Computational Fluid Dynamics Analysis of Drag Reduction in Bullet via Geometric Modifications

Abstract

In the field of external ballistics, the geometry (shape and structure) of the projectile plays a significant role. This geometry affects a multitude of variables, including air resistance, stability, range, and accuracy. The objective of this study was to decrease the drag coefficients by making different geometric alterations to the Spitzer-type ogive bullet and examining the flow conditions, Mach number, and pressure distributions around the projectile using a three-dimensional numerical simulation. Upon examination of the results, it was observed that the flow exhibited subsonic stagnation zones and a velocity drop upstream of the nose tip. The flow became slightly supersonic as it expanded around the ogive nose and boattail junction. Expansion fans and recompression shocks were detected at the points where the ogive-shaped nose of the projectile transitions to the body, where the boattail-shaped rear of the projectile transitions to the body, and at the base of the projectile. The pressure coefficient value reached its maximum value of CP=0.7 when the air decelerated and dropped to CP=-0.5 as the projectile transitioned from the nose to the body. A gradual decrease in pressure along the projectile surface resulted in a more consistent and lower pressure coefficient compared to the nose. The A3-type bullet, including the most extensive spiral groove, exhibited a 12.4% enhancement in drag reduction as compared to the original bullet. The B-series of straight grooves exhibited a considerable decrease in drag. Nevertheless, the efficacy of helical grooves in regulating flow separation at the tail surpassed that of other methods. The A-series bullets, namely A2 and A3, were well-suited for applications that demanded little aerodynamic resistance. The B-series bullets exhibited enhancements compared to the conventional design and may be deemed suitable for more straightforward production or design limitations.