Large eddy simulation/probability density function simulations of the Cambridge turbulent stratified flame series

Abstract

The LES/PDF methodology is applied to the Cambridge/Sandia turbulent stratified flame series. The methane chemistry is represented by the 16-species reduced ARM1 mechanism, and the in situ adap- tive tabulation method is adopted to accelerate the chemistry calculations. Differential diffusion effects are taken into account. The simulations are performed for premixed (SwB1), and moderately and highly stratified (SwB5 and SwB9, respectively) cases under non-swirling conditions. The results from LES/PDF simulations are compared with the experimental measurements and with previous calculations. The cal- culated length of the recirculation zone, the mean and r.m.s. profiles of velocity, temperature, equivalence ratio and mass fractions of species are in very good agreement with the measurements. In the stratified cases, the CO profiles are underestimated within the recirculation zone, close to the bluff body. Scatter plots of species mole fractions and temperature are presented and compared with the experimental data. Conditional means of species mass fractions demonstrate overall good consistency with the measure- ments. A parametric study is then performed to examine the effect of differential diffusion and the effect of the parameter controlling the scalar mixing rate. It is found that differential diffusion has a negligible effect on the mean and r.m.s. results, whereas, the mixing rate parameter has a considerable effect on the flow structure. Finally, the effect of stratification is investigated and characterized by scatter plots of OH mass fraction and heat release rate (HRR) in the equivalence ratio space.