Dynamics of differential diffusion effects in turbulent premixed hydrogen flames at varying Karlovitz number

At low Karlovitz number, thin, turbulent flames are dominated by molecular transport so differential diffusion effects are significant. However, as the Karlovitz number increases, turbulent transport eventually overwhelms the molecular transport such that the differential diffusion effects are diminished. In this work, both global and local differential diffusion effects in turbulent premixed flames are investigated. To evaluate the impact of these effects under different turbulence conditions, detailed simulations have been conducted for turbulent hydrogen flames at varying Karlovitz numbers. Instantaneous profiles of species mass fraction in progress variable space were extracted and used to compute element mass fractions whose variation with respect to progress variable is indicative of differential diffusion. These results identify overall trends in differential diffusion with increasing Karlovitz number and indicate that the magnitude of differential diffusion effects fluctuates locally and depends on the local turbulence conditions. Finally, a manifold-based combustion model is evaluated taking into consideration the non-unity Lewis numbers.