Abstract

Recent experiments have revealed that puller-type Janus microswimmers exhibit upstream swimming in the presence of an externally applied flow [Sharan et al., “Upstream rheotaxis of catalytic Janus spheres,” ACS Nano 16, 4599-4608 (2022)]. Previous theoretical studies had shown that hydrodynamic interactions with adjacent walls can stabilize the upstream motion of puller-type microswimmers. A thermodynamically admissible model that allows coupling fuel consumption with the swimmer's motion is used here to study a swarm. We show that hydrodynamic interactions between the swimmers in the swarm can also stabilize the upstream swimming of puller-type microswimmers. Moreover, stability is maintained for a longer time when the volume fraction of microswimmers is larger. © 2025 Author(s).