  Diffusive transport of mass occurs at small scales in turbulent premixed
flames. As a result, multicomponent mass diffusion, which is often neglected in
direct numerical simulations (DNS) of premixed combustion, has the potential to
impact both turbulence and flame characteristics at small scales. In this
study, we evaluate these impacts by examining enstrophy dynamics and the
internal structure of the flame for lean premixed hydrogen-air combustion,
neglecting secondary Soret and Dufour effects. We performed three-dimensional
DNS of these flames by implementing the Stefan-Maxwell equations in the code
NGA to represent multicomponent mass transport, and we simulated statistically
planar lean premixed hydrogen-air flames using both mixture-averaged and
multicomponent models. The mixture-averaged model underpredicts the peak
enstrophy by up to 13% in the flame front. Comparing the enstrophy budgets of
these flames, the multicomponent simulation yields larger peak magnitudes
compared to the mixture-averaged simulation in the reaction zone, showing
differences of 17% and 14% in the normalized stretching and viscous effects
terms. In the super-adiabatic regions of the flame, the mixture-averaged model
overpredicts the viscous effects by up to 13%. To assess the effect of these
differences on flame structure, we reconstructed the average local internal
structure of the turbulent flame through statistical analysis of the scalar
gradient field. Based on this analysis, we show that large differences in
viscous effects contribute to significant differences in the average local
flame structure between the two models.
