| Turbulent spray combustions are encountered in a variety of engineering applications, such as aircraft engines and automobile engines. The evaporation of liquid fuel plays an extremely important role in the process of combustion. Essentially, the combustion of liquid fuel is diffusion combustion, in which the rate of combustion is larger than that of evaporation, so the droplets evaporation rate greatly influences the combustion rate of liquid fuels. Thus, the research on turbulent spray evaporation is of significant value.Based on the Large Eddy Simulation (LES), the Probability Density Function (PDF) method was introduced to derive the transport equation of the fluid velocity seen by the particles, and then an LES/FDF (Filtered Density Function) model was developed for two-phase flow. The droplets evaporation was simulated with an infinite conductivity evaporation model, and the effect of convection on mass and heat transfer was taken into consideration. A set of numerical models was established and a computer program was developed to numerically investigate the turbulent spray evaporation.An evaporating spray in a model combustor with an expansion ratio of3was simulated. Mean and RMS properties of the gas phase and droplets were obtained and compared with experimental data, such as velocity, temperature and diameter. It was shown that the LES can well predict the time-averaged and fluctuating velocity of gas phase, and the FDF model can well describe the droplets dispersion in two phase flow. The droplets evaporation model used in this study could accurately predict the transport process of mass and temperature between gas phase and liquid phase.The droplets spray evaporation was closely related to the environment, the influence of environmental temperature and ambient pressure on spray evaporation was analyzed. The numerical results showed that high environmental temperature can improve the rate of evaporation, while high ambient pressure would decrease the rate of evaporation. |
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