Effect of wall roughness on flame acceleration and deflagration-to-detonation transition in a narrow channel

Numerical simulations are conducted to investigate the effect of wall roughness on flame acceleration (FA), deflagration-to-detonation transition (DDT), and detonation propagation in a narrow channel filled with stoichiometric hydrogen-air mixture. The wall roughness is determined by the element height h relative to the pipe diameter d and can be described using a dimensionless number Ra 1/4 2h/d. A high-order numerical algorithm is employed to solve the Navier-Stokes equations on an adaptive mesh. The results show that the roughness enhances the effect of boundary layer and promotes FA and DDT. In channels with small roughness (Ra<0.1), detonation is not observed. Flame instabilities are caused by the interaction between the flame surfaces and reflected waves from the sidewalls, wrinkling of the flame front, leading to additional flame acceleration, and the production of intense pressure waves. In comparison, in channels with large roughness (Ra>0.1), vortices, shears, and even turbulence are produced in the cavity-like regions as leading shock passes over the elements. The mechanisms of the final detonation transition in the rough narrow channel are thought to be the formation of local hot spots arising from the multiple interactions of shocks with the roughness elements and viscous heating of unburned gas in the highly turbulent boundary layer.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.