How is turbulence born: Spatiotemporal complexity and universality class of transitional fluids
Hong-Yan Shih1*
1Institute of Physics, Academia Sinica, Taipei, Taiwan
* Presenter:Hong-Yan Shih,
Turbulence is ubiquitous in daily life and causes damages and energy loss, but how a laminar flow becomes turbulent still has remained unsolved for 130 years. Recently precise measurements in pipe flow experiments finally quantified this transition, showing that spatiotemporal complexity develops through decay and splitting of localized turbulent puffs, whose mean lifetime and splitting time grow faster than exponentially but do not diverge as expected for typical phase transition. From numerical simulations of hydrodynamics equations, we discovered an emergent predator-prey dynamics at the onset of turbulence, through which we developed an effective Landau theory that reproduces the same statistics at transition, showing that the laminar-turbulent transition is indeed a non-equilibrium phase transition in the directed percolation universality class. Our work provides a unified picture of the transition to turbulence emerging in systems ranging from turbulent convection to magnetohydrodynamics.

Keywords: phase transition, non-equilibrium statistical mechanics, universality class, directed percolation, turbulence