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During the processing of nematic soft solids through process flow elements (pipe bends, elbows, etc.), the constitutive behaviour makes its presence felt via processing (with rheology driven effects increasing pressure drop) and the final product microstructure. This paper explores the flow and microstructure configurations of nematic liquid crystals in a pressure driven flow through $90^o$ pipe bends with different types of wall anchoring. The governing equations of the Leslie-Ericksen theory are solved numerically in a newly developed OpenFOAM solver. We show that the bend curvature deforms the nematic axis distribution; the distortion can be driven either by elastic or hydrodynamic effects. The interaction between the nematic microstructure and flow field generates non-zero normal stresses (in the radial, azimuthal and streamwise directions), which produce a secondary flow and increase pressure losses. The strength of the secondary flow depends on the type of wall anchoring and Ericksen number; in configurations with homeotropic anchoring, decreasing the Ericksen number increases the relative strength of the secondary flow (with respect to the mean flow velocity). Conversely, homogeneous (planar) anchoring reduces normal stresses, thus weakening the secondary flow strength. We show that as the fluid enters/leaves the bend, there is a perturbation in the transverse velocity caused by streamwise stress gradients. The perturbation magnitude depends on material properties and can be of different values at the bend exit and entrance. Finally, we show that the spatial development of the nematic field downstream of the bend exit is controlled by both material properties and the Ericksen number.

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Thin films consisting of polymer solutions are typically produced through a combination of extrusion and shearing processes, where the anisotropic, non-Newtonian solution is deformed and subjected to thermal treatment. This paper investigates the shearing of polymeric thin films by studying the channel flow rheology of polymer solutions that experience yield stress. The material rheology is described by the transversely isotropic fluid (TIF) model, which contains a yield behavior term related to microstructure distortion. Our results show that this distortional stress is able to resist the pressure gradient, and non-trivial stress distributions can exist in the absence of a flow. This represents a significant improvement over existing viscosity-based yield stress models (e.g., the Heschel–Bulkley model). The unyielded state is achieved as the end result of a transient process, where a pressure gradient produces a short-lived flow that ceases when opposing stresses from microstructure distortion are produced. Predictions of the TIF model are compared with the phenomenological Saramito model. Both models are found to predict yielding when a threshold stress is exceeded. In both cases, the velocity profile is Newtonian near the wall, while plug flows are encountered close to the centerline.