Triple flames in swirling flows

Recent work has shown that the blue whirl, a soot-free hydrocarbon flame, is comprised of a triple flame in a swirling flow undergoing vortex breakdown. This paper describes three-dimensional, numerical simulations of triple flames in swirling flows with and without vortex breakdown and relates this to what is known about the blue whirl. The results for three swirl numbers are presented, all of which develop a triple flame. The shape of the triple flame, however, differs depending on whether there is vortex breakdown and its location. Changes in vorticity before and after ignition are examined for each case. The analysis shows that for the lowest swirl number, the effect of volume expansion dominates and mitigates vortex breakdown. Increasing swirl results in vortex stretching and tilting becoming dominant and promoting vortex breakdown. Which of these effects is dominant determines the flow structure and then the flow structure determines the different flame shapes. Insights gained from this work and their relation to the blue whirl are discussed.