Direct comparison of PDF and scalar dissipation rates between LEM simulations and experiments for turbulent, premixed methane air flames

Abstract

We present a direct comparison between the predicted and measured probability density functions (PDF) of the reaction progress variable and conditioned values of the scalar dissipation rates (SDR) in premixed turbulent flames. The predictions are based on simulations of premixed flames using the linear-eddy model (LEM), parameterised by a wide range of integral length scales and turbulent Reynolds numbers. The experimental results are highly spatially resolved temperature and species data from the Cambridge-Sandia swirl burner. The LEM simulations display remarkable accuracy in capturing the features observed experimentally. Further, the results reveal that the LEM calculated PDF and SDR for premixed flames remain relatively steady under a variety of turbulent conditions, including variations in the integral length and turbulent Reynolds number. In general, it appears to be practical to use representative pseudo-turbulent PDF and SDR models for a range of turbulence intensities and length scales.

A LES-CMC formulation for premixed flames including differential diffusion

“…f (z ) is the functional dependence on the conditioning variable estimated a priori using laminar flames simulated by PREMIX [68]. This is justified by the weak dependence of f (z ) on strain rate, especially in the reactive-diffusive layer of the flame [67], and on measurements in low swirl flows [69]. The unconditional scalar dissipation rate, , is evaluated at the LES resolution as , where is the SGS contribution addressed later.…”