Flat-Fire Trajectory Simulation of AK-47 Assault Rifle 7.82-mm Bullet

The present work discusses the computation of the trajectory of a projectile with flat-fire trajectory approximation. The test case corresponds to 7.82-mm bullet of assault rifle AK-47. Initially, computational fluid dynamics (CFD) simulations are performed over the bullet with commercial CFD software, ANSYS Fluent. Density-based solver is employed to solve coupled continuity, momentum, and energy equations for Mach number of 2. The corresponding velocity of bullet is 680 m/s. The effect of turbulence on flowfield is accounted by using k-ε turbulence model. Flow features over the bullet and associated surface pressure distribution obtained from the simulations are explained. Predicted drag coefficient of bullet is validated against available experimental data, and the deviation is below 5%. Flat-firing approximation is used for simulating the trajectory of the bullet for which drag coefficient is an input parameter. Initially, the flat-fire trajectory code is validated against published trajectory data. The error between the predicted velocity and published data is below 0.05%. Next, flat-fire trajectory simulation is performed for bullet. Velocity, range, and height of the bullet are predicted as a function of time. It is found that the bullet travels a distance of 280 m before hitting the ground. During the course of travel, there is 33% reduction in its velocity and corresponding flight time is 0.63 s. The effect of variation in density with respect to altitude on range of bullet is also investigated. Range of the bullet at 4 km altitude is 16% higher than that of sea level.