Multiscale techniques in Premixed Flames

Department of Mechanical Engineering & Materials Science Seminar

Multiscale techniques in Premixed Flames 
Jose Grana-Otero
University of Kentucky
Department of Mechanical Engineering

The dynamics of premixed flames is paradigmatic of highly nonlinear physical phenomena. Their multiscale nature and the complex chemistry of the oxidation of common fuels contribute significantly to this complexity. Nevertheless, this multiscale nature can be judiciously exploited in order to assist in sim- plifying problems and uncovering the essential physics. In addition, reduced yet realistic kinetic schemes permit to reproduce their essential chemical structure while still keeping a semi-analytical treatment reasonable. Two examples using these techniques are presented.

The first one is the analysis of the unsteady dynamics of pulsating planar premixed flame fronts in a reactive solid. In this mode, the propagation assumes the form of extremely nonlinear relaxational type pulsations. It is shown how the problem for the unsteady propagation of these fronts can be reformulated as the dynamics of an infinitely thin surface, the so-called reaction layer where chemical reactions are confined, that is embedded in reactions-free regions. The analysis of the inner structure of the reaction layer provide the coupling conditions that the reaction-free solutions on each side of the reaction layer must satisfy on it. This new simplified formulation allows to discover key aspects of the nonlinear dynamics of the propagation of these pulsating fronts.

As a second example, the effect of the flow strain and flame curvature on the propagation velocity of a premixed flame will be analyzed. Again, the multiscale structure of the problem allows to precisely understand the role of kinetics. In particular, it is shown that, contrary to what is found with simple one-step Arrhenius kinetics, two Markstein numbers are needed to generically describe these effects when more realistic reduced kinetic schemes are considered.

Wednesday, February 18, 2015
2:30 – 3:30 p.m. 
Location: Mason 107 (9 Hillhouse Avenue)
Host: Professor Alessandro Gomez
Refreshments served at 2:15 pm