Dynamics and symmetries of flow reversals in turbulent convection

TL;DR

This paper uses numerical simulations and symmetry analysis to understand flow reversals in turbulent convection, identifying key modes and invariances that characterize the reversal process.

Contribution

It introduces a Fourier mode-based framework and symmetry arguments to analyze flow reversals in Rayleigh-Bénard convection, linking flow structures to reversals.

Findings

Large-scale Fourier modes describe flow structures during reversals

Flow reversal involves the vanishing and rising of specific Fourier modes

Symmetry transformations identify reversing and non-reversing modes

Abstract

Based on direct numerical simulations and symmetry arguments, we show that the large-scale Fourier modes are useful tools to describe the flow structures and dynamics of flow reversals in Rayleigh-B\'enard convection (RBC). We observe that during the reversals, the amplitude of one of the large-scale modes vanishes, while another mode rises sharply, very similar to the "cessation-led" reversals observed earlier in experiments and numerical simulations. We find anomalous fluctuations in the Nusselt number during the reversals. Using the structures of the RBC equations in the Fourier space, we deduce two symmetry transformations that leave the equations invariant. These symmetry transformations help us in identifying the reversing and non-reversing Fourier modes.