Investigation of Vortex-Premixed Flame Interaction with Detailed Chemistry

Abstract

The interaction of a vortex with an initially planar premixed stoichiometric hydrogen-air flame is investigated to characterize the evolution of the vortex across the flame and identify the different regimes of behavior. These characteristics include vortex circulation, peak vorticity, peak velocity, and size. There are two key non-dimensional parameters. The first is the ratio of length scales, l_v/l_F, being the ratio of the vortex diameter to the laminar flame width and the second is the ratio of velocity scales, u_v/S_L, being the ratio of the characteristic velocity of the vortex to the laminar flame speed. The parameter space is explored with values of l_v/l_F ranging from 0.3 to 10 and values of u_v/S_L ranging from 0.1 to 50 corresponding to over 20 separate conditions. By performing simulations which vary these parameters over two and three orders of magnitude, the intermediary and limiting cases of each parameter are investigated. The simulations are performed using a low-Mach number Navier- Stokes solver, detailed hydrogen-air chemistry with 9 species, and unity Lewis number transport. Under stoichiometric hydrogen-air, the assumption of unity Lewis number is justified. Viscous and simulations with a reduced viscosity are preformed highlighting aspects of the coupling of the chemistry and the fluid mechanics. The results demonstrate the existence of four different regimes of the vortex-premixed flame interaction. In the limit u_v/S_L ≫ 1 and l_v/L_F ≫ 1, the vortex wraps the flame within itself and the vortex survives after passing through the flame. In the limit u_v/S_L ≫ 1 and l_v/l_F ≪ 1 the vortex mixes individual layers of the flame within itself and the vortex survives after passing through the flame. In the limit u_v/S_L ≪ 1 and l_v/l_F ≫ 1, the vortex creates sufficient flame curvature to produce baroclinic torque which destroys the incoming vortex. In the limit u_v/S_L ≪ 1 and l_v/l_F ≪ 1, the vortex has negligible effect on the flame and simply stretches in the flame normal direction. All four regimes correspond to qualitatively different vortex flame interactions and therefore the changes in vortices follow different behavior. The use of detailed chemistry for these simulations provides for additional insight into the coupling of chemistry and fluid mechanics in describing the behavior of vortex-premixed flame interactions.

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