Large-scale velocity structures in turbulent thermal convection

Area of Science:

• Fluid Dynamics
• Turbulent Convection

Background:

• Turbulent thermal convection is a fundamental process in nature and engineering.
• Understanding large-scale structures in turbulent convection is crucial for various applications.

Purpose of the Study:

• To systematically study large-scale velocity structures in turbulent thermal convection.
• To identify the driving mechanism for coherent rotation in these flows.

Main Methods:

• Experiments were conducted in three aspect-ratio cells filled with water.
• Laser Doppler velocimetry was employed to measure velocity profiles and statistics.
• Measurements were taken across varying Rayleigh numbers (Ra) and spatial positions.

Main Results:

• Large velocity fluctuations were observed in both central and boundary regions.
• A quasi-two-dimensional, coherent, rotating single-roll structure was identified.
• This structure scales with Ra and exhibits three distinct regions: viscous boundary layer, mixed core, and buffer region.

Conclusions:

• A unique driving mechanism for large-scale coherent rotation in turbulent convection was discovered.
• The identified structure provides a framework for understanding turbulent convection dynamics.
• The findings contribute to the fundamental knowledge of fluid dynamics in convective systems.