Intricate dynamics of neutrally suspended triaxial ellipsoids in simple shear flow

As a typical example of non-spherical particles, the dynamics of triaxial ellipsoids in fluids have attracted growing interest. By employing a high-fidelity numerical approach based on the lattice Boltzmann method, we conducted a comprehensive investigation into the rotational characteristics of triaxial ellipsoids in simple shear flow. This study spans a broad range of parameters, including particle aspect ratios, fluid inertia as indicated by the Reynolds number, and particle inertia as represented by the Stokes number. Several key phenomena were observed: (1) Even minimal fluid and particle inertia can drive particles from an initial nonequilibrium state to an equilibrium state, where they exhibit periodic rotation around either the shortest or the intermediate-length principal axis. (2) The transition from the initial nonequilibrium state to the equilibrium state, while complex, demonstrates strong regularity within the phase spaces of particle orientation and angular velocities, with angular velocities showing a notable dependence on the orientation angles of the particle's principal axis. (3) When the lengths of two principal axes of the particle are comparable and the orientation is near the equilibrium position associated with the third axis, the angular velocities around these two axes become coupled. This coupling results in cyclic and progressive evolutionary trajectories, characterized by intricate and elaborate structures in both the orientation and angular velocity spaces. This work offers crucial insights into the distinctive properties of faceted particles across various fields.