How inertial lift affects the dynamics of a microswimmer in Poiseuille flow

TL;DR

This paper investigates how small but non-negligible fluid inertia influences the movement of microswimmers in Poiseuille flow, revealing complex behaviors like bistability and a new 'swimming lift' effect.

Contribution

It introduces the concept of a 'swimming lift' caused by active swimming and fluid inertia, expanding understanding beyond passive particle dynamics.

Findings

Identification of a 'swimming lift' effect due to active motion and inertia.

Discovery of bistable states including tumbling and stable centerline swimming.

Sensitivity of dynamics to swimmer type and hydrodynamic signature.

Abstract

We analyze the dynamics of a microswimmer in pressure-driven Poiseuille flow, where fluid inertia is small but non-negligible. Using perturbation theory and the reciprocal theorem, we show that in addition to the classical inertial lift of passive particles, the active nature generates a `swimming lift', which we evaluate for neutral and pusher/puller-type swimmers. Accounting for fluid inertia engenders a rich spectrum of novel complex dynamics including bistable states, where tumbling coexists with stable centerline swimming or swinging. The dynamics is sensitive to the swimmer's hydrodynamic signature and goes well beyond the findings at vanishing fluid inertia. Our work will have non-trivial implications on the transport and dispersion of active suspensions in microchannels.