Subcritical transition to turbulence: recent developments and the modern understanding
Nazmi Burak Budanur
Institute of Science and Technology Austria
Abstract: Turbulence in shear flows can take place in the absence of a linear instability of the base (laminar) flow. The nature of this transition remained a mystery for more than a century since the pioneering experiments of Osborne Reynolds. In the past three decades, this problem enjoyed several significant developments following the introduction of new ideas from the theories of nonequilibrium phase transitions and dynamical systems. In our current understanding, spatially-localized chaotic solutions of Navier-Stokes equations that govern the fluid motion emerge from finite-amplitude time-invariant solutions, which themselves appear in saddle-node bifurcations without a connection to the laminar flow. As the control parameter, the Reynolds number, of the system is increased the spatiotemporal dynamics of these chaotic spots lead to the sustenance of the turbulence and this transition falls into the directed percolation universality class. I will begin my talk with a historical overview of the transition problem and summarize the key recent developments. In the second half of the talk, I will present our recent analysis of the numerical solutions of pipe flow and how the geometry of state space ensures the presence of chaotic transients with a fractal basin boundary.
Yer : MSGSÜ Bomonti Binası, Fizik Bölümü
Tarih : 31 Mayıs 2018 Perşembe, 15.00