The rise of fully turbulent flow

• Published in: Nature (London) Vol. 526; no. 7574; pp. 550 - 553
• Main Authors: Barkley, Dwight, Song, Baofang, Mukund, Vasudevan, Lemoult, Grégoire, Avila, Marc, Hof, Björn
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 22.10.2015; Nature Publishing Group
• Subjects: 639/705/1041; 639/766/189; 639/766/530; Humanities and Social Sciences; letter; multidisciplinary; Observations; Pipe flow; Reynolds number; Science; Shear flow; Turbulence; Turbulent flow; Velocity
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature15701

Experiments, asymptotic theory and computer simulations of wall-bounded shear flow uncover a bifurcation scenario that explains the transition from localized turbulent patches to fully turbulent flow. Turbulent flow diagrams A fluid or gas passing through a pipe will flow smoothly at low speeds but turbulently at high speeds. The transition between these two regimes is complex, with turbulent disturbances first appearing as localized patches that can behave in a variety of different ways depending on the precise flow conditions — decaying, splitting or expanding. Björn Hof and colleagues look at this transition regime in detail, mapping out the behaviours as a function of the flow conditions. They show how the evolution from smooth to patchy to fully developed turbulent flow can be rationalized using a theoretical picture that takes into account the underlying nonlinearities intrinsic to fluid dynamics. Over a century of research into the origin of turbulence in wall-bounded shear flows has resulted in a puzzling picture in which turbulence appears in a variety of different states competing with laminar background flow 1 , 2 , 3 , 4 , 5 , 6 . At moderate flow speeds, turbulence is confined to localized patches; it is only at higher speeds that the entire flow becomes turbulent. The origin of the different states encountered during this transition, the front dynamics of the turbulent regions and the transformation to full turbulence have yet to be explained. By combining experiments, theory and computer simulations, here we uncover a bifurcation scenario that explains the transformation to fully turbulent pipe flow and describe the front dynamics of the different states encountered in the process. Key to resolving this problem is the interpretation of the flow as a bistable system with nonlinear propagation (advection) of turbulent fronts. These findings bridge the gap between our understanding of the onset of turbulence 7 and fully turbulent flows 8 , 9 .