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Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions
Published on: February 22, 2018
Distinct large-scale turbulent-laminar states in transitional pipe flow
1Mathematics Institute, University of Warwick, Coventry, United Kingdom. D.C.Moxey@warwick.ac.uk
Summary
Researchers identified three distinct turbulent flow states in pipes, transitioning at specific Reynolds numbers. This reveals new insights into the complex dynamics of transitional turbulence and its inherent intermittent nature.
Area of Science:
- Fluid Dynamics
- Turbulence Research
- Nonlinear Dynamics
Background:
- Fluid flow exhibits laminar and turbulent motion.
- The transition between laminar and turbulent flow is a long-standing problem.
- The large-scale nature of transitional turbulence is less understood.
Purpose of the Study:
- Investigate the nature of transitional turbulence in pipe flow.
- Characterize different turbulent states and their transitions.
- Explore the underlying mechanisms of turbulence generation and propagation.
Main Methods:
- Extensive numerical computations in pipes of variable lengths (up to 125 diameters).
- Analysis of flow behavior across a range of Reynolds numbers.
- Comparison with directed percolation models.
Main Results:
- Identified three distinct turbulent states separated by two critical Reynolds numbers (Re(1) ≈ 2,300 and Re(2) ≈ 2,600).
- Below Re(1), turbulence exists as localized, equilibrium puffs.
- At Re(1), flow transitions to a spatio-temporally intermittent state filling the pipe, with turbulence fraction increasing until Re(2) leading to uniform turbulence.
Conclusions:
- Re(1) marks the onset of turbulence that persists indefinitely (infinite-lifetime turbulence).
- The intermittent turbulent state is an inherent property, not caused by random disturbances.
- Findings provide a new framework for understanding transitional turbulence, linking it to directed percolation theory.
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