Anisotropic particles in twodimensional convective turbulence
Abstract
The orientational dynamics of inertialess anisotropic particles transported by twodimensional convective turbulent flows display a coexistence of regular and chaotic features. We numerically demonstrate that very elongated particles (rods) align preferentially with the direction of the fluid flow, i.e., horizontally close to the isothermal walls and dominantly vertically in the bulk. This behavior is due to the presence of a persistent large scale circulation flow structure, which induces strong shear at wall boundaries and in up/downwelling regions. The nearwall horizontal alignment of rods persists at increasing the Rayleigh number, while the vertical orientation in the bulk is progressively weakened by the corresponding increase in turbulence intensity. Furthermore, we show that very elongated particles are nearly orthogonal to the orientation of the temperature gradient, an alignment independent of the system dimensionality and which becomes exact only in the limit of infinite Prandtl numbers. Tumbling rates are extremely vigorous adjacent to the walls, where particles roughly perform Jeffery orbits. This implies that the rootmeansquare nearwall tumbling rates for spheres are much stronger than for rods, up to O (10 ) times at Ra ≃ 10^{9}. In the turbulent bulk, the situation reverses and the rods tumble slightly faster than isotropic particles, in agreement with earlier observations in twodimensional turbulence.
 Publication:

Physics of Fluids
 Pub Date:
 February 2020
 DOI:
 10.1063/1.5141798
 arXiv:
 arXiv:1910.02882
 Bibcode:
 2020PhFl...32b3305C
 Keywords:

 Condensed Matter  Soft Condensed Matter;
 Physics  Fluid Dynamics
 EPrint:
 manuscript + additional materials