Bioconvection, flowfields and the dispersion of biased swimming micro-organisms in a flow in a tube

Orateur : Martin A. BEES (Department of mathematics)

Accumulations of biased swimming micro-organisms can induce large-scale hydrodynamic instabilities, driving ’bioconvection patterns’ within tens of seconds over length scales of centimetres. For instance, phototactic swimming algae typically swim towards weak light and away from bright light. Many cells are bottom heavy and so, in the absence of shear, swim upwards on average, termed gravitaxis. Also, torques due to bottom-heaviness act in concert with viscous torques and give rise to gyrotactic behaviour : in suspensions of gyrotactic swimming green algae, cells swim towards down-welling regions. In this talk, I shall describe measurements and theory for individuals and how one can scale-up to model a suspension of cells. I shall also discuss the use of differential dynamic microscopy as a high-throughput method to measure attributes of the cells’ swimming motion. And finally, a continuum description will be employed to extend classical Taylor-Aris theory to describe the axial transport of biased swimming cells in a flow in a tube, of potential relevance to the algal biofuels industry.

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