Fiber alignment in oscillating confined shearing flows

Abstract

Fiber orientation in oscillatory shearing flow was studied both experimentally and numerically. Optical measurements were made using a custom flow cell containing rigid, noncolloidal fibers suspended at high concentration in a Newtonian fluid. Simulations that account for hydrodynamic drag and excluded volume predict fiber alignment in the vorticity direction for some conditions, in agreement with the measurements. Vorticity alignment was found to be a complex function of strain amplitude and fiber concentration, confinement, and aspect ratio.

Advances in the Rheological Characterization of Slurries of Elongated Particles

“…10b which compares the initial and final distribution of the fibers predicted by simulations. Note that the simulated values of S θ quantitatively matched the experimental results over a wide range of conditions (Strednak et al, 2021). Franceschini et al (2014) suggested that the transition in S θ and η'' is controlled by a critical effective volume fraction (Φ c ) of the suspension.…”

“…Measurements (Franceschini et al, 2011;Strednak et al, 2021) and simulations (Snook et al, 2012;Strednak et al, 2021) of the orientation distribution under oscillatory flows also demonstrate a remarkable transition in the alignment as a function of strain amplitude. As shown in Fig.…”

“…9b). Strednak et al (2021) found that the maximum value of S θ declined when the gap spacing H was increased while holding the fiber length L constant, both in experiments and simulations. This indicates that the vorticity alignment of the fibers is promoted by the bounding walls, as was speculated by Snook et al (2012).…”

“…The result for γ 0 < 2.60 marks a transition between vanishing and persistent values for η''. b) Simulated predictions (Strednak et al, 2021) and an experimental measurement (Franceschini et al, 2014) of the microstructure S θ at steady state as a function of the rescaled strain amplitude, γ 0 ϕ/Φ c . A value of 0.4 was used for Φ c .…”

“…The critical effective volume fraction, Φ c defines the combination of volume fraction ϕ and strain displacement γ 0 at which the particles are forced to contact. For oscillatory shear below Φ c , Franceschini et al (2014) speculated that η'' disappears as the suspension rearranges to avoid contact, though simulations indicate that at least some contacts persist (Snook et al, 2012;Strednak et al, 2021). Above Φ c , contacts between particles must occur during the course of every oscillation and η'' remains finite.…”