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Possible universal transitional scenario in a flat plate boundary layer: measurement and visualization
Lee1
1Laboratory of Fluid Mechanics, Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China and State Key Laboratory for Turbulence Research (SKLTR), Peking University, Beijing 100871, China.
Summary
This study reveals that turbulence onset in boundary layers occurs later than previously thought, following the breakdown of long streaks, not initial wave or vortex breakdown. An alternative transitional scenario was developed.
Area of Science:
- Fluid dynamics
- Aerodynamics
- Turbulence research
Background:
- Understanding the transition from laminar to turbulent flow is crucial in fluid dynamics.
- Previous models suggested turbulence onset immediately follows boundary layer breakdown.
Purpose of the Study:
- To investigate the characteristic flow structure during nonlinear boundary layer instability and the onset of turbulence.
- To challenge existing transitional scenarios and propose an alternative model.
Main Methods:
- Experimental investigation using a controlled Tollmien-Schlichting wave in a 2D boundary layer.
- Employed hot-film measurements and hydrogen bubble visualization techniques.
- Analyzed the growth and evolution of controlled disturbances.
Main Results:
- Laminar boundary layer breakdown and Lambda vortex breakdown do not directly cause immediate turbulence onset.
- Turbulence onset was observed to occur later, linked to the breakdown of long streaks.
- An alternative scenario for the transition process was developed based on experimental findings.
Conclusions:
- The study refines the understanding of turbulence transition in boundary layers.
- Highlights the critical role of streak breakdown in initiating turbulence.
- Provides a new framework for analyzing laminar-turbulent transition.