FLAMELET-VORTEX INTERACTION AND THE GIBSON SCALE

Under certain circumstances a flamelet interacting with a vortex can u ndergo a topological transformation whereby a connected double spiral flame produces a detached pocket of unburned fuel. The dependencies of the detachment time on the parameters of the vortex flow and of the f lamelet are obtained by numerical integration of the eikonal equation. These dependencies are then used in a simple phenomenological model o f small-scale turbulence leading to the definition of a topologically critical length scale-the detachment scale l(D). The detachment scale is found to be nearly proportional to the Gibson scale. Vortices of si ze larger than l(D) can generate short-lived double spirals on the fla melet that give rise to detached pockets of unburned fuel. Vortices of size smaller than D-l simply wrinkle the flamelet. These pockets and double spirals and these wrinkles can all have fractal properties with significant effects on the turbulent flame speed. (C) 1997 by The Com bustion Institute.