261362 A Micro-Swimmer Model with Dipolar, Quadrupolar and Rotlet Dipolar Flows

Wednesday, October 31, 2012: 2:00 PM
409 (Convention Center )
Ronald G. Larson, University of Michigan, Ann Arbor, MI and Nobuhiko Watari, Macromolecular Science and Engineering, University of Michigan, Ann Arbor, MI

To study the collective swimming of a peritrichous bacterium such as Escherichia coli, we model a micro-swimmer using a Low-Order Multipole Swimming (LOMS) model.  This model consists of an ellipsoidal particle that migrates at a constant velocity along its long axis and generates a flow of a superposition of a Stokeslet dipole, a Stokeslet quadrupole and a Rotlet dipole. The magnitude of these three flow components are found by modeling a single E.coli cell using a bead-spring model containing 120 beads. The bead-spring model accounts for: 1), the hydrodynamic and the mechanical interactions among the cell body and multiple flagella; 2), the reversal of the rotation of a flagellum in a tumble; and 3), the associated polymorphic transformations of the flagellum. Because a flexible hook connects the cell body and each flagellum, the flagella can take independent orientations with respect to the cell body. This simulation reproduces the experimentally observed behaviors of E. coli, including the steady clockwise swimming near a wall. The reduction of this 120-bead model to a simple LOMS is therefore the first multi-scale simulation study on micro- swimmers. On the contrary to the previous study using dipolar flow swimmer, it is found that the hydrodynamic interaction between micro-swimmers gives a significant contribution to the cell-cell scattering, or rotational diffusion of swimmers, mainly because of the higher-order flows, i.e. the Stokeslet quadrupole and Rotlet dipole.

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See more of this Session: Bio-Fluid Dynamics
See more of this Group/Topical: Engineering Sciences and Fundamentals