Chain snapping in Newtonian and viscoelastic fluids

It is known that particles sedimenting in a viscoelastic fluid form chains. It has been observed in experiments and in numerical simulations that the last particle in the chain gets detached from the chain (chain snapping). In this paper the mechanism for the chain snapping was investigated. We found that this phenomenon is not peculiar to viscoelastic fluids. Similar chain snapping can be observed in Newtonian fluids under certain ideal conditions. A long chain of particles tends to fall faster than a single particle. This causes the separation of the last particle from the chain. In Newtonian fluids, detachment will not occur if the inertial wake effects are strong enough to cause substantial drag reduction on the last particle. In a viscoelastic fluid the detachment is also restricted by the normal stress due to the elastic effects of the fluid.