Richard J.A.M. Stevens

Physics of Fluids

University of Twente

Publication 95 · Wall-shear turbulence

How Taylor vortices trap and align prolate particles

M.P.A. Assen, C.S. Ng, J.B. Will, R.J.A.M. Stevens, D. Lohse, and R. Verzicco, Journal of Fluid Mechanics 935, A7 (2022).

The article and figure are open access under CC BY 4.0.

Main finding

In the tested Taylor-vortex flows, larger prolate ellipsoids clustered near vortex cores and developed a sharp tangential alignment. The strongest alignment coincided with low local axial vorticity and reduced particle rotation, but causality was not independently isolated.

Normalized orientation-width minima versus Taylor number for prolate ellipsoids with major-axis lengths 0.1 and 0.2 gap widths
How to read the figure. The normalized width w/π measures the spread of the particle-orientation distribution; a smaller value means sharper preferred alignment. The solid red curve denotes particles with major-axis length ℓ/d = 0.1 and the dashed blue curve ℓ/d = 0.2. Their minima occur near Ta ≈ 7 × 105 and 4 × 105, respectively. This Figure 7 crop shows only the alignment-width result. Figures 3–4 provide the separate clustering evidence, Figures 5–6 the orientation distributions, and Figures 8–9 the axial-vorticity and reduced-rotation association; none independently isolates causality. Open the full-resolution figure. Figure 7, cropped. M.P.A. Assen et al. (2022), CC BY 4.0.

Why this matters

The study connects finite-size particle position and orientation to the coherent Taylor-vortex structure instead of treating turbulent alignment as spatially uniform. Stable vortex cores preferentially contain the larger particles, while low local axial vorticity coincides with reduced tumbling and sharp alignment with the local cylinder tangent. These observations form a supported association, not an independently controlled causal chain.

Research context

The study uses interface-resolved, two-way-coupled DNS with 16 dilute, neutrally buoyant prolate ellipsoids per run. The ellipsoids have aspect ratio 4 and major-axis lengths ℓ/d = 0.1 or 0.2; the corresponding particle volume fractions are 0.01% and 0.07%. The radius ratio is 5/7, only the inner cylinder rotates, and 3.9 × 104 ≤ Ta ≤ 9.8 × 107, spanning Taylor-vortex, wavy-vortex, and turbulent Taylor-vortex states. Particle size, loading, Stokes response, and flow regime are not independently varied, so their effects cannot be separated. The simulations use one particle shape, density ratio, radius ratio, roll wavelength, and reduced azimuthal domain. With 16 particles and finite averaging, the findings do not establish behavior for oblate, polydisperse, dense, buoyant, or substantially higher-Reynolds-number suspensions.

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