Numerical simulations of Rayleigh-Taylor instability in non-premixed flames using detailed chemistry

The Rayleigh-Taylor (RT) instability occurs at a perturbed interface separating fluids of different densities, when the lighter fluid accelerates the heavier fluid. We examine the occurrence of the RT instability, when the perturbed interface demarcates a light, fuel stream from a heavier air stream at elevated temperatures. The study is conducted using the FLASH code with modifications that include detailed chemistry, temperature-dependent EOS, and diffusive transport. The fuel-air interface is initialized at thermal equilibrium (T$_{\mathrm{fuel}}=$T$_{\mathrm{air}}=$1000K) in a constant background acceleration (g). We vary the density difference across the interface by diluting the H$_{\mathrm{2}}$ fuel stream with inert N$_{\mathrm{2}}$. The non-premixed flame formed across a burning interface alters the underlying density ($\rho )$ stratification, so that an initially RT unstable (stable) interface can be locally stabilized (destabilized). We observe this change in local stability for both single-wavelength and multimode perturbations, and draw some conclusions on the implications of these findings to applications such as ultra-compact combustors. We also make some comparisons of the reacting, non-premixed RT problem with the corresponding inert flow.