Preferential Alignment and Heterogeneous Distribution of Non-spherical
Swimmers Near Lagrangian Coherent Structures
Abstract
We report the interaction between non-spherical swimmers and a
long-standing flow structure, Lagrangian coherent structures (LCSs), in
a weakly turbulent two-dimensional flow. Using a hybrid
experimental-numerical model, we show that rod-like swimmers have a much
stronger and more robust preferential alignment with attracting LCSs
than with repelling LCSs. Tracing the swimmers’ Lagrangian trajectories,
we reveal that the preferential alignment is the consequence of the
competition between the intrinsic mobility of the swimmers and the
reorientation ability of the strain rate near the attracting LCSs. The
strong preferential alignment with attracting LCSs further leads to a
strong clustering near the attracting LCSs. Moreover, we show the
self-similarity of this clustering, which reduces the intricate
interaction to only one control parameter. Our results generically
elucidate the interaction between active and non-spherical swimmers with
LCSs and, thus, can be widely applied to many natural and engineered
fluids including ocean flow.