Turbulent Fluid Acceleration Generates Clusters of Gyrotactic Microorganisms

Filippo de Lillo (1) , Massimo Cencini (2) , William M. Durham (3) , Michael Barry (4) , Roman Stocker (4) , Eric Climent (5) , Guido Boffetta (1)

1 UNITO - Università degli studi di Torino = University of Turin
2 CNR - National Research Council of Italy | Consiglio Nazionale delle Ricerche
3 University of Oxford
4 MIT - Massachusetts Institute of Technology
5 IMFT - Institut de mécanique des fluides de Toulouse

The motility of microorganisms is often biased by gradients in physical and chemical properties of their environment, with myriad implications on their ecology. Here we show that fluid acceleration reorients gyrotactic plankton, triggering small-scale clustering.We experimentally demonstrate this phenomenon by studying the distribution of the phytoplankton Chlamydomonas augustae within a rotating tank and find it to be in good agreement with a new, generalized model of gyrotaxis. When this model is implemented in a direct numerical simulation of turbulent flow, we find that fluid acceleration generates multifractal plankton clustering, with faster and more stable cells producing stronger clustering. By producing accumulations in high-vorticity regions, this process is fundamentally different from clustering by gravitational acceleration, expanding the range of mechanisms by which turbulent flows can impact the spatial distribution of active suspensions.

Mots clés: Micro-organisms; Turbulence

Domaines: Mécanique des fluides [physics.class-ph]

Filippo de Lillo, Massimo Cencini, William M. Durham, Michael Barry, Roman Stocker, et al.. Turbulent Fluid Acceleration Generates Clusters of Gyrotactic Microorganisms. Physical Review Letters, 2014, vol. 112 (n° 4), pp. 044502. ⟨10.1103/PhysRevLett.112.044502⟩. ⟨hal-01303793⟩