Interactions of Turbulence and Thermodiffusive Instabilities in Premixed Lean Hydrogen Flames*

A series of large-scale Direct Numerical Simulations (DNS) of turbulent lean, premixed hydrogen flames susceptible to thermodiffusive instabilities has been performed in a slot burner configuration at a jet Reynolds number of 11,000 using finite rate chemistry. The DNS comprise a variation of the flames’ Karlovitz number while the Reynolds number is kept constant to allow for a variation of flame/turbulence interactions. Since thermodiffusive instabilities result from the significantly different diffusivity of the hydrogen molecule with respect to the other species, additional DNS, where diffusivities of all species are set to the thermal diffusivity (unity Lewis number assumption), are conducted. For the flames considering realistic diffusivities, which are particularly important for hydrogen, the profiles of heat release and temperature show the characteristic behavior of thermodiffusive instabilities, e.g. local flame extinction and temperature overshoots in the burned gas, which are not existent in the unity Lewis number flames. The effects of the Karlovitz number on the thermodynamic state within the flame are discussed and the DNS are compared to two-dimensional flames in a laminar flow that feature thermodiffusive instabilities and have been performed in previous work.