Rayleigh Number Effects on Direct Numerical Simulations of the “Pi Chamber"

The Pi Chamber is an aerosol-cloud chamber at Michigan Technological University which has the capability to generate steady-state cloud formation through moist turbulent Rayleigh-Benard flow between saturated, temperature controlled top and bottom plates. This capability allows for study of various interconnecting processes such as clouds, aerosols, water vapor, trace gases, thermodynamics, and turbulence. These capabilities make it a powerful tool for study of cloud microphysics. Despite great experimental capabilities, there are limitations in the capture of data that can be helpful for understanding of cloud microphysics. To assist the Pi Chamber, a direct numerical simulation was developed with the focus on providing Lagrangian droplet statistics and three-dimensional, time-resolved data on fluid flow over the entire domain. In a previous study, the model matched the salient features of the Pi Chamber experiments and proved to be a valuable tool in understanding cloud microphysics in this context. However, the numerical model did not match the Rayleigh number of the Pi Chamber experiments because of computational limits. The previous study conducted simulations with Ra = 7.9 ∗ 10^6 while that of the experiments is generally ≥ 10^9. Because coupling of turbulence and cloud microphysics is a primary motivation in the development of the Pi Chamber, it is important to determine what effect the Rayleigh number has on cloud microphysics in the simulation. In this study, the Rayleigh number in the simulation is scaled up to match that of the Pi Chamber experiments. The goal is simply to examine how the flow and cloud microphysics change as Rayleigh number increases. From these observations, comments on the coupling of turbulence and cloud microphysics in this context can be made and the simulation’s ability to be paired with the Pi Chamber experiments for further understanding can be evaluated.