Numerical investigation on the impact of barrel gap and length on the internal flow field of electromagnetic launch

Electromagnetic launch utilizes electromagnetic force to accelerate projectiles in the barrel. The high-speed projectile induces complex flows dominated by choking in the barrel, which causes a sharp increase in the air pressure and temperature, deteriorates the working environment, and affects the barrel's service life. The three-dimensional numerical model adopted by the dynamic mesh method is established, and the flow field in the barrel is calculated. Moreover, the influence of the gap and length of the barrel is discussed and analyzed. The research results indicate that the flow is choking during the projectile's acceleration, and precursor and tail shock waves are generated in the front of and behind the projectile, respectively, leading to impacts with pressure exceeding 8 MPa and temperature exceeding 3500 K to the inner walls of the barrel. The pressure at the projectile head, aerodynamic drag, and the shock stand-off distance of the precursor shock consistently rise, whereas the tail pressure initially decreases before increasing. As the gap in the barrel expands, the precursor shock diminishes in strength while the tail shock intensifies. When the speed is the same, an increase in barrel length leads to a greater shock stand-off distance of the precursor shock wave and a longer propagation distance of the tail shock wave, while the pressures at both the head and tail, along with aerodynamic drag, stay the same. These results provide important information for designing barrels, protecting components, and assessing launch efficiency.