Intrinsic Flame Instabilities in Turbulent Premixed Hydrogen Flames: A DNS Study

Large-scale Direct Numerical Simulations (DNS) of turbulent, lean, premixed hydrogen flames susceptible to intrinsic thermodiffusive instabilities have been performed in a slot burner configuration at a jet Reynolds number of 11,000 using finite rate chemistry. A variation of the flames' Karlovitz number is considered while the Reynolds number is kept constant to investigate different regimes of flame/turbulence interaction. Additionally, DNS with identical thermal and species diffusivities (unity Lewis number assumption) are conducted to suppress thermodiffusive instabilities and rigorously assess their effects. The turbulent flames clearly show the typical features of thermodiffusive instabilities such as super-adiabatic temperatures, local extinction, and a significant enhancement of the flame speed. The interactions of thermodiffusive instabilities and turbulence significantly affect the mechanisms of flame surface area generation and the local chemical state in the flame. Turbulent flame wrinkling shows a synergistic effect on thermodiffusive instabilities as large curvature values further enhance the effects of differential diffusion. Finally, conditions of future DNS to further explore the interactions of thermodiffusive instabilities and turbulence are discussed.