Large-eddy simulation of interactions between a reacting jet and evaporating droplets

Large-eddy simulation of a turbulent reactive jet with evaporating liquid droplets is performed to investigate the interactions among turbulence, combustion, heat transfer and evaporation. A hybrid Eulerian-Lagrangian approach is used for the gas-liquid flow system. Arrhenius-type finite-rate chemistry is employed for the chemical reaction. To capture the highly local interactions, dynamic procedures are used for all the subgrid-scale models, except that the filtered reaction rate is modelled by a scale similarity model. Various representative cases with different initial droplet sizes (St0) and mass loading ratios (MLR) have been simulated, along with a reacting case without droplets. It is found that compared with the bigger, slow responding droplets (St0=16), smaller droplets (St0=1) are more efficient in suppressing combustion due to their preferential concentration in the reaction zones. The peak temperature and intensity of temperature fluctuation are found to be reduced in all the droplet cases, to a varying extent depending on the droplet properties. From the budget analysis of grid-scale kinetic energy (GSKE), it was found that the droplet evaporation effect on GSKE is small, while the droplet momentum effect greatly depends on St0. When the MLR is sufficiently high, the bigger (St0=16) droplets can have profound influence on GSKE, and consequently on the formation and evolution of large-scale flow structures. On the other hand, the turbulence level is found to be lower for the droplet cases than for the flame case, due to the dissipative droplet dynamic effect, which is overwhelming against the decreased molecular viscosity effect