Role of Correlations in the Collective Behavior of Microswimmer Suspensions

Joakim Stenhammar (1) , Cesare Nardini (2, 3, 4) , Rupert W Nash (5) , Davide Marenduzzo (3) , Alexander A Morozov (3)

1 Lund University [Lund]
2 SPHYNX - Systèmes Physiques Hors-équilibre, hYdrodynamique, éNergie et compleXes
3 University of Edinburgh
4 DAMTP - Department of Applied Mathematics and Theoretical Physics
5 EPCC [Edinburgh]

In this Letter, we study the collective behavior of a large number of self-propelled microswimmers immersed in a fluid. Using unprecedentedly large-scale lattice Boltzmann simulations, we reproduce the transition to bacterial turbulence. We show that, even well below the transition, swimmers move in a correlated fashion that cannot be described by a mean-field approach. We develop a novel kinetic theory that captures these correlations and is nonperturbative in the swimmer density. To provide an experimentally accessible measure of correlations, we calculate the diffusivity of passive tracers and reveal its nontrivial density dependence. The theory is in quantitative agreement with the lattice Boltzmann simulations and captures the asymmetry between pusher and puller swimmers below the transition to turbulence.

Domains: Physics [physics]

Joakim Stenhammar, Cesare Nardini, Rupert W Nash, Davide Marenduzzo, Alexander A Morozov. Role of Correlations in the Collective Behavior of Microswimmer Suspensions. Physical Review Letters, 2017, 119, pp.028005. ⟨10.1103/PhysRevLett.119.028005⟩. ⟨cea-01687396⟩