Investigation on the dynamics of shock wave generated by detonation reflection

Abstract

When a detonation wave hits a rigid wall, a reverse shock is created. This occurrence is common in closed pipe detonation experiments. To better comprehend the propagation dynamics of the reverse shock, experiments were performed in a 2.5-meter-long detonation tube. Normal reflection, Mach reflection, and regular reflection of detonation are generated by changing the end-wall profile. Three different mixtures, 2H₂+O₂+40%Ar (with very regular cellular pattern), C₂H₄+3O₂+40%Ar (regular), and CH₄+2O₂ (irregular), are used to examine how detonation stability affects the subsequent reflected shock propagation procedure. The reflection process is visualized by using a high-speed schlieren imaging technique. A one-dimensional simulation with a detailed chemical reaction mechanism was employed to further illustrate the dynamics of the reflected shock, which is generated by detonation normal reflection. Results show that the variation of the reflected shock speed in normal reflection can be categorized into three phases. First, the reflected shock speed rapidly decreases in the detonation reaction zone. It then slowly increases due to the transmitted expansion wave. Finally, the shock wave velocity gradually decreases in the stationary flow. A post-shock blast wave appears in the shocked but unburnt mixture. However, its impact on the reflected shock structure is minimal, as it attenuates drastically. The collision of the detonation and the shock-shock interaction at the tip of the reflectors boosts the reflected shock speed, and the acceleration ratio in the two regular mixtures is 33.7 %–48.7 %, while it is approximately 20 % in the irregular mixture. This study offers a fresh perspective on the complex detonation reflection process through the combined analysis of both experimental and numerical results.