Observation of a link between energy dissipation rate and oscillation frequency of the large-scale circulation in dry and moist Rayleigh-Bénard turbulence

In this study both the small- and large-scale flow properties of turbulent Rayleigh-Bénard convection are investigated. Experiments are carried out using the Π chamber (aspect ratio Γ=2) for Rayleigh number range Ra∼108-109 and Prandtl number Pr≈0.7. Furthermore, experiments are run for dry and wet conditions, i.e., top and bottom surfaces of the chamber are dry and wet, respectively. For wet conditions we further distinguish between conditions with and without the presence of sodium chloride aerosol particles which, if supersaturated conditions are achieved, lead to cloud droplet formation. We therefore refer to these conditions as moist and cloudy, respectively. We see that the addition of water vapor influences the turbulent flow. In all cases, the turbulent kinetic energy dissipation rates increase with increasing temperature difference, but the slopes are different for wet and dry convection. We do not observe a clear difference between moist and cloudy convection due to low liquid water content. A similar lack of collapse with Ra is observed for the characteristic oscillations of the large-scale circulation. We observe that the first normalized characteristic oscillation frequency increased with increasing temperature difference, i.e., increasing Ra, for all conditions considered, but the slopes are different for wet and dry convection with again no clear difference between moist and cloudy convection. It turns out that the sloshing or torsional mode of the large-scale circulation and the turbulent flow or energy dissipation rate seem to be influenced by the same mechanism additional to the effect of buoyancy alone. These observational results provide supporting evidence that the large-scale circulation is insensitive to phase composition or interfacial physics and rather depends only on the strength of the turbulence.