Interaction of a Gaussian acoustic wave with a turbulent non-premixed flame

Abstract

A Direct Numerical Simulation (DNS) of a turbulent non-premixed flame interacting with a Gaussian acoustic wave is carried out in this work. This numerical simulation takes into account detailed transport phenomena including the Soret effect as well as complete chemical kinetics on a very fine mesh. Turbulent non-premixed flame calculations are carried out both with and without an acoustic wave and results are recorded at the same time. By a simple difference it is then possible to obtain the influence of the acoustic wave/turbulent flame interaction. Using an extension of the non-linear Rayleigh criterion to a system with many species and elementary reactions, the obtained results can be further analysed. The initially planar acoustic wave develops strong perturbations along its transverse direction because of the interaction process, even at very early times. The amplitude of the pressure perturbation presents locally high positive as well as negative values, demonstrating the importance of focussing/defocussing effects and local amplification (resp. damping) phenomena. In the same way, the heat release rate is locally modified (either increased or decreased) during the interaction process. Finally, the presented Rayleigh criterion is used to identify regions where local amplification (respectively damping) takes place. Both amplification and damping zones coexist directly close to each other inside the reaction zone. The observed, resulting global effect is thus based on an average over highly varying local conditions within the flame front, leading to a smoothing effect. The complexity of the coupling procedure leading to this global wave amplification or damping is demonstrated by the present analysis.

Keywords:

• Combustion instabilities
• DNS
• Non-premixed turbulent flame
• Rayleigh's criterion
• Wave scattering

Acknowledgments

This work has received financial support of ONERA in a project monitored by Dr. Billet. Fruitful discussions with Drs. Giovangigli, Bendahkhlia and Mareschal de Charentenay as well as with M.Sc. Shalaby are appreciated.