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Updated: Feb 28, 2026
11:51
Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions
Published on: February 22, 2018
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Transitional-turbulent spots and turbulent-turbulent spots in boundary layers
Xiaohua Wu1, Parviz Moin2, James M Wallace3
1Department of Mechanical and Aerospace Engineering, Royal Military College of Canada, Kingston, ON, Canada K7K 7B4.
Summary
Bypass transition involves hairpin packets, not streak breakdown. Turbulent-turbulent spots, concentrated vortices, emerge in turbulent boundary layers, impacting streaks and increasing stress.
Area of Science:
- Fluid dynamics
- Turbulence research
- Boundary layer theory
Background:
- Bypass transition is a key phenomenon in fluid dynamics.
- Understanding turbulent boundary layers is crucial for many engineering applications.
- Previous models of transition did not fully capture spot inception mechanisms.
Purpose of the Study:
- To investigate the mechanisms of transitional-turbulent spot inception.
- To identify and characterize novel turbulent structures within developed turbulent boundary layers.
- To elucidate the interaction between turbulent structures and near-wall streaks.
Main Methods:
- Direct numerical simulation (DNS) of a canonical boundary layer.
- Analysis of flow structures, including vortex dynamics and streak behavior.
- Systematic investigation of turbulent spot characteristics and their generation.
Main Results:
- Transitional-turbulent spot inception is analogous to secondary instability, forming hairpin packets.
- Streak meandering and breakdown facilitate spot spreading, not inception.
- Discovery of 'turbulent-turbulent spots' in the inner layer of turbulent boundary layers.
- These spots are concentrated vortices originating from hairpin packets, impacting viscous sublayer streaks.
- Turbulent-turbulent spots correlate with high Reynolds shear stress, enstrophy, and temperature fluctuations.
Conclusions:
- The inception mechanism for bypass transition differs from previous assumptions.
- Turbulent-turbulent spots represent a newly identified turbulent structure with significant near-wall effects.
- Viscous sublayer streaks appear to be passive structures influenced by turbulent-turbulent spots.
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