A numerical study of diffusive effects in turbulent lean premixed hydrogen flames

Three-dimensional direct numerical simulation of lean premixed hydrogen flames is used to explore the influence of species and thermal diffusion and viscosity on the flame structure and turbulent flame response. The leading-order flame response is shown to be due to the global Lewis number with little influence from the other species. The previously-reported observation of decorrelation of fuel consumption and heat release at high Karlovitz numbers is shown to be solely due to atomic hydrogen diffusion. Finally, it is shown that the suppression of turbulence through the flame cannot be attributed to an increase in viscosity due to the increase in temperature, but that the effect is not negligible. It is further argued that turbulence–flame interactions are better described considering Kolmogorov’s second similarity hypothesis (rather than the first); specifically, by a Karlovitz number that is defined based on the inertial subrange (i.e. the energy dissipation rate) rather than the dissipation subrange (i.e. viscosity or equivalently Kolmogorov scale quantities)