A model for alignment between microscopic rods and vorticity

Wilkinson, M. and Kennard, H. R. (2012). A model for alignment between microscopic rods and vorticity. Journal of Physics A: Mathematical and Theoretical, 45 p. 455502.

DOI: https://doi.org/10.1088/1751-8113/45/45/455502

URL: http://iopscience.iop.org/1751-8121/45/45/455502

Abstract

Numerical simulations show that microscopic rod-like bodies suspended in a turbulent flow tend to align with the vorticity vector, rather than with the dominant eignevector of the strain-rate tensor. This paper investigates an analytically solvable limit of a model for alignment in a random velocity field with isotropic statistics. The vorticity varies very slowly and the isotropic random flow is equivalent to a pure strain with statistics which are axisymmetric about the direction of the vorticity. We analyse the alignment in a weakly fluctuating uniaxial strain field, as a function of the product of the strain relaxation time Τs and the angular velocity ω about the vorticity axis. We find that when ωΤs ≫ 1, the rods are predominantly either perpendicular or parallel to the vorticity.

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