Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway

Understanding the dynamics of anisotropic particles in a turbulent carrier fluid over a solid wall is of fundamental interest and a key in making advances in many natural and industrial processes, as well as in bio-fluids applications: the dispersal of plant seeds with irregular shapes, pulp fibres in papermaking, suspensions of bio-mass particles in a burner, and the inhaled non-spherical particles in the human respiratory system. The dynamics of particles with anisotropic shapes are commonly investigated by assuming regular axisymmetric shapes, i.e. either prolate (rod-like) or oblate (disk-like) spheroids. Spheroidal particles interact with wall turbulent flow in complex ways depending on various factors: near-wall shear, turbulence structure, and particle shape and inertia.  The present work is carried out with focus on the inertial effect and wall shear effect on the dynamics of turbulent suspensions of spheroids by means of direct numerical simulations (DNSs) with an Eulerian-Lagrangian formulation. The point-particle approach is adopted and one-way coupling is justified for sufficiently dilute suspensions. Both prolate and oblate spheroids are explored with aspect ratio ranging from 0.01 to 50 and Stokes numbers from 0 (tracers) to 30 (inertial particles). The results for spheroids are compared with the simpler case of spherical particles to highlight the shape effect. The statistical results show that mean particle spin was reduced with increasing departure from sphericity at low particle inertia while this trend was weakened with increasing inertia. Such influences on the spheroids’ rotation are due to the preferential spheroid orientation near the wall which is strongly dependent on particle inertia and shape. We observed that the flattest tracer disks preferentially aligned their symmetry axes normal to the wall whereas the longest tracer rods were parallel with the wall, as shown in Figure 1 (shape effect). With an increase of particle inertia the flat disk-like particle preferentially orients its symmetry axis in the spanwise direction (Challabolta et al. 2015) but the preferential orientation of inertial long rods becomes more isotropic (Zhao et al. 2014).  The different dynamics of the preferential partical orientations will furthermore influence the particle clustering in the near-wall region. Additional results and further discussions will be provided in the presentation.