Detonation Diffraction in Divergent Channels with Smooth and Porous Walls

An experimental study of the diffraction and re-initiation of detonations in divergent channels in [Formula: see text] was reported in this paper. Both smooth and porous divergent walls were used in this study. Two re-initiation modes, termed re-initiation from expansion wave front and lower wall, were detected. Two kinds of transverse detonations were observed, one propagating toward the lower wall ([Formula: see text]) and the other toward the top wall ([Formula: see text]). For re-initiation from the expansion wave front, the re-initiation is due to [Formula: see text] and the influence of the wall condition can be ignored. For re-initiation from the lower wall, the re-initiation is mainly due to the Mach stem and [Formula: see text]. The reflection point distance for re-initiation from the lower wall is [Formula: see text] (smooth wall) or [Formula: see text] (porous wall) ([Formula: see text] is the detonation cell size). The delay initiation over a porous wall is ascribed to the diffraction of Mach stem detonation. Three collision modes of re-initiation from the lower wall were determined based on the collision between [Formula: see text] and [Formula: see text], i.e., subcritical collision as [Formula: see text], critical collision as [Formula: see text], and supercritical collision as [Formula: see text] ([Formula: see text] is inlet channel width). The collision point distances are approximately [Formula: see text] for the smooth wall and [Formula: see text] for the porous wall.