Nonuniformities

An understanding of the response of a premixed flame to nonuniformities in the gas flow is important in many technological situations. To sustain a flame in a high-velocity stream the turbine engineer must provide anchors, and these generate strong shear. The designer of an internal combustion engine is concerned with the burning rate in the swirling flow of the mixture above the piston. Turbulence is ubiquitous; then the flame is subject to highly unsteady shear and strain. These situations are extremely complicated and it is unlikely that mathematical analysis will ever provide detailed descriptions; those must be left to empirical studies augmented by extensive numerical computations. Nevertheless, analysis of the response of a flame to a simple shear, for example, can provide useful insight into the interaction mechanism in more complex situations.

Moreover, there are simple circumstances in which such an analysis has direct significance. A burner flame is subject to shear in the neighborhood of the rim, and its quenching depends on the local character of that shear. A flame immersed in a laminar boundary layer experiences both shear (due to velocity variations across the layer) and strain (due to streamwise variations) and its quenching will depend on their local values.