Experimental-Numerical Comparison of Premixed Turbulent Flame Kernels in Expanding Supersonic Channel Flow

It was recently shown using experiments that premixed supersonic flame kernels exposed to a mean acceleration develop a vortex ring motion due to baroclinic torque (Ochs et al., FTC 2018, https://doi.org/10.1007/s10494-018-9947-x). One major conclusion is that, when compared to well established low-speed spherical flame studies, the growth of supersonic kernels is enhanced due to the vortex ring motion. However, the previous work utilized a line of sight Schlieren measurement to assess flame growth and it is unclear to what extent the observations would change if the full three-dimensional flame topology was available. In order to answer this question, extensive Large Eddy Simulations of supersonic premixed flame kernels are performed. Numerical validation is demonstrated by comparing the experimental flame speed to a numerical flame speed calculated using numerical Schlieren and processed in a similar fashion to the previous experimental data. Reasonable agreement is found across all cases. It is shown that the vortex ring motion has a non-negligible effect on the late time flame topology, which has important implications on turbulent flame speed scaling in supersonic expanding flows.