Speaker
Description
Due to their nonequilibrium character, the collective dynamics of swimming microorganisms systems is often dictated by long-ranged hydrodynamic interactions. One example is the collective motion of swimming, rear-actuated (“pusher”) bacteria that interact through their long-ranged dipolar flow fields to create a state of so-called “active turbulence” with chaotic, collective swimming with long-ranged correlations. This behaviour is in contrast to the behaviour of front-actuated (“puller”) organisms such as certain algae, that do not exhibit any collective motion in 3 dimensions. In this talk, I will summarize theoretical and computational results that provide new information about the transition to active turbulence in both unbounded and confined systems. Our results reveal a qualitatively different behaviour of microswimmers in quasi-2D confinement compared to the unbounded case, where the long-ranged instability leading to active turbulence in 3D is instead rendered short-ranged. Additionally, we find a previously uncharted density instability of confined puller microswimmers, which has no counterpart in unbounded systems. Our results thus highlight that the details of the experimental geometry is crucial for collective phenomena in active matter dominated by hydrodynamic interactions.
