The objective of the proposed numerical study is to enhance the understanding of liquid droplet vaporization and mixing processes in a turbulent flow. The numerical study employs direct numerical simulations (DNS) to examine the two-way interactions between freely-moving vaporizing droplets and isotropic turbulence. The droplets will be fully resolved in 3D space and time, i.e. not treated as point particles, and all the scales of the turbulent motion are resolved down to the smallest relevant length- and time-scales (the Kolmogorov scales). The emphasis will be on the two-way exchange of mass, momentum and energy between the vaporizing droplets and the surrounding turbulent gas. The turbulence will be assumed isotropic as a first step before considering turbulent shear flows in future studies.
The proposed DNS study will be the first that fully resolves the flow inside and outside a large number of freely-moving vaporizing droplets in a turbulent flow. The detailed results of the proposed DNS, with two-way coupling between the droplets and turbulence, can be used to develop and verify the mathematical models for the subgrid scales of large eddy simulations (LES) as well as Reynolds-averaged models. It should be emphasized that the detailed DNS data which will be obtained from the proposed research are not available in any published experimental or numerical study (Birouk & Gokalp, 2006).
The experimental study which is being currently performed in parallel with the DNS study will examine the effects of turbulence on the vaporization rate of a single droplet moving freely in isotropic turbulence. In addition to enhancing the understanding of the physics of interaction between turbulence and vaporization, the measurements will be used to validate our DNS methodology since no other comparable experimental data exist for free-flying droplet evaporation in isotropic turbulence where the Kolmogorov length scale of turbulence is smaller than the initial droplet size. Hence, the coupled experiment and computations will determine the key interactions between evaporation and turbulence.
The results of the proposed study will have a significant impact on the efficient utilization of energy. This impact stems from the fact that the vaporization rate is the main controlling mechanism of fuel droplet combustion and that liquid fuels are the most important source of energy for all modes of transportation and will remain as such for the foreseeable future. Understanding the physical details of the vaporization and mixing processes in a turbulent flow is an essential prerequisite to understanding the chemical reaction process and the eventual control/optimization of the energy conversion process. The PI has a record of accomplishment in the field of study and in combining research and teaching.
