A high-fidelity two-phase large eddy simulation (LES)/filtered mass density function (FMDF) model is developed and used for detailed simulations of turbulent spray breakup, evaporation and combustion. The spray is simulated with Lagrangian droplet transport, stochastic breakup, wake, collision/coalescence and finite rate heat and mass transfer submodels. The spray/droplet model is used together with a compressible LES gas flow model for numerical simulations of high pressure liquid jets sprayed into a high temperature and pressure gas chamber. Various non-evaporating and evaporating sprays at different ambient gas pressures and temperatures (all without reaction) are simulated. The numerical results are compared with the available experimental data for global spray variables such as the spray penetration length and droplet Sauter mean diameter (SMD). In all cases, the gas velocity and turbulence generated by the spray are found to be very significant. A broad spectrum of droplet sizes is also generated by the complex and coupled effects of the gas flow turbulence, droplet breakup and evaporation. Droplet-wake interactions are shown to play an important role in the spray evolution. The effect of subgrid turbulence model on the global spray features, like the spray penetration, is also very significant at lower gas temperatures. The interaction of the induced gas flow turbulence with the spray is studied at different chamber densities and temperatures as well as different nozzle sizes and injection pressures. It is indicated that the local rate of evaporation and its interaction with the gas density field are the key factors that control the induced gas turbulence and its interaction with the spray. It is shown that spray with a larger nozzle induces higher turbulence due to increase in local evaporation rate of small droplets by the higher entrained gas. Our results also indicate that spray penetration remains unchanged with variation in injection pressure due to competing factors of evaporation and vapour convection. The developed spray LES model is coupled with the two-phase FMDF model for simulation of high speed spray combustion. The FMDF is a subgrid-scale probability density function (PDF) model for LES of turbulent reacting flows and is obtained by the solution of a set of stochastic differential equations by a Lagrangian Monte Carlo method. Complex skeletal kinetics models are used for the chemical reaction together with in situ adaptive tabulation (ISAT) and chemistry workload balancing for efficient parallel computations. Simulations of evaporating sprays with and without combustion indicate that the two-phase LES/FMDF results are consistent and compare well with the available experimental data for the ignition delay time and flame liftoff lengths at different ambient gas temperatures and oxygen concentrations. It is shown that for low to moderately high ambient gas temperatures, the auto-ignition occurs at the tip of spray vapour jet where there is considerable spray-induced gas turbulence and fuel-air mixing. The LES/FMDF results for ignition delay show more sensitivity to the chemical kinetics model at lower gas temperatures due to slower reaction and stronger turbulence-chemistry interactions. The liftoff length is less sensitive to the kinetics. The spray controlled flame tends to move away from a diffusion flame structure toward a premixed one as the oxygen concentration decreases and/or the ambient gas temperature increases because of changes in spray-induced turbulence and mixing. A moderately dense droplet laden planar jet is also simulated by the LES/FMDF model for detailed study of the liquid volume fraction effects. It is indicated that the neglect of liquid volume fraction will lead to excessive evaporation and turbulence modulation. On the other hand, the volume displaced by the dispersed droplets increases the entrained gas to the droplet laden jet. It is shown that for LES/FMDF model to be consistent and accurate, it is necessary to include the volume fraction into the FMDF equation.
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