Numerical Modeling of Turbulent Combustion

L. Talbot, R. K. Cheng, and I. G. Shepherd, Lawrence Berkeley National Laboratory
C. K. Chan, Hong Kong Polytechnic University

Research Objectives

The objectives of this research are threefold:

1. To model numerically the dynamics of premixed flame surfaces in the reaction sheet regime.
2. To determine the modification to flow turbulence produced by such flames.
3. To determine the effect of turbulence on flame shape, speed, and thickness.

Computational Approach

The random vortex method is combined with the level-set formulation for the tracking of propagating surfaces under curvature to model the dynamical behavior of turbulent premixed flames, including baroclinic vorticity generation.

Accomplishments

Significant improvements to our earlier work on dynamical behavior of a premixed open V-flame were achieved in the form of better simulation of the inflow-outflow boundary conditions and better statistical resolution of the dynamical properties of the flame, including turbulence generation, Reynolds stresses, and flame motion, with good agreement with experiment. These results, including comparisons with experimental data obtained by us at Berkeley Lab, will be reported in a forthcoming publication.

Significance

A major technological combustion problem is the design of more energy-efficient, low-emission industrial and home-heating turbulent-flame gas burners. In the design of such burners, a primary objective is to achieve stable combustion under the most fuel-lean conditions possible, since the leaner the flame, the lower the maximum temperature and the lower the amount of NO_x produced. The limit of stable lean flame operation is directly related to the effective turbulent-burning velocity. Thus, it would be of great benefit to designers of premixed turbulent-flame burners to have at their disposal a numerical model that reliably predicts turbulent-burning speed, flame configuration, and other related quantities as a function of reactant turbulence intensity and effective heat release.

Publications

C. W. Rhee, L. Talbot, and J. A. Sethian, "Dynamical behavior of a premixed open V-flame," J. Fluid Mech. 300, 87-115 (1995).