DNS of Intrinsic ThermoAcoustic modes in laminar premixed flames

Recent studies [Hoeijmakers et al. 2014, Emmert et al. 2015] suggest that thermoacoustic modes can appear in combustors with anechoic terminations, which have no acoustic eigenmodes. These modes, called here Intrinsic ThermoAcoustic (ITA), can be predicted with simple theoretical arguments, but have been ignored for a long time. They are reproduced in this paper using Direct Numerical Simulation (DNS) of a laminar premixed Bunsen type flame. DNS results and theory are compared showing very good agreement in terms of both frequency and mode structure. DNS confirms that the frequency of ITA modes does not depend on any acoustic characteristic of the burner. Based on a numerical evaluation of the Flame Transfer Function, stability limits of ITA modes predicted by theory are also recovered in the DNS with reasonable accuracy. Finally, DNS is used to analyze the mechanisms of ITA modes

Causality and intrinsic thermoacoustic instability modes

International audienceDirect numerical simulation of a confined laminar premixed flame has been performed in an anechoic combustor, showing self-sustained intrinsic thermoacoustic oscillations. Theoretical predictions based on acoustic jump relations and the n − τ model for the flame are presented and causality concerns are discussed. The instability’s frequency and mode structure are recovered numerically with very good accuracy. A detailed discussion on the interplay of the physical phenomena responsible for this dynamical coupling is also carried out

Causality and intrinsic thermoacoustic instability modes

Direct numerical simulation of a confined laminar premixed flame has been performed in an anechoic combustor, showing self-sustained intrinsic thermoacoustic oscillations. Theoretical predictions based on acoustic jump relations and the n − τ model for the flame are presented and causality concerns are discussed. The instability’s frequency and mode structure are recovered numerically with very good accuracy. A detailed discussion on the interplay of the physical phenomena responsible for this dynamical coupling is also carried out

Causality and intrinsic thermoacoustic instability modes

International audienceDirect numerical simulation of a confined laminar premixed flame has been performed in an anechoic combustor, showing self-sustained intrinsic thermoacoustic oscillations. Theoretical predictions based on acoustic jump relations and the n − τ model for the flame are presented and causality concerns are discussed. The instability’s frequency and mode structure are recovered numerically with very good accuracy. A detailed discussion on the interplay of the physical phenomena responsible for this dynamical coupling is also carried out