

Article
Effect of fluid and particle inertia on the rotation of an oblate spheroidal particle suspended in linear shear flow
Authors: 
Rosén, T., DoQuang, M., Aidun, C. K., Lundell, F. 
Document Type: 
Article 
Pubstate: 
Published 
Journal: 
Physical Review E 
Volume: 
91
053017 
Year: 
2015 
AbstractThis 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
^{2}ν
^{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 solidtofluid 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 logrolling. 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 flowgradient plane, can be a stable motion for particles with high r
_{p} and low α.

