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Effect of fluid and particle inertia on the rotation of an oblate spheroidal particle suspended in linear shear flow

Författare:	Rosén, T., Do-Quang, M., Aidun, C. K., Lundell, F.
Dokumenttyp:	Artikel
Tillstånd:	Publicerad
Tidskrift:	Physical Review E
Volym:	91 053017
År:	2015

Abstract

This work describes the inertial effects on the rotational behavior of an oblate spheroidal particle confined between two parallel opposite moving walls, which generate a linear shear flow. Numerical results are obtained using the lattice Boltzmann method with an external boundary force. The rotation of the particle depends on the particle Reynolds number, Re _p=Gd ²ν ^-1 (G is the shear rate, d is the particle diameter, ν is the kinematic viscosity), and the Stokes number, St=αRer _p (α is the solid-to-fluid density ratio), which are dimensionless quantities connected to fluid and particle inertia, respectively. The results show that two inertial effects give rise to different stable rotational states. For a neutrally buoyant particle (St=Re _p) at low Re _p, particle inertia was found to dominate, eventually leading to a rotation about the particle's symmetry axis. The symmetry axis is in this case parallel to the vorticity direction; a rotational state called log-rolling. At high Rep, fluid inertia will dominate and the particle will remain in a steady state, where the particle symmetry axis is perpendicular to the vorticity direction and has a constant angle φ _c to the flow direction. The sequence of transitions between these dynamical states were found to be dependent on density ratio α, particle aspect ratio r _p, and domain size. More specifically, the present study reveals that an inclined rolling state (particle rotates around its symmetry axis, which is not aligned in the vorticity direction) appears through a pitchfork bifurcation due to the influence of periodic boundary conditions when simulated in a small domain. Furthermore, it is also found that a tumbling motion, where the particle symmetry axis rotates in the flow-gradient plane, can be a stable motion for particles with high r _p and low α.