Flow of Suspensions

This working area addresses mainly the behaviour of single drops and pairs of trailing drops made from dilute suspensions of tiny particles, undergoing gravitational sedimentation with negligible effects of inertia and interfacial tension. These conditions correspond to a low Reynolds number and an infinite Bond number. The phenomena observed for a gravitationally driven motion of drops made of homogeneous liquids or suspensions are fundamental to the mechanics of multiphase flows, and have applications in many chemical and pharmaceutical processes. Similar effects occur in geophysical flows. Thus, the but very basic problem of sedimenting drops has motivated a considerable body of experimental and theoretical work. The key stages of deformation of single drops and pairs of interacting drops are identified. Of particular interest are the coalescence of two trailing drops, the subsequent formation of a torus, and the break-up of the torus into two or more droplets in a repeating cascade. To track highly deformed interfaces and coalescing and dividing drops, we developed a formal analogy between drops of homogeneous liquid and a dilute, uniformly distributed swarm of sedimenting particles. Numerical simulations using only swarms of Stokeslets reproduce the main phenomena observed in the classical experiments and in our visualization studies. Detailed particle image velocimetry (PIV) enable a mechanistic analysis and confirm the theoretical results.