Direct numerical simulations of evaporating droplet dispersion in forced low Mach number turbulence

Dispersion of evaporating droplets in forced low Mach number isotropic turbulence is studied using direct numerical simulation (DNS). The carrier phase is treated in the Eulerian frame, the droplets are tracked in the Lagrangian frame, and a (realistic) two-way coupling is considered. The results of the simulations are used to investigate the effects of the initial droplet time constant, the initial mass loading ratio, the initial droplet temperature, the latent heat of evaporation, the boiling temperature, and the initial vapor mass fraction on the droplet size, the temperature fields, and the vapor mass fraction. The DNS results indicate that the evaporation rate is nonlinear during the early times. The pdfs of the droplet diameter are skewed towards smaller droplets, however, they may be approximated as Gaussian for small mass loading ratios. An examination of the mean vapor mass fraction indicates that the mixture becomes nearly saturated at long times. The evolution of the fluctuating vapor mass fraction is investigated by considering the transport equation for the variance of this quantity. (C) 1998 Elsevier Science Ltd. All rights. reserved.