Design and analysis of a spin stabilized projectile using magnetic resonance velocimetry

At the end of flight, spin stabilized projectiles tend to experience dynamic instability resulting in tumble and reduced aerodynamic and terminal ballistics effectiveness. This instability is largely attributable to an increase in magnitude of the Magnus moment and transient fluctuations of the same coefficient as the projectile decelerates into the transonic flight regime. Computational fluid dynamics (CFD) simulations struggle to accurately predict the Magnus moment in these cases. This work leverages magnetic resonance velocimetry (MRV) to obtain a high-fidelity, three-dimensional velocity field data set around a projectile spinning at constant rotation with sub-millimeter resolution. A modified M193 5.56 mm projectile was specially designed and built to thicken the hydrodynamic boundary layer for analysis. The experimental rig rotated the projectile at constant spin rates in a constant flow of copper-sulfate solution as part of a test section placed within a research-grade MRI magnet. The velocity fields for several spin rates and projectile angles of attack were analyzed to identify and verify proposed causes of the Magnus moment, particularly boundary layer asymmetries and attached lee side vortices. The data was also compared to Reynolds Averaged Navier-Stokes CFD simulations to improve numerical modeling schemes.