Experimental analysis and large eddy simulation to determine the response of non-premixed flames submitted to acoustic forcing

Large eddy simulations appear to be a very promising tool for describing combustion instabilities but, because these instabilities generally involved acoustic waves through the whole system, relevant simulations are currently still impossible. An intermediate step is to use large eddy simulation of the burner only to estimate the parameters of the so-called n-tau model where the flame is viewed as inducing an amplification, n, with the time delay, tau, to the velocity perturbation. These parameters are then incorporated in a global acoustic model of the system to determine whether combustion instabilities may occur or not. The objective of this study is to investigate the ability of large eddy simulations to determine the n-tau parameter. An experimental turbulent non-premixed flame is submitted to acoustic perturbations induced by loudspeakers. The flame transfer function is then determined, and n and tau are computed as a function of the downstream location in the burner. n and tau are also extracted from large eddy simulations of the same burner submitted to velocity perturbations. The results are very promising because numerical and experimental data are in good agreement.