Chiral Particles in Taylor-Couette Turbulence

TL;DR

This study examines large chiral particles in turbulent Taylor–Couette flow over $9.5 \times 10^{3} \le \mathrm{Re} \le 1.5 \times 10^{5}$. Using density-matched, dilute suspensions and 3D tracking of position and orientation, it finds that particles closely follow Taylor vortices and that their orientation and rotation are governed by the flow rather than chirality, with no translation–rotation coupling discernible between left- and right-handed particles. The angular velocity magnitude increases with Reynolds number, and orientation densities remain uniform, indicating flow-dominated dynamics. A particle timescale analysis shows $\tau_d/\tau_\eta \propto \mathrm{Re}^{0.47}$, aligning with turbulence-driven scaling and supporting the conclusion that chirality effects are washed out at high Re. These results illuminate the regime where chiral particle dynamics give way to flow-dominated behavior in anisotropic turbulence, and they motivate exploration of intermediate Re regimes to map the onset of chirality-driven effects.

Abstract

This work investigates chiral particles, which break mirror symmetry, in turbulent Taylor--Couette flow. These particles generally display a translation-rotation coupling moving through a quiescent fluid. Here we performed experiments using large chiral particles (typical size \unit{5}{mm}) in turbulent Taylor--Couette flow, for Reynolds numbers $9\cdot10^3 \leq \text{Re} \leq 1.5 \cdot 10^5$. The density-matched chiral particles are studied in a dilute regime $(φ= 1.7 \cdot 10^{-4})$, where their location and orientation are tracked over time to investigate the particle-fluid coupling. We investigate whether the translation-rotation coupling observed at low Reynolds numbers is still observable over the measured high Reynolds numbers, using the tracked location and orientation. Similarly, we verify whether the chiral particles display a preferred location or orientation, and whether the left-handed and right-handed particles show different rotation statistics. The location data show that the chiral particles closely follow the structure of Taylor vortices. Hence, the orientation data and rotation data of the chiral particles are split between the Taylor vortices and particle chiralities. The results show no difference in rotation and orientation dynamics between chiralities. Rather, the particle dynamics are flow-dominated, where the flow vorticity determines the specific particle dynamics.

Figures (14)

• Figure 1: (a) Synthetic 3D representation of the chiral particles used in this research. (b) Photograph of the chiral particles used in the Taylor--Couette facility. Both left-handed and right-handed particles are shown in the image.
• Figure 2: Trajectories of heavy settling chiral particles in quiescent flow for both particle chiralities. The difference in rotation direction is highlighted by the trajectories of the endpoints of the particle. These trajectories are obtained from experimental measurements, performed similarly to the measurements as described in Section \ref{['sec:Method and setup']}.
• Figure 3: (a) Image of the used Taylor--Couette setup with 4 high-speed cameras used to image particles at (approximately) mid-height of the setup. (b) Schematic of the Taylor--Couette setup and the coordinate system in the lab frame. The measurement volume is shown in red, the blue arrow shows the direction of the dominant flow.
• Figure 4: (a) A typical image captured by a high-speed camera during a measurement. Chiral particles are visible as grey shapes. Image was taken for a measurement with both particle chiralities at $\text{Re} = 3.8 \cdot 10^4$. (b) Reconstructed 3D chiral particles, constructed using tracking methods described in previous work Flapper2024. An animation of a raw recording alongside the particle reconstruction is included in the supplementary material.
• Figure 5: a) All particle location tracks for $\text{Re} = 1.5 \cdot 10^5$. The dominant azimuthal velocity is from left to right in this visualisation. Black lines are added for illustrating the boundaries of the vortices. The vertical dimension has its origin at the mid-height of the cylinder. The horizontal dimension is centred around the middle of the inner cylinder. b) A vector plot of the radial and axial velocity components of the particles, taken in a radial slice of the measurement volume, also for $\text{Re} = 1.5 \cdot 10^5$.