A combined experimental and computational fluid dynamics analysis of the dynamics of drop formation

This article presents a complementary experimental and computational investigation of the effect of viscosity and flowrate on the dynamics of drop formation in the dripping mode. In contrast to previous studies, numerical simulations are performed with two popular commercial computational fluid dynamics (CFD) packages, CFX and FLOW-3D, both of which employ the volume of fluid (VOF) method. Comparison with previously published experimental and computational data and new experimental results reported here highlight the capabilities and limitations of the aforementioned packages. Results at high flowrates and higher viscosity show that the singlephase simulation technique (FLOW-3D) offers significant efficiency gains' when compared with a multi-phase approach (CFX). Furthermore, comparison with experimental results reveals that for the same grid resolution, the single and multiphase solvers offer similar accuracy of prediction and both are able to capture the features of greatest practical engineering interest, such as primary drop volume as a function of flowrate. For low flowrates and viscosity, for example, which exhibit fine interfacial features such as thin liquid threads and the existence of satellite drops, the CFD predictions are found, in general, to be poorer with the issue of free surface smearing introduced by the VOF method and surface tension becoming dominant. In such cases, neither of the commercial packages is found to offer wholly reliable engineering design data.