Numerical investigation of flow field effects on fuel–air mixing in a non-reacting trapped vortex combustor with different injection arrangements

Abstract

Large eddy simulation (LES) of turbulent mixing in a trapped vortex combustor (TVC) is carried out using hybrid Eulerian–Lagrangian methodology. The Eulerian filtered compressible transport equations are solved for the resolved velocity and the composition field is provided by the filtered mass density function (FMDF). The reliability of the solver is assessed by investigating a TVC like configuration and the results compare well with the available experimental data. The consistency between Eulerian and Lagrangian parts is statistically quantified proving the performance of the LES/FMDF model. A planar single-cavity TVC is studied in which the fuel and air jets are issued into the cavity from the forebody and the afterbody, respectively. Various injection schemes are considered by changing fuel and air jet locations introducing different vortical structures and mixing qualities. The vortical structure analysis along with various quantitative measures such as mean cavity and near stoichiometric equivalence ratios, global fuel distribution and mixing efficiency curves are invoked to compare fuel/air injection strategies. The primary objective of this study is to identify the arrangement that provides most efficient mixing among the considered arrangements in non-reacting conditions. The predicted results show that configurations with both air and fuel jets adjacent to the mainstream or adjacent to the cavity inferior wall leads to more homogeneous mixture and a better global fuel distribution, with the former configuration performing slightly better. While the latter configuration holds larger local near stoichiometric regions inside the cavity and its interface with mainstream. These results are commensurate with expectations based on the vortical structures analysis and the injected fuel trajectory inside the cavity.