Precursor for wind reversal in a square Rayleigh-Bénard cell.

Area of Science:

• Fluid Dynamics
• Convective Heat Transfer
• Computational Physics

Background:

• Rayleigh-Bénard convection is a fundamental system for studying fluid instabilities.
• Large-scale circulation reversals are complex phenomena observed in turbulent convection.
• Proper Orthogonal Decomposition (POD) is a powerful tool for reducing the dimensionality of complex systems.

Purpose of the Study:

• To investigate the dynamics of large-scale circulation reversals in a 2D Rayleigh-Bénard cell.
• To validate a five-mode POD-based model against simulation data.
• To identify and understand the role of precursor events in circulation reversals.

Main Methods:

• Utilized a five-mode proper orthogonal decomposition (POD)-based model.
• Simulated Rayleigh-Bénard convection at Ra=5×10⁷ and Pr=4.3.
• Analyzed the behavior of POD modes, particularly mode L*.

Main Results:

• The five-mode model accurately predicts the behavior of POD modes, including the critical mode L*.
• Mode L* was identified as a precursor event, disconnecting core and boundary layers before reversal.
• The model successfully reproduces observed reversal dynamics and time scales when intermittency is included.

Conclusions:

• Mode L* is instrumental for circulation reversal dynamics in the model and likely in simulations.
• Circulation reversals are characterized by three distinct time scales: transition, inter-reversal, and precursor durations.
• Incorporating noise to account for small-scale intermittency improves model agreement with simulation results.