A new rapid deflagration-to-detonation transition in a short smooth tube

Abstract

Obtaining a rapid deflagration-to-detonation transition (DDT) within a short smooth tube is a challenging task. Here, an unconventional means of flame acceleration propagating upstream in subsonic and supersonic mixtures within a smooth tube was introduced to acquire a speedy DDT. The Navier–Stokes equations with an adaptive mesh refinement technique and a detailed hydrogen–air chemistry reaction mechanism of 11 species and 27 steps were utilized to resolve the entire DDT characteristics. The effect of the initial Mach number on flame acceleration and DDT mechanism was revealed comprehensively. The results demonstrated that a prompt oblique shock wave (SW) occurs when the flame propagates upstream along the boundary walls due to the boundary layer influence. An intense coupling between the SW and the leading flame front is enhanced by increasing the initial Mach number of the mixture. The speedy generation of the oblique SW is formed at the incipient stage, mainly produced by the boundary layer influence and the coalescences of the compression waves. Consequently, the run-up time to detonation is shortened accordingly through a fierce reflected SW due to the intense leading SW after it reflects from the confined wall. Furthermore, three kinds of DDT evolution are revealed from the obtained results: (1) localized ignition in the upper boundary wall after the reflected and transverse shock waves propagate in the upper wall regions; (2) autoignition is formed in the confined wall corner after the reflected SW; and (3) direct detonation transition occurs at the end wall behind a strongly reflected SW in the supersonic case.