NUMERICAL STUDY OF UNSTEADY TURBULENT PREMIXED COMBUSTION - APPLICATION TO FLASHBACK SIMULATION

Numerical simulation of combustion phenomena such as flashback involve s complex interactions between acoustics, turbulence, and combustion. An approach is proposed which combines a large eddy simulation (LES) t echnique with an adapted flame representation for premixed combustion. The standard Smagorinsky model is used for the subgrid closure. The f lame is artificially thickened so that it can be resolved on the LES m esh. Two-dimensional nonreactive computations are first performed in a backward facing step configuration. Spectral analysis of the pressure and velocity signals recorded during the calculations are compared wi th experimental results. The mechanism of flashback linked to combusti on instabilities in a sudden expansion configuration is then investiga ted. The effects of the instabilities are simulated by imposing an ext ernal velocity modulation at the entrance of the computational domain. Two cases are discussed which illustrate the dynamics of the flame. U pstream propagation is observed in response to strong flow perturbatio ns. (C) 1998 by The Combustion Institute.