Meso-scale turbulence in living fluids

By H. H. Wensink, Jörn Dunkel, Sebastian Heidenreich, K. Drescher, Raymond E. Goldstein, Hartmut Löwen, Julia M. Yeomans. Proceedings of the National Academy of Sciences of the United States of America, 2012

893 citations recorded by the source corpus.

Turbulence is ubiquitous, from oceanic currents to small-scale biological and quantum systems. Self-sustained turbulent motion in microbial suspensions presents an intriguing example of collective dynamical behavior among the simplest forms of life and is important for fluid mixing and molecular transport on the microscale. The mathematical characterization of turbulence phenomena in active nonequilibrium fluids proves even more difficult than for conventional liquids or gases. It is not known which features of turbulent phases in living matter are universal or system-specific or which generalizations of the Navier–Stokes equations are able to describe them adequately. Here, we combine experiments, particle simulations, and continuum theory to identify the statistical properties of self-sustained meso-scale turbulence in active systems. To study how dimensionality and boundary conditions affect collective bacterial dynamics, we measured energy spectra and structure functions in dense Bacillus subtilis suspensions in quasi-2D and 3D geometries. Our experimental results for the bacterial flow statistics agree well with predictions from a minimal model for self-propelled rods, suggesting that at high concentrations the collective motion of the bacteria is dominated by short-range interactions. To provide a basis for future theoretical studies, we propose a minimal continuum model for incompressible bacterial flow. A detailed numerical analysis of the 2D case shows that this theory can reproduce many of the experimentally observed features of self-sustained active turbulence.

Subfields: Computer Networks and Communications, Condensed Matter Physics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/f8433b23b8b16a186029ae6f241d166e2e63a8ab

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Citations in the corpus

Physics of microswimmers—single particle motion and collective behavior: a review (2014, methodology): “In assemblies of motile microorganisms, cooperativity reaches a new level as they exhibit highly organized movements with remarkable large-scale patterns such as 33 networks, complex vortices, or swarms (Gachelin et al., 2014; Heinrichsen, 1978; Kearns, 2010; Wensink et al., 2012).”
Topological active matter (2020, background): “The defect-driven chaotic flows lead to a state dubbed ‘active turbulence’ 74,93 , which is characterized by vorticity and shear flows on a typical length scale that controls the mean defect separation and is set by a balance of active and elastic stresses 68,74,94–96 .”
A phase diagram for bacterial swarming (2019, background): “S8-S9, Ramaswamy 2010] and meso-scale turbulence [Wensink 2012], have been inferred from SPP and continuous models and are found, to some extent, in the present experiments.”
Nonequilibrium physics in biology (2019, background): “For biological fluids, the Reynolds number is often low; however, they can still sometimes exhibit turbulent behavior, e.g., in bacterial suspensions (Dombrowski et al., 2004; Wensink et al., 2012).”
Symmetry, Thermodynamics, and Topology in Active Matter (2021, background): “Active fluids with polar symmetry, such as bacterial suspensions [25], bird flocks [2, 15] and dense collections of Quincke rotors [26], can organize in states with macroscopic mean motion - a flock.”
Hydrodynamics of soft active matter (2013, methodology): “Conversely, it was recently argued that the complex turbulent flows of dense bacterial suspensions are well described by a model of an incompressible fluid with overdamped dynamics, effectively equivalent to what is referred to as a dry model in this review (Wensink et al., 2012).”
Active suspensions and their nonlinear models (2013, methodology): “To address this, we and others have found it very useful to study active suspensions as complex fluids, and to employ the tools of continuum mechanics, statistical physics, and coarse-graining to posit or derive continuum partial-differentialequation models [42] [43] [44] [45] [46] [47] [48].”
Tuned, driven, and active soft matter (2015, background): “Apart from that, various different collective states of migration have been revealed for interacting self-propelled rods [453, 462, 484, 488, 489, 491, 492].”
Fluid flows created by swimming bacteria drive self-organization in confined suspensions (2014, background): “2A and SI Movie 1) or a stable ‘bionematic’ state [5] at higher concentration, as classified by [16] and seen in swarming colonies on surfaces [40].”
Active Particles in Complex and Crowded Environments (2016, background): “…and smaller length scales; hence, the active turbulence seen in the microscopic active systems needs a different explanation, although, to date, a unified description of the formation and structure of these patterns remains lacking (Dunkel et al., 2013; Ishikawa et al., 2011; Wensink et al., 2012).”