Analysis of rheological properties of fibre suspensions in a Newtonian fluid by direct fibre simulation. Part 2: Flexible fibre suspensions

Flexible fibre suspensions in a Newtonian fluid experimentally show shear-thinning and normal stress differences in steady state. This paper discusses properties of the shear viscosity, η, and the first and second normal stresses, N1 and N2, using the help of direct fibre simulation based on PSM (particle simulation method), considering near-field hydrodynamic interactions, collision without attractively interacting forces and friction forces between fibres. The software reproduces the tendencies obtained experimentally such as shear-thinning and decreasing N1. In addition to this result, when the aspect ratio is low (<10) and the volume fraction varies between ϕv = 0.05 and 0.1, shear-thickening and increasing N1 are predicted. These tendencies are analyzed using the orientation of the end-to-end vector and the radius of gyration. The prediction of N2 as a function of γ˙ is also shown in the paper.