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