ONE-DIMENSIONAL SIMULATIONS OF FREELY PROPAGATING TURBULENT PREMIXED FLAMES

The propagation rate and the structure of freely propagating premixed turbulent flames are investigated using a one-dimensional simulation m odel based on a new version of the linear-eddy model (LEM) of Kerstein (1991, 1992). This model explicitly includes thermo-diffusive, finite -rate kinetic, and heat release effects. Reasonably good quantitative agreement in predictions of turbulent flame speed with fan-stirred bom b experiments of Abdel-Gayed et al. (1984a) is obtained over most of t he reported u'/S-L range. LEM predicts a rapid increase in u(t)/S-L wi th u'/S-L for low u' followed by a bending slope of u(t)/S-L with incr easing u' that was also observed in the experiments. Here. u(t) and S- L are, respectively, the turbulent and stretch free planar laminar fla me speeds and u' is the r.m.s, turbulence intensity. Comparisons with an earlier model based on the G-equation (Menon and Kerstein, 1992) fo r flamelet combustion are also made. The resulting propagation speeds are also in good agreement. Comparisons with weak-swirl burner experim ents of stationary flames by Bedat and Cheng (1995) show that the mode l underpredicts the reported u(t)/S-L with u'/S-L. However, progress v ariable probability density functions at different locations within th e flame reveal the onset of distributed combustion which is predicted by the location of the flame on the Borghi combustion phase diagram (B edat and Cheng, 1995). Finally, constant Reynolds number simulations f or a range in S-L/u' compare well with experiments by Abdel-Gayed er a l. (1979) for low u', but predict a plateau in u(t)/S-L as u increases , and decreasing u(t)/S-L with further decrease in S-L/u'. This behavi or is interpreted as correct based on physical arguments.