Detonation transmission through compact piping and transition cavities is frequently limited by diffraction-induced shock–flame decoupling, which can lead to either recovery or complete failure depending on the available confinement and reflection history. To clarify these competing outcomes, detonation diffraction, quenching, and re-initiation in a double-bend duct with a variable-width cavity are examined numerically. High-resolution simulations were conducted for gaseous detonations propagating through a double-bend duct containing cavities of different widths. The coupled evolution of the leading shock and the reaction zone was diagnosed using numerical schlieren fields together with pressure and temperature histories to resolve reflection processes and local ignition events. Three propagation regimes were identified, primarily controlled by cavity width. In narrow cavities, the diffraction interval remains short, so the partially decoupled structure is repeatedly reinforced by wall reflections; reflection-induced high-pressure spots can intersect the nearby flame front and maintain a fully coupled (often overdriven) detonation. For intermediate widths, the wave approaches near-failure, yet re-initiation occurs when a reflected shock catches the adjacent flame and a stable triple-wave configuration is established, restoring self-sustained propagation. In wide cavities, prolonged shock -flame separation and strong rarefaction prevent effective shock–flame interaction; the nascent ignition kernel is quenched and global failure follows. The results indicate that recovery hinges on the spatiotemporal alignment between reflection-generated high-pressure regions and the displaced flame front, while geometric expansion governs whether such alignment is achievable. These findings provide mechanistic guidance for designing transition sections in pre-detonators, flame-arresting elements, and detonation-based propulsion ducts by constraining expansion severity and promoting timely shock–flame intersection.
Li et al. (Tue,) studied this question.