Grégoire Lemoult, Liang Shi, Kerstin Avila, Shreyas V. Jalikop, Marc Avila and Björn Hof.

Nature Physics (2016) 12, 254-258

http://dx.doi.org/10.1038/NPHYS3675

Turbulence is one of the most frequently encountered nonequilibriumphenomena in nature, yet characterizing thetransition that gives rise to turbulence in basic shear flowshas remained an elusive task. Although, in recent studies,critical points marking the onset of sustained turbulence1–3have been determined for several such flows, the physicalnature of the transition could not be fully explained. Inextensive experimental and computational studies we showfor the example of Couette flow that the onset of turbulenceis a second-order phase transition and falls into the directedpercolation universality class. Consequently, the complexlaminar–turbulent patterns distinctive for the onset of turbulencein shear flows4,5 result from short-range interactionsof turbulent domains and are characterized by universalcritical exponents. More generally, our study demonstratesthat even high-dimensional systems far from equilibrium suchas turbulence exhibit universality at onset and that here thecollective dynamics obeys simple rules.