Inertial migration of a neutrally buoyant oblate spheroid in three-dimensional square duct poiseuille flows

Abstract

In this paper, the inertial migration of a single neutrally buoyant oblate spheroid in a square duct is investigated by multiple-relaxation-time lattice Boltzmann method. The spheroid’s aspect ratio AR=a/b=1/2, where a and b are the polar and equatorial radii of the spheroid, respectively, Reynolds number Re=UmH/ν=80 with Um, H and ν being the maximum velocity in the duct without the particle, height of the duct and the kinematic viscosity, respectively, and a blockage ratio 2b/H=0.277 is chosen to study the effects of initial position and initial orientation on the particle’s motion in detail. Our results show that the lateral trajectory and final motion, to some extent, depend on the spheroid’s initial position and orientation. In addition to the general log-rolling (LR) mode, which was previously reported by Lashgari et al. (2017), the spheroid can also exhibit a tumbling (TU) mode, where its polar axis rotates in the central streamwise–wall-normal plane, and an inclined log-rolling (ILR) mode, where it rotates in the diagonal plane with the polar axis being perpendicular to the plane, when its initial position and orientation are well specified. With the Reynolds number increased to 160, the ILR mode disappears while the TU and LR modes persist. If AR decreases to 1/3 while keeping the particle’s volume fixed, all three modes persist at Re=80, and the particle migrates closer to the duct center at the final equilibrium state with decreasing AR for all three different modes.