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 model 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 heal release effects. Reasonably good quantitative agreement in predictions of turbulent flame speed with fan-stirred bomb experiments of Abdel-Gayed el at. (1984a) is obtained over most of the reported u’/SL range. LEM predicts a rapid increase in ut/SL with u’/SL for low u’ followed by a bendiny slope of ut/SL with increasing u’ that was also observed in the experiments. Here, ut and SL are, respectively, the turbulent and stretch free planar laminar flame speeds and u’ is the r.m.s. turbulence intensity. Comparisons with an earlier model based on the G-equation (Menon and Kerstein, 1992) for flamelet combustion are also made. The resulting propagation speeds are also in good agreement. Comparisons with weak-swirl burner experiments of stationary flames by Bedat and Cheng (1995) show that the model under-predicts the reported ut/SL with u’/SL. However, progress variable probability density functions at different locations within the flame reveal the onset of distributed combustion which is predicted by the location of the flame on the Borghi combustion phase diagram (Bedat and Cheng, 1995). Finally, constant Reynolds number simulations for a range in SL/u’ compare well with experiments by Abdel-Gayed et al. (1979) for low u’, but predict a plateau in uJSL as u’ increases, and decreasing utSL with further decrease in St/u’. This behavior is interpreted as correct based on physical arguments.