Scalar mixing in direct numerical simulations of temporally evolving plane jet flames with skeletal CO/H₂ kinetics

Direct numerical simulations of three-dimensional turbulent temporally evolving plane CO/H₂ jet flames are performed with detailed chemistry at Reynolds numbers of up to 9000 and with up to 500 million grid points. The effect of Reynolds number on turbulent mixing properties and flame structure is quantified for low Damköhler number flames. These flames exhibit strong flame-turbulence interactions resulting in local extinction followed by re-ignition. The probability density of the stoichiometric scalar dissipation rate is found to be nearly log-normal with some negative skewness. Conditional statistics of the hydroxyl radical reveal increasing levels of extinction and longer re-ignition times with increasing Reynolds number. The mechanical-to-scalar mixing time scale ratio, a key quantity in transported probability density function (pdf) modeling, is investigated for both conserved and reacting scalars. The conserved scalar timescale ratio is found to be consistent with prior studies. For reacting scalars, the effects of molecular diffusivity and chemical reaction on the timescale ratio are quantified.