Blood is a non-homogeneous fluid that flows inside the human artery system and provides the cells with nutrients. In this study the auto rotation effect of blood’s microstructure on its flow inside a human carotid model is studied by using a micropolar fluid model. The study aims to investigate the flow differences that occur due to its microstructure as compared to a Newtonian fluid. We focus on the vortex viscosity effect, i.e., the ratio of microrotation viscosity to the total one, because this is the only parameter that affects directly the fluid flow. Simulations in a range of vortex viscosities, are carried out in a $3D$ human carotid model that is computationally reconstructed. All of the simulations are conducted at the diastolic Reynolds number that occurs in the human carotid. Results indicate that micropolarity affects blood velocity in the range of parameters studied by $4\%$. As micropolarity is increased, higher velocities in the center of vessels and lower near the boundaries are found as compared to a Newtonian fluid consideration. This is an indication that the increase of the fluid’s micropolarity leads to an increase of the boundary layer thickness. More importantly, an increase in vortex viscosity and the resulting increase in microrotation result in decreased shear stress in the carotid’s walls; this finding can be significant in regards to the onset and the development of atherosclerosis. Finally, the flow distribution at the carotid seems to heavily be affected by the geometry and the micropolarity of the fluid.

This direct numerical study investigated the effect of orientational randomness on the barrier properties of flake-filled composites. Over 2500 simulations have been conducted in two-dimensional, doubly periodic unit cells, each containing 500 individual flake cross-sections which, besides being spatially random, assume random orientations within an interval [−ɛ, +ɛ] ([ ]). We consider long flake systems (aspect ratio α = 50, 100, and 1000) from the dilute (αϕ = 0.01) to the concentrated (αϕ = 15) regime, where (ϕ) is the flake volume fraction. At each (ɛ) and (αϕ), several realizations are generated. At each of those, the steady-state diffusion equation is solved, the mass flux across a boundary normal to the diffusion direction is computed and an effective diffusivity D_eff calculated from Fick’s Law. The computational results for D_eff are analyzed and the effects of (ɛ) and (αϕ) are quantified. These differ in the dilute (αϕ < 1) and in the concentrated regimes (1 < αϕ < 15). In the dilute regime, the barrier improvement factor is a linear function of (ɛ) and a power function of (αϕ), with the exponent (∼1.07) independent of orientation. In concentrated systems, we find that for aligned flakes or flakes showing small deviations from perfect alignment, the barrier improvement factor approaches the quadratic dependence on (αϕ) predicted by theory. However, the power exponent is found to decrease as (ɛ) increases, from 1.71 in the aligned system (ɛ = 0) to ∼0.9 in the fully random system (ɛ = π/2). We propose a scaling which incorporates the effects of both (αϕ) and (ɛ) on the barrier improvement factor, resulting in a master curve for all (αϕ) and (ɛ). Our results suggest that the anticipated barrier property improvement may not be realized if the flake orientations exhibit a significant scatter around the desired direction.