Explore the fascinating journey towards understanding turbulence in this comprehensive colloquium talk. Delve into the complex world of subcritical shear flows, examining recent developments in experiments, simulations, and theory that establish a connection between transition in these flows and directed percolation. Learn about precise critical points for systems without linear instabilities and how to characterize the onset of turbulence using universal power laws. Discover the physics behind complex turbulent structures observed near transition and gain insights into outstanding questions in the field. The talk covers topics such as critical Reynolds numbers, wall-bounded shear flows, intermittent turbulence, statistical phase transitions, and the mechanism for localization in turbulent flows.
Overview
Syllabus
DATE: Thu, 20 February 2020, 14:30 to
The Route to Turbulence
Critical Reynolds numbers for onset of turbulence in a pipe
Observations by Reynolds 1883
Wall-Bounded Shear Flows
Finite-amplitude instability
Subcritical Transition Scenario
Subcritical Shear Flows
Intermittent Turbulence
Overview
Is turbulence in a pipe sustained at Re=1900
Statistical Phase Transitions
Tutorial on absorbing state transitionsDirected Percolation
Janssen-Grassberger
turbulence = disease
Wait a while
Turbulence Survival Lifetimes
Puffs can split Disease can spread
Splitting lifetimes
Laminar Flow and Turbulence
Generic behavior
Do any actual shear flows behave this way?
Can we do more?
Rc Turbulence fraction increases as R increases from Rc
Characteristic temporal scale: Characteristic spatial scale: $1
Critical scaling exponents
Puffs can split
Directed percolation phase transition to sustained turbulence in Collette flow
Universal continuous transition to turbulence in a planar shear flow
Why is there intermittenty?
Mechanism for localization Slug
Puff formation in long pipe
Puff and Slug
Excitable and Bistable
Transition scenario is captured by transition from Excitability to Bistability, together with fluctuations on the upper excited branch.
Brings tremendous clarity to transition in subcritical shear flows
This must be the "right way"
Intermittent vs Fully Turbulent
Q&A
Taught by
International Centre for Theoretical Sciences
