Wall slip effects on the fiber orientation of a short-fiber suspension in hyperbolic channel flow

We investigate the effect of wall fluid slip on the orientation of non-Brownian, short, rigid, and high aspect ratio cylindrical fibers suspended in a Newtonian fluid in flow through a symmetric hyperbolic planar channel. The fiber orientation is described using a second-order tensor formulation that accounts for fiber–fiber interactions and employs a hybrid closure to approximate the fourth-order orientation tensor, while neglecting the extra-stress contribution of the fibers to the total stress tensor. Building on our previous work on the no-slip case (Housiadas, Beris & Advani, J. Rheol. , 2025), the analytical Newtonian velocity field that has been obtained via the extended lubrication theory is utilized (Sialmas & Housiadas, Eur. J. Mech/B Fluids, 2024). Corresponding to this velocity field, the magnitude of the rate-of-deformation decreases as the slip coefficient increases. The resulting equations for the orientation tensor are solved numerically using a fully implicit finite difference method. The results show that the fiber orientation gradually evolves from its initial pure-shear state at the inlet toward a more aligned configuration as the channel exit is approached. The region of higher fiber alignment, that is most pronounced at the midplane where the flow is purely extensional, extends further toward the walls as the slip increases.