Influence of the quiescent core on tracer spheroidal particle dynamics in turbulent channel flow

Numerical studies into the dynamics of non-spherical particles in turbulent channel flow have, until now, been mostly confined to low Reynolds numbers. In this paper, we investigate the dynamics of tracer non-spherical particles in a channel flow at for the first time. Tracer spheroidal particles suspended in a turbulent channel flow are computed by means of direct numerical simulation coupled with a Lagrangian point-particle approach. We examine the rotational dynamics and alignment of tracer spheroids of different aspect ratio in both the near-wall region and, in particular, the quiescent core which is not observed at lower Reynolds numbers. In the near-wall region, the effect of Reynolds number on preferential alignment is negligible with particle rotation exhibiting a weak dependence for all aspect ratios investigated. However, the particle rotation is strongly damped in the quiescent core demonstrating that the motion of tracer spheroids becomes quiescent. The striking difference in spheroids' rotational dynamics observed inside and outside of the quiescent core is correlated with the local Kolmogorov time scale in the core and outside of it.