Selection mechanism at the onset of active turbulence

• Published in: Nature physics 2019-04, Vol.15 (4), p.362-366
• Main Authors: Martínez-Prat, Berta, Ignés-Mullol, Jordi, Casademunt, Jaume, Sagués, Francesc
• Format: Article
• Language: English
• Subjects: 639/301/923; 639/766/747; Adenosine triphosphate; Atomic; Classical and Continuum Physics; Complex Systems; Computational fluid dynamics; Condensed Matter Physics; Continuum modeling; Cristalls líquids nemàtics; Defects; Dependence; Dinàmica de fluids; Experiments; Fluid dynamics; Fluid flow; Fourier transforms; Letter; Mathematical and Computational Physics; Molecular; Nematic liquid crystals; Optical and Plasma Physics; Physics; Physics and Astronomy; Stability; Theoretical; Turbulence; Turbulent flow; Turbulència; Wavelengths
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/s41567-018-0411-6

Active turbulence describes a flow regime that is erratic, and yet endowed with a characteristic length scale 1 . It arises in animate soft-matter systems as diverse as bacterial baths 2 , cell tissues 3 and reconstituted cytoskeletal preparations 4 . However, the way that these turbulent dynamics emerge in active systems has so far evaded experimental scrutiny. Here, we unveil a direct route to active nematic turbulence by demonstrating that, for radially aligned unconfined textures, the characteristic length scale emerges at the early stages of the instability. We resolve two-dimensional distortions of a microtubule-based extensile system 5 in space and time, and show that they can be characterized in terms of a growth rate that exhibits quadratic dependence on a dominant wavenumber. This wavelength selection mechanism is justified on the basis of a continuum model for an active nematic including viscous coupling to the adjacent fluid phase. Our findings are in line with the classical pattern-formation studies in non-active systems 6 , bettering our understanding of the principles of active self-organization, and providing potential perspectives for the control of biological fluids. Experiments on microtubule-based nematics, together with active gel theory, suggest that the length scale associated with active turbulence is selected at its onset—balancing activity with the stabilizing effects of nematic elasticity and geometry.