistics are applied to demonstrate the feasibility of fuze's principle for determining distance by counting revolution of fin-stabilized projectile with beveled fins.The variation laws of spin rate and its equilibrium characteristics,the flight stability of projectile and the separation characteristics of disc-shaped submunitions which are ejected from carrier round in tandem during the flight of the exterior ballistics of fin-stabilized projectile with beveled fins are researched by using the computational fluid dynamics simulation method.The method of determining distance by counting revolution for fuze of fin-stabilized projectile with beveled fins was inspired by the use of this method in fuze of spin-stabilized projectile.The error of determining distance caused by the variation of velocity can be ignored using this method,and the initial velocity of projectile needn't be measured.The results of numerical calculation indicate that variations of the mass of projectile and firing angle have very small effects on precision of determining distance by counting revolution,but the effect of the angle variation of beveled fin is larger.Increasing the angle of beveled fin as large as possible can improve the precision of determining distance by counting revolution and lower the effect of manufacturing error of the angle of beveled fin on the precision of determining distance.Determining distance by counting revolution of low spin rate projectiles can only be applied to medium and large caliber projectiles which the lethality is relatively large in principle.The technique of Fluent dynamic mesh was applied during the simulation computation of the variation laws of spin rate and the equilibrium spin rate of fin-stabilized projectile with beveled fins.The results indicate that the relationship between the equilibrium spin rate of projectile and the free flow velocity is linear if the beveled angle remains the same,the relationship between the equilibrium spin rate of projectile and the beveled angle is linear if the free flow velocity remains the same and the time when the projectile achieves the equilibrium spin rate is independent of both the free flow velocity and the beveled angle.As a case study,the time to achieve equilibrium spin rate for the cluster munition shot by a 125 mm caliber smooth-bore tank gun is about 0.9 seconds.By using the Fluent software,the aerodynamic characteristics of the projectile were analyzed by numerical simulation of the steady flow of the projectile at different free flow velocity and attack angle,and then the static stability of the projectile at different conditions was calculated.The static stability of the projectile increases with the increase of the attack angle and decreases with the increase of Mach number under supersonic conditions.The coupling of the fluid governing equation and the rigid body dynamics equation were solved by combining the technique of dynamic mesh,and then the variation laws of the attack angle were obtained when the projectile was disturbed at he muzzle and after achieving the equilibrium spin rate.The attack angle of the projectile varies periodically with time and the amplitude decays constantly,so the projectile is dynamically stable in these two characteristic trajectory points.By using the Fluent software,the three dimensional rigid body collision model was added through user-defined function to simulate the collision between submunitions.After the numerical simulation of the unsteady flow of the separation between the submunitions combined with the technique of dynamic mesh,it was found that the separation of the tandem submunitions was started from the submunition at the tail.The distance is mainly extended along the longitudinal direction.A certain lateral offset is also formed due to the aerodynamic interference during the separation.The longitudinal displacement of the submunitions after the separation has a quadratic function with time,but no obvious law can be found in the lateral displacement.The longitudinal dispersion in the air is quite uniform,and increases with time increasing.A different detonation delay of submunitions will change the longitudinal distribution in the air after separation,so that the distribution can increase if the submunition at the tail of the tandem submunitions is detonated prior to the head submunitions.