TitleDynamics and rheology of a dilute suspension of elastic capsules
NameKalluri, Ram Chandra Murthy (author), Bagchi, Prosenjit (chair), Shan, Jerry (internal member), Shapley, Nina (outside member), Rutgers University, Graduate School - New Brunswick,
SubjectMechanical and Aerospace Engineering,
DescriptionThree-dimensional numerical simulations using front-tracking method are considered to study the dynamics and rheology of a suspension of elastic capsules in linear shear flow over a broad range of viscosity contrast (ratio of internalto- external fluid viscosity), shear rate (or, capillary number), and aspect ratio. First, we focus on the coupling between the shape deformation and orientation dynamics of capsules, and show how this coupling influences the transition from the tank-treading to tumbling motion. At low capillary numbers, three distinct modes of motion are identified: a swinging or oscillatory (OS) mode at a low viscosity contrast in which the inclination angle θ(t) oscillates but always remains positive; a vacillating-breathing (VB) mode at a moderate viscosity contrast in which θ(t) periodically becomes positive and negative, but a full tumbling does not occur; and a pure tumbling mode (TU) at a higher viscosity contrast. At higher capillary numbers, three types of transient motions occur, in addition to the OS and TU modes, during which the capsule switches from one mode to the other as (i) VB to OS, (ii) TU to VB to OS, and (iii) TU to VB. It is shown that the coupling between the shape deformation and orientation is the strongest in the VB mode. The numerical results are compared with the theories of Keller and Skalak, and Skotheim and Secomb. Significant departures from the two theories are discussed and related to the strong coupling between the shape deformation, inclination, and transition dynamics. We then address the rheology of a dilute suspension of liquid-filled elastic capsules. We consider capsules of spherical resting shape for which only a steady tank-treading motion is observed. It is shown that the suspension exhibits a shear viscosity minimum at moderate values of the viscosity ratio, and high capillary numbers. The normal stress differences are shown to decrease with increasing capillary number at high viscosity ratios. Such non-trivial results can neither be predicted by the small-deformation theory, nor can be explained by the capsule geometry alone. Physical mechanisms underlying these novel results are studied by decomposing the particle stress tensor into a contribution due to the elastic stresses in the capsule membrane, and a contribution due to the viscosity differences between the internal and suspending fluids. It is shown that the elastic contribution is shear-thinning, but the viscous contribution is shear-thickening. The coupling between the capsule geometry, and the elastic and viscous contributions is analysed to explain the observed trends in the bulk rheology.
NoteIncludes bibliographical references
Noteby Ram Chandra Murthy Kalluri
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.