The Beauty of Turbulence and Transitions in Reactive Flows Elaine S. Oran

摘要

The most complex and difficult problems in fluid dynamics involve transitions among what seem to be relatively stable states. When these systems also involve energetic interactions, as caused by nuclear or chemical reactions, the results can be dramatic and unexpected. Such reactive-flow transitions are critical elements in the working of systems ranging from engines for propulsion, to accidental fuel explosions, to explosions of thermonuclear supernova, and arguably to the primal explosion that created the universe. Two very different regimes of chemically reacting flows will be described in this presentation. The first involves high-speed flows with turbulent flames and possible transition to detonation. For this type of turbulent reactive flow, numerical simulations coupled to available experiments have played an important role in understanding the mechanisms, structure, and dynamics. The second regime is a purely subsonic flow that involves a transition from a fire whirl to a small, soot-free, totally blue flame, the blue whirl. The transition to a blue whirl occurs when the turbulence in the fire whirl reaches a level of intensity that allows vortex breakdown, and it appears as a transition from turbulence. The blue whirl is "new territory," and experiments, simulations, and theory are all trying to understand the properties and limits of this strange, intensely blue, soot-free flame that burns so efficiently.