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Taylor dispersion of gyrotactic swimming micro-organisms in a linear flow

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JournalPhysics of fluids
DatePublished - Aug 2002
Issue number8
Volume14
Number of pages8
Pages (from-to)2598-2605
Original languageEnglish

Abstract

The theory of generalized Taylor dispersion for suspensions of Brownian particles is developed to study the dispersion of gyrotactic swimming micro-organisms in a linear shear flow. Such creatures are bottom-heavy and experience a gravitational torque which acts to right them when they are tipped away from the vertical. They also suffer a net viscous torque in the presence of a local vorticity field. The orientation of the cells is intrinsically random but the balance of the two torques results in a bias toward a preferred swimming direction. The micro-organisms are sufficiently large that Brownian motion is negligible but their random swimming across streamlines results in a mean velocity together with diffusion. As an example, we consider the case of vertical shear flow and calculate the diffusion coefficients for a suspension of the alga Chlamydomonas nivalis. This rational derivation is compared with earlier approximations for the diffusivity. (C) 2002 American Institute of Physics.

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