The chemical-gas dynamic mechanisms of pulsating detonation wave instability

The chemical-gas dynamic mechanisms behind the instability and failure of a one-dimensional pulsating detonation wave driven by a three-step chain-bra nching reaction are revealed by direct numerical simulation. Two types of p ulsating instability observed experimentally are explained. The first invol ves regular oscillations of the detonation front; where tl-le instability i s driven by low-frequency finite-amplitude compression and expansion waves in the chain-branching induction zone between the main reaction layer and t he detonation shock. For irregular oscillations of the front, the instabili ty mechanism first involves a decoupling between the shock and main reactio n layer. Subsequently, the main reaction layer accelerates, drives a compre ssion wave ahead of it, and undergoes a transition to detonation. This inte rnal detonation wave overtakes the lead detonation shock, generating a new high-pressure detonation, which rapidly decays. A smaller-amplitude pressur e oscillation occurs during the decay with a mechanism reminiscent of that observed for the previous regular oscillation, before the detonation and ma in reaction layer once again decouple and the instability cycle is repeated . For failure scenarios; the sl-lock temperature is observed to drop to the cross-over temperature for the chain-branching reaction, causing the main reaction layer to decouple and retreat indefinitely from the detonation sho ck.