Towards Large Eddy Simulations of a Bluff Body Burner Using an Unstructured Grid

A Large Eddy Simulation of a bluff body flame has been carried out using an unstructured grid. The flame, burning a methane-hydrogen fuel with detailed combustion chemistry (based on a mechanism of 18 species) is simulated using STAR-CD. The mixture fraction is used as a conserved scalar, and a subsequently temperature, density and species mass fraction are calculated using a probability density function. A beta function presumed-PDF (PPDF) has been used. The beta function is parameterized by the filtered mixture fraction and mixture fraction variance. The Scalar dissipation is modeled by assuming proportionality between the sub grid mixing time scale and turbulent time scale. Due to the large domain size, the adequate resolution of the reacting part of the flow presents a challenge. To address this difficulty, we have exploited embedded mesh refinement in and around the reaction zone. The velocity profiles are in good agreement near the jet inlet but are slightly over predicted at the center line, far from the jet inlet. The model has under predicted the temperature at the start of the flame. The selection of a correct coefficient for the scalar dissipation is identified as the source of the under prediction.