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Biological Fluid Dynamics

Bio-convection

 Algae convecting

Credit: Otti Croze

Bioconvection pattern formed by the swimming alga Dunaliella salina, a commercial beta-carotene producer. This species, like many others, is biased by a gravitational torque to swim up. In a flow, an additional viscous toque causes swimming to downwelling fluid (gyrotaxis).

The pattern is the result of overturning (similar to Rayleigh-Bernard convection, but without external energy input!) and gyrotactic instabilities. Similar physics needs to be considered in photobioreactors to grow algae.


Flow field of swimming nematode

C. elegans swimming flow field

Credit: Tom Montenegro-Johnson and Eric Lauga

The nematode worm C. elegans swims by generating travelling undulations along its body, driving a complex, three-dimensional flow that is revealed by our boundary element simulations, based on experimentally-extracted kinematics. Here, we see flow streamlines captured at an instant where the swimmer's body forms an 'S'-shape, where the colour bar gives the flow speed in millimetres per second. Using theoretical fluid dynamics, experimental planar flow fields extracted from particle tracks can be corrected for this three-dimensional motion [preprint].