Direct numerical simulation of a realistic acoustic wave interacting with a premixed flame

Abstract

The interaction of an acoustic wave with a turbulent flame and its consequences are still not well understood at present time. In the present paper the interaction of a syngas turbulent premixed flame with an acoustic wave is considered. At the difference of previous publications, a realistic, sinusoidal acoustic wave is considered for several periods. The interaction process is investigated by Direct Numerical Simulations (DNS) involving detailed physical models, so that an excellent accuracy is obtained. The DNS computations are systematically carried out twice, once with and once without adding an acoustic wave at the inlet, all other conditions being fixed. By a difference between both results, it is possible to quantify the interaction process. Local amplification, damping and structural modifications of the initially planar acoustic wave can be identified and analyzed. Moreover, a possible influence of the direction of propagation (acoustic wave reaching the flame from the fresh or from the burnt gas) has been investigated. Since a detailed reaction scheme is employed, the effect of each individual species on the wave amplification or damping can be quantified through the local Rayleigh’s criterion. It can be proved that the direction of propagation has no influence, confirming that amplification or damping is in the mean mainly controlled by the coupling process between pressure and heat release fluctuations through the chemical reactions. For the present case, species CO2, H and H2O mostly control wave amplification, while species O, OH and CO dominate damping. Two different reaction mechanisms have been employed and deliver almost identical results. The local version of the classical Rayleigh’s criterion presented in previous works is extended to take into account flame movement, which is now noticeable. Nevertheless, the results prove that the variation of flame position with time has a negligible influence on the coupling mechanism.