Aerodynamical Computational Fluid Dynamics Study of a non-lethal 12-gauge fin-stabilized projectile

Nowadays, the trajectory model for a subsonic fin-stabilized projectile at low angle of attack is typically a point-mass model (PMM), taking only gravity and a constant zero-yaw drag into account. This choice can be qualitatively justified for non-lethal projectiles given the short ranges. The disadvantage of this approach is the lack of prediction on the precision and the attitude of the projectile when hitting the target, because of a possible instability in flight. However, the use of non-lethal projectiles requires that the impact conditions are met, otherwise more serious injuries may occur. Therefore, the consideration of other forces and moments acting on the projectile in flight is mandatory to predict static and dynamic stability, already in the body shape design as well as in the controller design process in the field of non-lethal ammunitions. Starting from a geometry in caliber 12-gauge, static coefficients (drag, lift and pitch) for different angles of attack using steady RANS-simulations with a low-order turbulence model were found. Different trajectories were then analysed using those coefficients and the difference between the PMM and a 3-DOF accounting for drag, lift and pitch in function of the angle of attack is indeed negligible in height and in range as long as the launch conditions are completely undisturbed. The slightest destabilization makes the PMM completely inappropriate. Knowledge of the pitch damping coefficient then becomes a necessity to optimize stabilization following minor disturbances.