Triple flames in vortex flows *

The blue whirl is a lifted, laminar, whirling, blue flame that burns liquid hydrocarbon fuels with no soot production. It was first created in a laboratory when a relatively large, swirling fire whirl intensified before spontaneously making a transition to a blue whirl. Recent work has shown that vaporized fuel can also create a blue whirl, and that key components of the blue whirl consist of a triple (tribrachial) flame in a vortex flow and a bubble mode of vortex breakdown. To try to understand how we might create the blue whirl in a safer, more controlled way, we focus on the basic interaction between vortex flow and energy release from combustion reactions and how it leads to a flame with the structure of a blue whirl.  Here we present the results of three-dimensional numerical simulations of vortex flows with triple flames in gaseous heptane-air mixtures. We show the effect of swirl number on the final flow pattern and flame structure and analyze the effects of vorticity interactions with the triple flames.