C. E. Frouzakis, A. G. Tomboulides, P. Papas, P. F. Fischer, R. M. Rais, P. A. Monkewitz, and K. Boulouchos, , "Three-Dimensional Numerical Simulations of Cellular Jet Diffusion Flames," Proc. 30th International Symposium on Combustion, Chicago, July 25-30, 2004, . Also Preprint ANL/MCS-P1173-0604, June 2004. [pdf]
Recent experimental investigations have demonstrated that the appearance of particular cellular states in circular non-premixed jet flames depends significantly on a number of parameters, including the initial mixture strength, reactant Lewis numbers, and proximity to the extinction limit (Damk÷hler number). For CO2-diluted H2/O2 jet diffusion flames, these studies have shown that a variety of different cellular patterns or states can form. For given fuel and oxidizer compositions, several preferred states were found to coexist, and the particular state realized was determined by the initial conditions. In order to elucidate the dynamics of cellular instabilities, circular non-premixed jet flames are modeled with a combination of three-dimensional numerical simulation and linear stability analysis (LSA). In both formulations, chemistry is described by a single-step, finite-rate reaction, and different reactant Lewis numbers and molecular weights are specified. The three-dimensional numerical simulations show that different cellular flames can be obtained close to extinction and that different states coexist for the same parameter values. Similar to the experiments, the behavior of the cell structures is sensitive to (numerical) noise. During the transient blow-off process, the flame undergoes transitions to structures with different numbers of cells, while the flame edge close to the nozzle oscillates in the streamwise direction. For conditions similar to the experiments discussed, the LSA results reveal various cellular instabilities, typically with azimuthal wavenumber m = 1-6. Consistent with previous theoretical work, the propensity for the cellular instabilities is shown to increase with decreasing reactant Lewis number and Damk÷hler number.