Published online by Cambridge University Press: 21 July 2021
Dynamic and stationary axisymmetric deformation of viscous toroidal drops submerged in slow viscous flow are studied numerically. The immiscible ambient fluid is subject to a combination of rotation and extensional/compressional (biextensional) flow. The creeping flow approximation is assumed. The numerical simulations are performed with the help of the boundary integral method. The process under consideration is governed by three dimensionless parameters: the capillary number that characterizes the ratio of viscous and surface tension forces; the Bond number, that characterizes the ratio of centrifugal and surface tension forces; and the ratio of viscosity of the two fluids. Our simulations for the equal viscosity case demonstrated that, depending on the governing parameters, the toroidal drop either collapses, extends indefinitely or it attains a stationary toroidal shape. The latter may be stable or unstable with respect to axisymmetric disturbances. Conditions for the realization of each of the dynamic regimes and stationary states in terms of governing parameters are presented. In particular, stable toroidal shapes result under the combined action of rotation and extensional flow, and were not found under the action of rotation and compressional flow.