A numerical simulation of a vortex convected through a laminar premixed flame

Abstract

A numerical study was conducted to understand how a vortex, when convected at moderate speeds across a premixed flame, can induce velocities that pull the flame along with the vortex, causing flame elongation and unsteady flame stretch. If the vortex-induced velocity that opposes flame motion is sufficiently large, the flame cannot propagate over the vortex and thus temporarily remains attached to the moving vortex. A flame attachment criterion is discussed; when the criterion is met the vortex forms cusps and pockets in the flame structure similar to those observed experimentally. The net result of increasing the vortex convection velocity is to reduce the residence time of the vortex in the flame, which reduces the degree of flame wrinkling. Vortex pairs that exert an extensive strain on the flame were found to have significantly longer residence times of interaction than vortices that exert compressive strain; this difference in residence time helps to explain why extensive strain on a flame is more probable in turbulent flames than compressive strain. The calculated images of the laminar flame shape show encouraging agreement with experiment, which is another indication that flame-interface simulations are a promising way to represent very wrinkled turbulent premixed flames in a numerically efficient manner.