Abstract

Simulations for the Cambridge swirl bluff-body spray burner are performed near blow-out conditions. The sensitivity of the results to the subgrid mixture fraction and progress variable variances is studied. Hybrid stress blended eddy simulations (SBES) are used for sub-grid turbulence closure. SBES blends the RANS SST model at the boundary layer with large eddy simulation Smagorinsky model away from the wall. N-heptane spray droplets are tracked using a typical Eulerian-Lagrangian approach. Chemistry and mixing are closed using the Flamelet Generated Manifold (FGM) model. Coupled heat transfer between the walls and the near-wall fluid are accounted for at the bluff-body surface. Good results are shown matching the spray SMD and axial velocity. The study focuses on studying the impact of modeling the mean mixture fraction and progress variable variances on spray vaporization in the context of the FGM and flamelet models. Algebraic models versus transport models are also compared to assess the difference on the results.  The results show that the impact is mostly at the onset of the ignition kernel where mixture fraction variance can be high.  The progress variable variance source term was found to have a lesser impact on the results.  Future work will focus on investigating more realistic stable simualiton conditions.