Non-Brownian fibers commonly flocculate in flowing suspensions at relatively low concentrations (<1% by weight) We have developed a particle-level simulation technique modeling fibers as chains of rods connected by hinges to probe fiber flocculation The model incorporates fiber flexibility, irregular fiber equilibrium shapes, and frictional fiber interactions Model fibers reproduce known orbits of isolated rigid and flexible fibers in shear flow Simulation predictions of first normal stress differences in homogeneously dispersed, dilute flexible fiber suspensions agree with experimental data Fiber features such as flexibility and irregular equilibrium shapes strongly impact single fiber and suspension behavior Fibers aggregate in simulations with interfiber friction, in the absence of attractive forces between fibers Strong flocculation is observed in suspensions of stiff fibers with irregular equilibrium shapes Flocs contain many fibers with three or more contact points, and derive cohesiveness f

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Simulations of fiber flocculation: Effects of fiber properties and interfiber friction

We employ a particle-level simulation technique to investigate the rheology of non-Brownian, flexible fiber suspensions in simple shear flow. The model incorporates a variety of realistic features including fiber flexibility, fiber deformation, and frictional contacts. The viscosity of fiber suspensions is strongly influenced by the fiber equilibrium shape, interfiber friction, and fiber stiffness. The viscosity of the suspension increases as the fiber curvature, the coefficient of friction, or the fiber stiffness is increased. The yield stress of fiber suspensions scales with the volume fraction in a manner similar to that observed experimentally. Fiber suspensions that flocculate exhibit a shear thinning regime that extends to shear rates lower than those observed for homogeneous suspensions.

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Rheology of sheared flexible fiber suspensions via fiber-level simulations

The dynamics and deformations of immersed flexible fibers are at the heart of important industrial and biological processes, induce peculiar mechanical and transport properties in the fluids that c...

https://hal.archives-ouvertes.fr/hal-02167899/document

Dynamics of Flexible Fibers in Viscous Flows and Fluids

A numerical simulation of multiple flexible fibers in suspension in Newtonian simple shear flow is presented. The method used is similar to those of previous recent simulation works by Fan et al. [J. Non-Newtonian Fluid Mech. 74 (1998) 113] and Yamane et al. [J. Non-Newtonian Fluid Mech. 54 (1994) 405], however, the method has been modified to allow a small amount of bending and torsion in the fibers. A restoring moment acts to straighten the fibers as they interact in the flow. It is demonstrated that this simulation can be used to extract basic rheological information about the suspension including fiber orientations and suspension viscosity. The viscosity of semi-concentrated to concentrated flexible fiber suspensions are shown to increase by a magnitude of the order 7–10% greater than the equivalent rigid fiber suspension tested. This is in qualitative agreement with previous experimental work by Goto et al. [Rheologica Acta 25 (1986) 119] and Blakeney [J. Colloid Interface Sci. 22 (1966) 324]. The implication is that any constitutive relation involving particulate suspensions described by orientation vectors may quantitatively underestimate suspension viscosity, particularly for fibers of large aspect ratio, or low Young’s modulus, whereby the tendency to flex is greater [Rheologica Acta 25 (1986) 119]. If particulate deformation were accounted for (by whatever means) in the existing constitutive relationship, predictions of bulk suspension parameters such as viscosity should be noticeably improved. A method is developed to modify an existing rigid-fiber viscosity to an equivalent flexible fiber viscosity, hence improving viscosity prediction ability.

Direct simulation of flexible fibers

Measurement of rheological properties of filamentous fermentation broths

This is the second part of a study examining the mechanical properties and capillary flow of fiber suspensions in Newtonian fluids and in polymer solutions. In part I results for the viscous and elastic properties of the fiber suspensions were presented and it was shown that the fiber suspensions exhibited normal stresses in Newtonian as well as in viscoelastic suspending media. It was thus expected that circulating secondary flows would occur near the entrance to a capillary. Four types of fillers (glass, carbon, nylon and vinylon fibers) suspended in glycerin, HEC solutions and Separan solutions were investigated. The entrance flow patterns were visualized and the pressure fluctuations measured. The visualization enabled the eddies occurring in the fiber suspensions in Newtonian fluids to be analysed and classified into two tpyes. The results from the flow visualization were correlated with the pressure fluctuations. Empirical equations for the tube length correction factor due to the elasticity were obtained.

S. Goto

Papers

The flow behavior of fiber suspensions in Newtonian fluids and polymer solutions. II: Capillary flow