Preferential alignment and heterogeneous distribution of active non-spherical swimmers near Lagrangian coherent structures

Abstract

We report the interaction between active 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 accumulation near the attracting LCSs. Moreover, we show the self-similarity of this accumulation, 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.

Enhancing transport barriers with swimming micro-organisms in chaotic flows

“…temperature, oxygen and nutrients) in chaotic flows with non-trivial vortex structures. Although there have been previous studies on the interaction between micro-organisms and LCSs (Khurana & Ouellette 2012;Dehkharghani et al 2019;Ran et al 2021;Si & Fang 2021Yoest et al 2022), our work extends the study of micro-organism LCSs interaction to elliptic LCSs (i.e. vortex-like dynamical structures).…”

“…Recently, it has been shown that Lagrangian coherent structure (LCS) can be a useful concept to understand the transport properties of swimming micro-organisms in complex flows in both numerical simulations and experiments (Khurana & Ouellette 2012;Dehkharghani et al 2019;Ran et al 2021;Si & Fang 2021Yoest et al 2022). Simulations in chaotic flows show that elongated swimmers align with repelling LCSs of hyperbolic fixed points (Khurana & Ouellette 2012), while later numerical studies show that elongated active particles have a much stronger alignment with attracting LCSs (Si & Fang 2021, similar to passive elongated particles (Parsa et al 2011). Experimental investigations that examine the interactions of swimming organisms and flow LCSs are few but show some intriguing phenomena.…”

“…2022). Simulations in chaotic flows show that elongated swimmers align with repelling LCSs of hyperbolic fixed points (Khurana & Ouellette 2012), while later numerical studies show that elongated active particles have a much stronger alignment with attracting LCSs (Si & Fang 2021, 2022), similar to passive elongated particles (Parsa et al. 2011).…”

On the Semi-Analytical Solutions in Hydrodynamics of Ideal Fluid Flows Governed by Large-Scale Coherent Structures of Spiral-Type

“…In addition, some remarkable articles should be cited, which concern the problem under consideration [12][13][14][15][16][17][18]. In [12], the formation and shedding of vortices in two vortex-dominated flows around an actuated flat plate are studied to develop a better method of identifying and tracking coherent structures in unsteady flows.…”

“…In [13], authors model the ionospheric-thermospheric flows with the Thermosphere-Ionosphere-Electrodynamics General Circulation Model and identify the Lagrangian coherent structures, which are objective ridges in time-evolving flows that describe the tendency of neighboring fluid elements to separate, providing a unique opportunity to infer the dynamics in the ionospheric-thermospheric system. In [14], it was reported the interaction between active non-spherical swimmers and a long-standing flow structure (Lagrangian coherent structures), in a weakly turbulent two-dimensional flow by using a hybrid experimental-numerical model. In [15], the unsteady phenomena of vertical-axis turbine wake-flow were analyzed in two rotational speed conditions from a Lagrangian perspective.…”