Fluid-inertia torque on spheroids in pseudo-plastic fluid flows: effect of shear-thinning rheology

Abstract

Fluid-inertia torque remarkably affects the orientation of non-spherical particles in Newtonian flows whereas this torque induced by convective fluid inertia in particle-laden pseudo-plastic flows is still unknown. In the present study we numerically investigate the fluid-inertia torque on a neutrally buoyant spheroid in the Carreau-type pseudo-plastic fluid flows at finite Reynolds numbers with the immersed boundary method. The results show that compared with the fluid-inertia torque in Newtonian flows, the magnitude of the fluid-inertia torque on spheroids is remarkably attenuated by the shear-thinning rheology in pseudo-plastic fluid flows. The deviation of fluid-inertia torque between pseudo-plastic and Newtonian flows is more significant with decreasing Reynolds numbers, indicating the importance of the effect of shear-thinning rheology at small Reynolds numbers. Moreover, the spheroid rotation rate is reduced in pseudo-plastic fluids, and the equilibrium orientation of oblate spheroids changes non-monotonically with the shear-thinning effect in the linear shear flow of pseudo-plastic fluids. The present findings imply the importance of the effect of shear-thinning rheology on the torques of spheroids, which could be potentially applied for the control of particle orientations in pseudo-plastic fluids in the future.