Deformation of a Droplet Passing Through a Contraction

Deformation of a droplet passing through a contraction and expansion at intermediate to large Reynolds number is predicted numerically and compared with experimental observations. The effects of fluid properties, contraction geometry and flow behaviour is considered. The experiments were performed for silicon oil droplets in water moving through a contraction. Orifice and droplet diameter were of the order of millimetres. Contraction length and flow rate were varied, while the contraction ratio was kept constant (1:4). The droplets are stretched by the contraction, after which oscillations are observed on the interface. Observation of the systems indicated that a disintegration zone exists for droplets above a critical size. Numerical simulations were carried out using an axisymmetric Volume-of-Fluid (VOF) code. Simulations were carried out to match the experimental conditions as well as for a few different Reynolds and Weber numbers. Results showed qualitative agreement with experiments. The predictions indicate that vortices within the contraction are responsible for the capillary-like waves on the stretched droplet.