Shape effects on dynamics of inertia-free spheroids in wall turbulence

Abstract

The rotational motion of inertia-free spheroids has been studied in a numerically simulated turbulent channel flow. Although inertia-free spheroids were translated as tracers with the flow, neither the disk-like nor the rod-like particles adapted to the fluid rotation. The flattest disks preferentially aligned their symmetry axes normal to the wall, whereas the longest rods were parallel with the wall. The shape-dependence of the particle orientations carried over to the particle rotation such that the mean spin was reduced with increasing departure from sphericity. The streamwise spin fluctuations were enhanced due to asphericity, but substantially more for prolate than for oblate spheroids.

Rotation of Nonspherical Particles in Turbulent Channel Flow

“…Recently Voth [33] argued that a weakly-inertial oblate spheroid aligned near the wall-normal direction will spend a long time in this orientation before tumbling. Challabotla et al [34] similarly observed that prolate tracers with their symmetry axis almost aligned in the streamwise direction rarely tumble and the observed orientation and rotation of tracer spheroids in the viscous sub-layer was qualitatively consistent with spheroids in Jeffery orbits in linear shear flow. Thus we conclude that the weak tumbling and spinning for inertia-free spheroids with high aspect ratio can be attributed to Jeffery-like orbiting.…”

Drag reduction in turbulent channel flow laden with finite-size oblate spheroids

“…Turbulent channel flow of non-spherical particles has been investigated by several authors (Zhang et al 2001;Mortensen et al 2008;Marchioli et al 2010;Challabotla et al 2015a), with focus on the particle dynamics. Challabotla et al (2015b) investigated the rotational motion of inertia-free spheroids in turbulent channel flow using the equations by Jeffery (1922) for the particle rotation. These authors showed that oblate spheroids preferentially align their symmetry axes normal to the wall, whereas prolates are preferentially parallel to the wall.…”

Alignment statistics of rods with the Lagrangian stretching direction in a channel flow

“…A natural question to ask is how the presence of walls affects the alignment behaviour of slender rods? Zhao & Andersson (2016) found that elongated rods in a turbulent channel flow align preferentially with the Lagrangian stretching direction, but that the orientation and rotation behaviours appear to depend quite sensitively upon the aspect ratio near the wall (Challabotla, Zhao & Andersson 2015; Zhao et al 2015). Several authors have analysed how the orientation of slender rods aligns with the laboratory-fixed basis of a turbulent channel flow.…”

“…We study how the distribution of relative angles depends on the particle aspect ratio and on the distance of the particle from the channel wall. Our numerical studies employ DNS of a turbulent channel flow with a friction Reynolds number (Challabotla et al 2015).…”