Shape-dependence of particle rotation in isotropic turbulence

TL;DR

This study investigates how particle shape influences rotation in isotropic turbulence, revealing shape affects orientation and tumbling but not angular velocity variance, with complementary effects on spinning rate.

Contribution

It provides a comprehensive analysis combining experiments, simulations, and theory to show shape-dependent effects on particle rotation and orientation in turbulence.

Findings

Shape strongly influences orientational trajectories.

Shape has negligible effect on angular velocity variance.

Tumbling and spinning rates show complementary shape-dependent trends.

Abstract

We consider the rotation of neutrally buoyant axisymmetric particles suspended in isotropic turbulence. Using laboratory experiments as well as numerical and analytical calculations, we explore how particle rotation depends upon particle shape. We find that shape strongly affects orientational trajectories, but that it has negligible effect on the variance of the particle angular velocity. Previous work has shown that shape significantly affects the variance of the tumbling rate of axisymmetric particles. It follows that shape affects the spinning rate in a way that is, on average, complementary to the shape-dependence of the tumbling rate. We confirm this relationship using direct numerical simulations, showing how tumbling rate and spinning rate variances show complementary trends for rod-shaped and disk-shaped particles. We also consider a random but non-turbulent flow. This allows us to explore which of the features observed for rotation in turbulent flow are due to the effects of particle alignment in vortex tubes.