Numerical Investigations On The Dynamics Mechanism Of Muzzle Flow

During the gun firing process, a complicated muzzle flow field will be formed after the high-pressure and high-temperature propellant gas exits the muzzle. A series of harmful phenomena occur throughout development of the muzzle flow, such as muzzle blast and flash, the perturbation of the projectile velocity. The dynamics process and affecting factors of muzzle flow need to be studied in order to improve the weapon performance and control the hazards.The numerical and experimental methods are employed to study the complex phenomenon of muzzle flow and its affecting factors. Time-dependent Navier-Stokes equations with chemical reaction, which were cast in the Arbitrary Lagrangian-Elerian (ALE) framework, are used in the numerical investigations. Finite volume method is used for space discretization. The flux across the cell interface is calculated by using AUSM+scheme, solutions are advanced in time by explicit two step Runge-Kutta method, and the C-H-O-N reaction mechanism with9components and12elementary reactions is performed to solve the reacting source terms, and MPI method is used for the parallel computing.1) The effect of precursor flow on the propellant flow field is investigated based on the numerical results. It shows that, the bow shock is produced because of the directivity of precursor flow. The propellant gas expanding velocity in the axial direction is much higher than in the radial direction in the early stage. And the maximal stagnation pressure in the area near the muzzle withe considering the precursor flow increases by twice more than that without considering the precursor flow.2) Perturbation of the projectile velocity in the after effect period is calculated under different conditions. The results indicate that the velocity reaches the maximum value after the projectile crosses the Mach disk, which could be increased more than3%on the muzzle velocity. The charge weight exerts little effect on the rate of velocity change, and the projectile mass scale is almost linear with the rate of velocity change.3) Under the calculation condition, there are two stages for the chemical reaction in the muzzle flow. In the first stage, the reaction takes place in the vortex rings in the side of the jet flow. In the second stage, the boundary layer separates from the vortex ring and the K-H instability is caused by the shear layer, and the reaction area moves to the downstream of the Mach disk which is near the axis. Nozzle has two effects on the muzzle reacting flow:first, the strength of Mach disk is decreased with reduction of gas temperature after the expansion in the nozzle; second, the jet contact surface is more stable, which suppresses the mixing of propellant gas and air in some extent.4) Based on the experimental and numerical results, the investigation on the overpressure of muzzle blast with different ambient pressure is performed. Both of them reveal that the overpressure of the muzzle blast is almost linear with the ambient pressure within a certain range. When the gun is in supersonic incoming flow, the muzzle shock wave is limited in a cone-shape area, and the overpressure value in this area is much higher than that in the static environment.