Rayleigh-Taylor Unstable Flames: the Coupled Effect of Multiple Perturbations

In this talk, we explore the effect of the Rayleigh-Taylor instability on premixed flames. Using 2D direct numerical simulations (DNS) of Boussinesq flames with a model reaction rate, we show what happens when the flame is influenced by three types of perturbation: a large amplitude single-mode primary perturbation, a smaller amplitude single-mode secondary perturbation, and a multimode numerically-generated system perturbation. Early on, the evolution of the flame is dominated by the primary perturbation and the flame propagates as a metastable traveling wave in the form of bubbles separated by cusp-like spikes. However, the lifetime of this traveling wave depends on the properties of the secondary and system perturbations and on the strength of gravity. Once the traveling wave is destabilized, the bubbles rapidly grow to large scales. The level of organization of this process depends on the balance and interactions between the three types of perturbation. Finally, we compare this growth process to the growth of the mixing layer in non-reacting Rayleigh-Taylor.