Numerical investigation of self-sustaining modes of 2D planar detonations under concentration gradients in hydrogen–oxygen mixtures

Abstract

Self-sustaining modes of detonations in non-uniform mixtures for hydrogen and oxygen are numerically studied. Concentration gradients are set vertical to the direction of detonation propagation, with equivalence ratios decreasing from rich values to lean ones. High-resolution codes based on the fifth-order weighted essentially non-oscillatory (WENO) scheme in spatial discretization and the 3rd-order Additive Runge-Kutta (ARK) schemes in time discretization, with detailed chemical kinetics model, are developed. Two-dimensional (2D) numerical simulations are conducted in a 2D planar geometry, non-uniform distributions are then precisely controlled as a function of width. The cellular structures and transmissions, failure and re-initiation mechanisms of detonation fronts are characterized. Results show that the low concentration gradient produces the multi-head mode of detonation with continuous adaptation of velocities and multicellular structures to local concentration. The high concentration gradient generates single-head mode with detonation re-initiation at channel walls produced by reflected transverse Mach waves. Specially, the intermediate distribution between the low and high concentration gradients induces an alternation mode between singe-head and multi-head detonations.