Large-Eddy Simulation of Interactions Between a Reacting Jet and Evaporating Droplets |
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Authors: | Jun Xia Kai H Luo Suresh Kumar |
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Institution: | (1) Energy Technology Research Group, School of Engineering Sciences, University of Southampton, Highfield, Southampton, SO17 1BJ, UK;(2) Building Research Establishment Ltd, Garston, Watford, WD25 9XX, UK |
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Abstract: | Large-eddy simulation of a turbulent reactive jet with and without evaporating 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 (St
0) and mass loading ratios (MLR) have been simulated, along with a case without droplets. It is found that compared with the bigger, slow responding droplets
(St
0 = 16), smaller droplets (St
0 = 1) are more efficient in suppressing combustion due to their preferential concentration in the reaction zones. The peak
temperature and intensity of temperature fluctuations are found to be reduced in all the droplet cases, to a varying extent
depending on the droplet properties. Detailed analysis on the contributions of respective terms in a transport equation for
grid-scale kinetic energy (GSKE) shows that the droplet evaporation effect on GSKE is small, while the droplet momentum effect
depends on St
0. When the MLR is sufficiently high, the bigger (St
0 = 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 in the droplet cases than in the pure flame case, due to the
dissipative droplet dynamic effect. |
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Keywords: | LES Interaction Reacting jet Droplets Stokes number Mass loading ratio |
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