Droplet interactions during combustion of unsupported droplet clusters in microgravity: Numerical study of droplet interactions at low Reynolds number

The present work developed a numerical model to study the combustion of well-characterized drop clusters in microgravity environment using direct numerical simulation by the means of Fire Dynamic Simulator---a CFD model of fire-driven fluid flow. The computational research investigated the combustion of clusters of droplets of different sized and asymmetric three-dimensional configurations in zero gravity environments for zero relative Reynolds numbers. One of the aspects studied is droplet interaction during evaporation and combustion over the lifetime of the droplet. The model developed accounts for variable gas-phase thermophysical properties, unity Lewis number, Stefan velocities and includes the gas-phase radiative transfer (solved by a finite volume method) for finite rate reaction. Mass burning rates are calculated for each droplet in an array and compared to mass burning rate of similar single droplet, the ratio of these two being a correction factor eta. Single droplet combustion has been studied to evaluate and validate the model output. It was found that single droplet combustion does follow the d2-law, mass burning rates being in excellent qualitative agreement with current theories and experimental data. Direct numerical results of multiple droplet combustion were obtained and compared with a point source method as well as with experimental and numerical models developed in the past. Data obtained with proposed method provided results consistent with and in qualitative agreement with multiple droplets combustion theories and experimental investigations. Quantitatively, the numerical model results were in the range of 85% to 95% of the results provided by the investigations found in the literature for droplet array combustion models and in the range of 85% to 90% when compared with single droplet combustion models.; The numerical simulation along with the future proposed experiment described in the project is a unique combination of investigative methods that will provide support for future investigations and for understanding of droplet interaction phenomena.