Elliptical Tracers in Two-dimensional, Homogeneous, Isotropic Fluid Turbulence: the Statistics of Alignment, Rotation, and Nematic Order

TL;DR

This study investigates how elliptical tracer particles orient and rotate in two-dimensional turbulence, revealing differences based on forcing scales and particle aspect ratios, with implications for understanding fluid-particle interactions.

Contribution

It provides a comparative analysis of particle orientation and rotation statistics in 2D turbulence under different forcing scales, highlighting the effects of aspect ratio and flow conditions.

Findings

Large-scale forcing creates large-scale orientation structures.

Rotation rate statistics are weakly dependent on Reynolds number.

Mean-square rotation rate decreases with increasing aspect ratio in 2D.

Abstract

We study the statistical properties of orientation and rotation dynamics of elliptical tracer particles in two-dimensional, homogeneous and isotropic turbulence by direct numerical simulations. We consider both the cases in which the turbulent flow is generated by forcing at large and intermediate length scales. We show that the two cases are qualitatively different. For large-scale forcing, the spatial distribution of particle orientations forms large-scale structures, which are absent for intermediate-scale forcing. The alignment with the local directions of the flow is much weaker in the latter case than in the former. For intermediate-scale forcing, the statistics of rotation rates depends weakly on the Reynolds number and on the aspect ratio of particles. In contrast with what is observed in three-dimensional turbulence, in two dimensions the mean-square rotation rate decreases as the aspect ratio increases.