Hybrid Rans/PDF calculations of a swirling bluff body flame (Sydney 'SM1')

In this work, we perform steady 2D axisymmetric RANS and hybrid RANS/PDF calculations to predict the turbulent flow and mixing fields of a swirling bluff body flame (Syndey SM1). The case studied, SM1, is a bluff body stabilized flame, studied experimentally at Sydney University and Sandia National Laboratories. Turbulence is modeled with a nonlinear k-ε type model, taking into account effects of rotation and streamline curvature on the turbulence. Flow field predictions are in reasonable agreement with experimental data. However, the agreement for mean mixture fraction and mixture fraction variance with experimental results is less satisfactory. Yet, the mean temperature field is quite well reproduced. We first compare presumed and transported scalar PDF simulation results, with the same laminar flamelet model for chemistry. The influence of the micro-mixing model is small in this case. The mixing model constant Cφ has a stronger influence, through the mixture fraction variance. Finite rate chemistry effects are studied in transported scalar PDF calculations using REDIM. For Cφ = 2, a steady solution is obtained with EMST, but with CD the flame extinguishes. The combination REDIM/EMST is not able to predict the local extinction seen in the experiments. Therefore, a final calculation with the CD model with Cφ=3 is performed and a steady solution is found. With CD, there is more scatter than with EMST, resulting in lower values for temperature and Y(CO2). Still, this combination REDIM/CD is not able to predict the correct level of local extinction, though