Colloquium
Department of Physics, NCU
The emergence of collective modes, ecological collapse and universality class at the laminar-turbulent transition
Dr. Shih, Hong-Yan (施宏燕)
Institute of Physics, Academia Sinica (中央研究院物理研究所)
Date 2020.12.29 (Tue)
Place S4-625
Time 14:00-16:00
Abstract: How a laminar flow becomes turbulence has been an unsolved problem for more than a century and is important in various industrial applications. Recently precise measurements in pipe flow experiments showed non-trivial spatiotemporal complexity at the onset of turbulence where lifetime and splitting time of metastable turbulence do not diverge asymptotically as would have been expected in a sharp transition. Based on numerical evidence from the hydrodynamics equations, we discovered the surprising fact that the fluid behavior at the transition is governed by the emergent predator-prey dynamics of the important long-wavelength mode, leading to the mathematical prediction that the laminar-turbulent transition is analogous to an ecosystem on the edge of extinction. This prediction demonstrates that the laminar-turbulent transition is a non-equilibrium phase transition in the directed percolation universality class, and provides a unified picture of transition to turbulence emerging in systems ranging from turbulent convection to magnetohydrodynamics. I will also review recent progress about transitional turbulence.