A buckling mechanism for confined suspension flows: Rheology and dynamics
The rheology of confined flowing suspensions, such as blood, depends upon the dynamics of the components, which can be particularly rich when they are elastic capsules. Using spectral boundary integral methods, we simulated a two-dimensional model channel through which flows a dense suspension of fluid-filled capsules. A parameter of principal interest is the equilibrium membrane perimeter, which ranges from round capsules to capsules with a dog-bone-like equilibrium shape. We showed that the minimum effective viscosity occurs for a biconcave equilibrium shape, similar to a red blood cell. The rheological behavior changes significantly over this range; transitions are linked to specific changes in the capsule dynamics. Most noteworthy was an abrupt change in behavior when the capsule at-rest shape is sufficiently slender, correlating with the onset of capsule buckling. Buckled capsules have a more varied orientation and make significant rotational (rotlet) contributions to the capsule–capsule interactions.
S. H. Bryngelson and J. B. Freund, “Buckling and its eﬀect on the conﬁned ﬂow of a model capsule suspension,” Rheol. Acta 55, 451-464 (2016)