Transport and aggregation of self-propelled particles in fluid flows.

An analysis of the dynamics of prolate swimming particles in laminar flow is presented. It is shown that the particles concentrate around flow regions with chaotic trajectories. When the swimming velocity is larger than a threshold, dependent on the aspect ratio of the particles, all particles escape from regular elliptic regions. For thin rodlike particles the threshold velocity vanishes; thus, the arbitrarily small swimming velocity destroys all transport boundaries. We derive an expression for the minimum swimming velocity required for escape based on a circularly symmetric flow approximation of the regular elliptic regions.