A Laboratory Analogue for Cloud Entrainment: Experiments and Simulations of Volumetrically Heated Jets

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This grant supports laboratory experiments designed to simulate the growth of convective clouds and their interaction with the air surrounding them. A major distinction between clouds in the atmosphere and ordinary laboratory jets is that the condensation occurring in a growing cloud is a steady source of heat and buoyancy. In the experiments, condensation is simulated by an electrical grid that heats a jet as it ascends in a water tank. Laser-induced fluorescence (LIF) is employed for flow visualization and particle image velocimetry (PIV) for measuring the velocity field of the jet. Whole-field temperature measurement (WFT) is achieved by using thermochromic liquid crystals. The study is motivated in part by earlier results using flow visualization that showed the effect of heating was to reduce the amount of ambient fluid entrained into the jet. This is contrary to intuition, but may explain why natural clouds do not expand with increasing height as rapidly as laboratory jets. The experimental work is complemented by direct numerical simulation (DNS) of turbulent jets, done in collaboration with researchers at Delft University of Technology in The Netherlands. The goal of the work is to achieve a better physical understanding of the mixing processes that occur at cloud boundaries.