Numerical investigations on behaviour bifurcation of premixed H₂-air flames in mesoscale tubes

Unsteady numerical simulations with detailed kinetic chemistry have been reported for premixed H₂-air flames in straight mesoscale tubes of various diameters to understand the effect of wall heat transfer conditions on flame transition and behaviour bifurcation leading to a change in flame shape and flame propagation velocity. A parabolic velocity profile is applied with no-slip boundary conditions at the walls. For certain wall heat transfer conditions, it was observed that the flame transforms from a concave- to convex-shaped flame during propagation through the channel, accompanied by a change in flame propagation speed, heat of reaction and heat release rates. The transition in flame shape is attributed to thermal wall coupling effect through wall heat transfer to surroundings, which affects the flow redirection in the vicinity of the flame due to heat-loss, resulting in flame behaviour transition. Due to these flame behaviour transitions, the heat release rates and flame propagation velocities change significantly as discussed in this paper.