Stochastic resonance on the transverse displacement of swimmers in an oscillatory shear flow

TL;DR

This paper investigates how small fluctuations in oscillatory shear flow can enhance the transverse displacement of swimming microorganisms through stochastic resonance, affecting their diffusion and suspension rheology.

Contribution

It demonstrates the occurrence of stochastic resonance in swimmer displacement under oscillatory shear flow, a novel insight into microorganism dynamics in fluctuating environments.

Findings

Transverse displacement is maximized at a specific noise level.

Resonant noise intensity scales with oscillation frequency.

Displacement enhancement impacts diffusion and rheology.

Abstract

Self-propelled microorganisms, such as unicellular algae or bacteria, swim along their director relative to the fluid velocity. Under a steady shear flow the director rotates in close orbit, a periodic structure that is preserved under an oscillatory shear flow. If the shear flow is subjected to small fluctuations produced by small irregularities in the microchannel or by other swimmers nearby, the director dynamics becomes stochastic. Numerical integration of the swimmer motion shows that there is stochastic resonance: The displacement in the vorticity direction is maximized for a finite noise intensity. This transverse displacement resonance is observed when the displacement is coarse grained over several periods, although the director is preferentially oriented along the flow. The resonant noise intensity is proportional to the oscillation frequency and independent of the shear rate. The enhanced displacement can have effects on the transverse diffusion of swimmers and the rheology of the suspension.