Mach reflection of detonation waves over a porous concave wedge

Abstract

An experimental study of the differences in the Mach reflection process over smooth and porous concave wedges was systematically performed based on soot track measurement. Meanwhile, the interaction mechanism among the incident detonation, the Mach stem, and the porous wall was analyzed in detail. The results show that introducing multiple pores on the concave surface induces an additional attenuation region. In contrast, the triple-point over porous wedges starts traveling later and ends up colliding with the concave surface earlier. Moreover, the Mach stem height is shorter at the same wall position. For the transition angle of Mach-to-regular reflection over porous wedges, it is found to be negatively correlated with the length-scale ratio R/λ of the radius of curvature (R) to the cell size (λ), gas instability, and porosity. Although the experimental transition angle disagrees with the Chester–Chisnell–Whitham (CCW) and the reactive CCW theories, it is in agreement with the trend over smooth wedges that the experimental transition angle approaches to reactive CCW theory as R/λ increases. For the triple-point trajectory, it is almost a straight line when wall angle θ≤30° at R = 522 mm. It is also found that the triple-point trajectory is similar at the beginning for different mixture compositions at an equivalent initial pressure. The height of the Mach stem is shorter over a porous wedge with higher porosity, but it reaches a maximum value at a wall angle of 30° for wedges. Moreover, the Mach stem height decreases with increasing initial pressure or gas instability.