Turbulent superstructures in Rayleigh-Bénard convection

Area of Science:

• Fluid dynamics
• Turbulence research
• Convection phenomena

Background:

• Turbulent Rayleigh-Bénard convection can exhibit large-scale order (superstructures) like rolls and cells.
• These patterns resemble those observed near the onset of convection, despite high turbulence levels.

Purpose of the Study:

• To investigate the characteristic scales and dynamics of turbulent superstructures.
• To explore the relationship between superstructures, fluid properties (Prandtl and Rayleigh numbers), and boundary layer behavior.
• To determine if a simplified description of turbulent superstructures is possible for geophysical and astrophysical applications.

Main Methods:

• Numerical simulations of turbulent convection.
• Varying Prandtl numbers (0.005 to 70) and Rayleigh numbers (up to 10^7).
• Analysis of temperature and velocity fluctuations to identify large-scale patterns.

Main Results:

• Identified characteristic scales and times separating small-scale turbulent fluctuations from large-scale superstructures.
• Observed that superstructure scales depend on Prandtl and Rayleigh numbers.
• Correlated superstructure dynamics with boundary layer phenomena, specifically thermal plume clustering.

Conclusions:

• Scale separation exists between turbulent fluctuations and large-scale superstructures.
• The findings suggest a simplified model for turbulent superstructures is feasible.
• This has implications for understanding phenomena in geophysical and astrophysical settings.