Turbulence of swarming sperm

Adama Kpatagnon Creppy (1) , Olivier Praud (1) , Xavier Druart (2) , Philippa L. Kohnke (2) , Franck Plouraboué (1)

1 IMFT - Institut de mécanique des fluides de Toulouse
2 PRC - Physiologie de la reproduction et des comportements [Nouzilly]

Collective motion of self-sustained swarming flows has recently provided examples of small-scale turbulence arising where viscous effects are dominant. We report the first observation of universal enstrophy cascade in concentrated swarming sperm consistent with a body of evidence built from various independent measurements. We found a well-defined k−3 power-law decay of a velocity field power spectrum and relative dispersion of small beads consistent with theoretical predictions in 2D turbulence. Concentrated living sperm displays long-range, correlated whirlpool structures of a size that provides an integral scale of turbulence. We propose a consistent explanation for this quasi-2D turbulence based on self-structured laminated flow forced by steric interactions and alignment, a state of active matter that we call “swarming liquid crystal.” We develop scaling arguments consistent with this interpretation.

Mots clés: Collective dynamics; Swarming flows; Active suspensions

Domaines: Mécanique des fluides [physics.class-ph]; Biophysique [physics.bio-ph]; Biologie de la reproduction

Adama Kpatagnon Creppy, Olivier Praud, Xavier Druart, Philippa L. Kohnke, Franck Plouraboué. Turbulence of swarming sperm. Physical Review E : Statistical, Nonlinear, and Soft Matter Physics, 2015, 92 (3), pp.032722. ⟨10.1103/PhysRevE.92.032722⟩. ⟨hal-01308046⟩