Velocity behavior downstream of perforated plates with large blockage ratio for unstable and stable detonations

Abstract

Due to the excellent thermal propulsion performances of detonation, it has been applied for the purpose of aerospace propulsion devices, e.g., pulse detonation engines (PDEs), rotating detonation engines (RDEs), and oblique detonation wave engines (ODWEs). However, it remains challenging for developing those new-concept propulsion devices, mainly because it is a formidable task to establish a steady and self-sustained detonation in the hypersonic flow and combustible mixture. One of the fundamental problems is to understand the interaction of diffractions and the detonation waves within the engines. In this study, perforated plates with various blockage ratios are seated at the beginning of the detonation propagation to explore the diffractions that generated from the plates on the detonation propagation mechanism. Two explosive mixtures of C2H2 + 5N2O and C2H2 + 2.5O2 + 70% Ar are studied to illustrate the difference in propagation velocity behavior of detonation after it suffers from large-scale diffractions. The results show that diffractions have less effect on the propagation of highly unstable mixture, and the effect becomes obvious as BR increases to 0.962; this phenomenon occurs because detonation has an irregular cellular pattern and sub-structures are characterized by highly unstable detonation, in which the detonation instabilities are amplified by the large perturbations of obstacles, leading to an augment in forming more cellular cells of detonation in its front that cover the weakening effects from diffractions. In contrast, the diffractions significantly affect the stable mixture, manifested by a remarkable increase of the critical pressure for a self-sustained detonation downstream of the obstacle with the augment of blockage ratio; this phenomenon can be attributed to the diffractions being distributed along the curvature over the detonation surface, thereby causing more excessive curvature of the entire detonation front, which in turn exacerbates the failure of detonation.