Chapman-Jouguet oblique detonation structure around hypersonic projectiles

How to generate a steady-state detonation around a hypersonic projectile in stoichiometric hydrogen-oxygen premixed gases is studied. The speed of the hypersonic projectiles was beyond the Chapman-Jouguet (C-J) detonation speed. The flowfield around the projectile was visualized by using a gate intensified charge-coupled device camera (single-frame schlieren pictures and OH radical self-emission images). Three parameters are varied: 1) the projectile flight length from diaphragm rupture location, 2) the initial pressure of mixture below/above the critical pressure for steady detonation initiation around a hypersonic projectile, and 3) the projectile speed. At the pressure condition below the criteria, the detonation structure is composed of three different shock and detonation waves, which appear just after a diaphragm rupture and evolve in time: an overdriven bow detonation wave, a strong detonation wave, and a diffracted shock wave. Their propagation after diaphragm rupture is investigated, and it is found that the C-J detonation wave moved away from the projectile and only a reactive bow shock wave remained around projectile far away from the diaphragm. At the pressure condition above the criteria, a steady oblique detonation wave was generated around the projectile as soon as the projectile broke the diaphragm. in this steady-state detonation-wave case, with respect to the flow Mach number behind the wave front, the whole detonation wave was divided into four parts: I) strong overdriven detonation wave, 2) weak overdriven detonation wave, 3) quasi-C-J detonation wave, and 4) C-J detonation wave. It has been found that a rarefaction wave is generated at the projectile shoulder and that curvature of the wave has a significant effect on the structure of the detonation wave.