Oscillation migration of a neutrally buoyant oblate spheroid in the elasto-inertial duct flow

The peculiar migration and rotational dynamics of non-spherical particles in non-Newtonian flows stem from the interplay between fluid rheology and fluid inertial effects. In this paper, the cross-flow migration of a neutrally buoyant oblate spheroid (aspect ratio $AR = 0.5$ ) immersed in the elasto-inertial duct flow is investigated by particle-resolved simulations with the immersed boundary method. Different from spherical particles, due to the orientation-dependent lift force, the oblate spheroid migrates in an oscillating manner in the duct. The travelling period for particles reaching the duct centreline undergoes a non-monotonic change with elastic number, revealing the existence of a critical elastic number governing the migrating efficiency of oblate particles within the present flow system. For the particle rotation and orientation, the present results indicate that the particle rotation rate and orbit drifting rate are both hindered by the fluid elasticity. With increasing the fluid elasticity, three different orientation modes – log-rolling mode, kayaking-like mode and longside-flow alignment mode – are observed successively during the elasto-inertial migration of the oblate spheroid. Potentially, the present results could be used to design the rheology-based controlling strategy for guiding particles to achieve optimal focusing and orientation in microfluidic applications without the need for external forcing fields.