Chaos and mixing in micro-biological fluid dynamics: blinking stokeslets

The motion of particles and feeding currents around micro-organisms due to a flagellum are considered. The calculations are pertinent to a range of sessile organisms but we concentrate on fluid motion around Salpingoeca Amphoridium - a choanoflagllate; these are a class of organism in the phylum Protozoa. The flow field is characterized by a very small Reynolds number indicating that viscous forces dominate over inertia. The flow caused by the motion of the flagellum is modelled via a point force. The point of application is not stationary, and this movement is modelled using two stokeslets (appropriate to Stokes' flow) whose orientation and position is varied with time. These sessile micro-organisms reside above a surface, which is modelled as an interface between two fluids having different properties. Efficiency of feeding currents generated by the flagellar motion is studied. The resulting dynamics is investigated using chaotic measures, which examine the stretching and consequent mixing of elements within the fluid. Different point force locations lead to a range of eddy structures such that their superposition results in chaotic advection. Copyright (C) 2001 John Wiley Sons, Ltd.