Direct simulation of flexible fibers

A numerical simulation of multiple flexible fibers in suspension in Newtoni an simple shear flow is presented. The method used is similar to those of p revious 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) 4 05], however, the method has been modified to allow a small amount of bendi ng and torsion in the fibers. A restoring moment acts to straighten the fib ers as they interact in the flow. It is demonstrated that this simulation can be used to extract basic theolo gical information about the suspension including fiber orientations and sus pension viscosity. The viscosity of semi-concentrated to concentrated flexi ble fiber suspensions are shown to increase by a magnitude of the order 7-1 0% greater than the equivalent rigid fiber suspension tested. This is in qu alitative agreement with previous experimental work by Goto et al. [Rheolog ica Acta 25 (1986) 119] and Blakeney [J. Colloid Interface Sci. 22 (1966) 3 24]. The implication is that any constitutive relation involving particulat e suspensions described by orientation vectors may quantitatively underesti mate suspension viscosity, particularly for fibers of large aspect ratio, o r low Young's modulus, whereby the tendency to flex is greater [Rheologica Acta 25 (1986) 1 19]. If particulate deformation were accounted for (by wha tever means) in the existing constitutive relationship, predictions of bulk suspension parameters such as viscosity should be noticeably improved. A m ethod is developed to modify an existing rigid-fiber viscosity to an equiva lent flexible fiber viscosity, hence improving viscosity prediction ability . (C) 2001 Elsevier Science B.V. All rights reserved.