A priori testing of subgrid-scale models for large eddy simulations in supersaturated conditions

Abstract

Turbulence is characterized by irregular movement in pressure and flow velocity. Better understanding of turbulent flow will help in the understanding of air movement including wind currents, dissipation of pollutants and storm formation. Although much research has been done on the nature of turbulence in the atmosphere, less work has been focused on humidity turbulence in supersaturated conditions. Supersaturation turbulence is found in clouds and plays a major role in the formation of precipitation. In an effort to better understand LES and the closure problem for turbulence fluctuations of supersaturation, temperature was monitored within a cloud chamber while turbulence was being induced. Several measurements were made with a thermistor array at various temperature differences and spacings. The data gathered was used for a priori testing. Two models, a scale-similarity model and a Gradient model, were tested with the data gathered. The scale-similarity showed to be very promising with correlation coefficients around 0.7. The Gradient model had correlation coefficients around 0.2. Although one of the models performed slightly better at the smallest horizontal spacing, there didn’t appear to be any significant patterns between horizontal spacing or temperature difference and how well the models performed. A posteriori tests will need to be performed in the future to better test how well the scale-similarity model behaves in various circumstances. Supersaturation LES models will further scientists’ understanding of the humidity turbulence present during the formation of clouds and precipitation.