Paper Number
CR5 

Session
Computational Rheology

Title
Large-amplitude oscillatory shear (LAOS) of a dilute suspension of Brownian spheroids

Presentation Date and Time
October 9, 2017 (Monday) 11:30

Track / Room
Track 6 / Aspen

Authors (Click on name to view author profile)

1. Bechtel, Toni M. (Carnegie Mellon University, Chemical Engineering)
2. Khair, Aditya S. (Carnegie Mellon University, Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Toni M. Bechtel and Aditya S. Khair
Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213

Speaker / Presenter 
Bechtel, Toni M.

Text of Abstract
The stress in a dilute suspension of monodisperse, rigid, Brownian spheroids is calculated under a large-amplitude oscillatory shear (LAOS) deformation. This is achieved by first numerically solving the Fokker-Planck equation for the orientational distribution function over a range of Weissenberg (Wi) and Deborah (De) numbers. Then, the stress tensor is determined from an orientational average of the stresslet exerted by the particles onto the suspending medium. Under a small-amplitude oscillatory shear (SAOS) deformation, where Wi << 1, the stress dynamics are relatively insensitive to the microstructure of the suspension, as parameterized by the aspect ratio (r) of the particles. Specifically, the shear stress can simply be represented by a single Fourier mode (in the flow frequency) for aspect ratios ranging from rods (r >> 1), to near-spheres (r ~ 1), to thin disks (r <<1). However, under LAOS, where Wi >> 1 and Wi/De > 1, the stress dynamics are distinctly dependent upon the microstructure. The shear stress evolution of slender rods will exhibit quasi-steady behavior, which is periodically interrupted by sharp variations when the imposed flow momentarily vanishes. Conversely, the shear stress of a dilute suspension of nearly-spherical particles will mainly undergo rapid oscillations, followed by markedly slower oscillations when the imposed flow momentarily vanishes. Thus, our results indicate that LAOS is a useful tool to probe the dynamics of the microstructure in shear.