PREDICTION OF EVAPORATING SPRAY IN ANISOTROPICALLY TURBULENT GAS FLOW

Abstract

Numerical investigation was conducted for a confined evaporating isopropyl alcohol spray issuing into a coflowing, heated turbulent air stream. The Eulerian-Lagrangian stochastic model was used for the spray calculations. The gas phase turbulence was modeled using either the isotropic eddy viscosity model or the second-moment transport model for both Reynolds stresses and heat fluxes. Two droplet dispersion models were studied for the Lagrangian trajectory calculations; the conventional particle-eddy encounter model and the time-correlated dispersion model. In the time-correlated model, gas phase turbulent velocity fluctuations were correlated temporally and directionally between two successive time steps in modeling the droplet dispersion. The droplet evaporation was accounted for by the infinite-conduction evaporation model, where the gas-film variable properties were considered using the one-third rule. Detailed numerical results of the liquid droplet phase, i.e., the droplet mean diameters, mass fluxes, mean, and fluctuating velocities were presented and discussed by comparison with the experimental data. Results show that the droplet mean properties are generally not sensitive to the gas phase turbulence models and the droplet dispersion models, ail of which can give agreeable predictions with the measurements except for the droplet mass fluxes, which accumulate persistently near the centerline far downstream in all calculations. It is found that the conventional particle-eddy encounter model fails to account for the anisotropy of droplet turbulence, no matter what turbulence model is used for the gas phase. The anisotropy of droplet phase turbulence, however, is well predicted by the time-correlated dispersion model in conjunction with the gas phase second-moment transport model.