Effects of muzzle brake geometry on near field shock evolution and wall force impulse in a cased telescoped ammunition rarefaction wave gun

A cased telescoped charge configuration and rearward gas ejection in a rarefaction wave gun jointly modify pressure release before and after projectile muzzle exit, producing an underexpanded central jet, multiple lateral jets, and strong shock–wall interactions inside the muzzle brake. To clarify how brake geometry governs transient flow topology and momentum redistribution, a three-dimensional unsteady viscous compressible flow model with two-way data exchange between the interior ballistic and computational fluid dynamics solvers was developed for impact–reaction, reaction, and impact muzzle brakes. The three brakes generated dispersed lateral discharge after pre-expansion, sustained multi-row high-pressure discharge, and concentrated baffle impingement, respectively. The impact–reaction brake produced dispersed side jets and compression waves, whereas the reaction brake yielded a larger lateral discharge fraction and a wider compound wave region. The impact brake formed a concentrated stagnation-pressure zone, strong reflected compression structures, and highly directional jets. Peak axial forces on the principal braking surfaces were 41.61, 57.97, and 110.48 kN, with corresponding impulses of 64.39, 106.42, and 113.92 N s. Although the impact brake produced a peak force 1.91 times that of the reaction brake, its final impulse was only 7.0% higher, demonstrating the combined importance of load magnitude and duration. Rearward gas ejection reduced recoil impulse from 1720.36 to 352.27 N s; adding the three brakes further reduced it to 287.88, 245.85, and 238.35 N s, corresponding to recoil-reduction efficiencies of 83.27%, 85.71%, and 86.15%. These results link brake geometry to shock topology, wall loading, and impulse accumulation.