Numerical simulations of non-premixed Rayleigh-Taylor flames

Using detailed 3D numerical simulations of a non-premixed, Rayleigh-Taylor (RT) flame, we have identified new mechanisms for stabilization and destabilization of the underlying flow¹. The flow is initialized with a sharp interface separating the fuel and oxidizer streams, that supports multimode perturbations. The simulations were performed using the astrophysical FLASH code, with appropriate modifications² to support accurate computations of chemically reacting flows with heat release. In particular, molecular transport of mass, momentum and heat are implemented through a newly developed, flux-based solver compatible with Adaptive Mesh Refinement for efficient computations. The Atwood number driving the instability growth is varied by changing the concentration of Nitrogen in both the fuel and oxidizer streams. The flame is initiated by auto-ignition of a combustible mixture produced initially by physical diffusion and later sustained by the mixing process associated with the RT instability. The problem setup is of relevance to several applications including ultra-compact combustors (UCC) which experience high-g loading of magnitude ~ 10⁴g₀ across the fuel-air interface, which could be susceptible to RT mixing.

¹N. Attal, P. Ramaprabhu, Physica D, 404, 132353, (2020)

²N. Attal, P. Ramaprabhu et al., Comp. & Fluids, 107, 59-76, (2015)