Numerical study of double emulsions flowing through a tapered nozzle in axi-symmetric Stokes flow.

A boundary integral method is applied to simulate the motion of double emulsions through a tapered nozzle in axi-symmetric Stokes flow. Double emulsions are a mode of choice to encapsulate and release active materials in applications such as drug delivery, food processing and cosmetics.  Motivated by experiments of Chen et al (Softmatter 2011, vol 7, no 6, 2345) we simulate the motion of two drops, one within the other, carrying distinct fluids, as they exit
an axi-symmetric tapered nozzle. First, we present the approach taken to accurately evaluate the relevant boundary integrals. In particular, difficulties leading to (1) loss of accuracy in the induced fluid velocity near, but not on, an interface, and (2) loss of accuracy near the nozzle exit, are addressed. We then present results for a range of nozzle angles and fluid densities.