Direct numerical simulation of evaporating droplets

A model for the three-dimensional direct numerical simulation of evaporating, deforming droplets in incompressible flow is presented. It is based on the volume-of-fluid method and is therefore capable of capturing very strong deformations. The evaporation rate is computed based on the vapour mass fraction and the PLIC reconstruction of the surface. Emphasis is put on the correct calculation of the velocities of the gaseous and liquid phase at the interface which is very important for cases with high mass transfer rates and thus high Stefan flow. It is accomplished by the use of an iterative algorithm that enforces a divergence constraint in cells containing the interface.Validation comprises a 1D test case for interfacial mass transfer, droplet collisions and oscillations as well as calculation of Sherwood numbers for two different cases of evaporating droplets where low and high mass transfer rates occur. Comparison with data from the literature shows good agreement of the obtained results.The simulation of a strongly deformed water droplet in a flow at a high Reynolds and Weber number is used to demonstrate the capabilities of the presented method. The emerging flow field in the wake of the droplet is very complex and three-dimensional.