Effects of the Non-Newtonian Rheology on the Fluid-Structure Interactions in Biological Flows
Fluid-structure interactions (FSIs) in non-Newtonian fluid flows are found in many industrial processes and biological systems, and the non-Newtonian rheology has significant effects on FSIs. However, it is a challenge to model FSIs involving non-Newtonian flows due to their complex characteristics. In this work, FSIs involving non-Newtonian flows are investigated by the immersed boundary-lattice Boltzmann method (IB-LBM). Firstly, an efficient and accurate IB-LBM solver for FSIs involving non-Newtonian fluids is developed. The governing equations for non-Newtonian fluids are solved by the lattice Boltzmann method. Several solid structures including 2D and 3D rigid and deformable particles, filaments and flags are considered, and the interaction between the fluid and solid structures is achieved by the immersed boundary method. Validation cases against previous experimental and numerical results confirm the accuracy of the present solver. Secondly, the dynamics of 2D and 3D capsules in Newtonian and viscoelastic shear flows is studied. The results show that the Reynolds number, the non-dimensional shear rate, the bending stiffness and the internal-to-external viscosity ratio may influence the behaviours of a capsule in a Newtonian shear flow. In addition, the capsules in viscoelastic shear flows are found to experience smaller deformations at lower Weissenberg numbers (Wi) and continuous increasing deformation when Wi is sufficiently high. Thirdly, the behaviours of a flexible filament in Newtonian and viscoelastic (Giesekus and FENE-CR) uniform flows are investigated. It is found that the Reynolds number promotes the flapping motion of the filament. The viscoelasticity of the Giesekus fluid facilitates the flapping motion of the filament. In contrast, the viscoelasticity of the FENE-CR fluid hinders the flapping motion. Finally, the behaviours of a capsule in a contraction-expansion microchannel are studied. The results show that the capsule tends to focus to different equilibrium trajectories in a Newtonian fluid at a lower confinement depending on the initial position. In contrast, the viscoelasticity of the fluid caused the same equilibrium trajectory which is independent of the initial position of the capsule. In addition, at higher confinement, the capsule migrates to a lower equilibrium trajectory with increasing Wi.
non-Newtonian fluid, fluid-structure interaction, lattice Boltzmann method, immersed boundary method, anzsrc-for: 401212 Non-Newtonian fluid flows (incl. rheology)
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