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

该基金支持旨在模拟对流云的生长及其与周围空气相互作用的实验室实验。 大气中的云和普通实验室射流之间的一个主要区别是，在不断增长的云中发生的冷凝是一个稳定的热源和浮力。 在实验中，冷凝是通过一个电网来模拟的，当射流在水箱中上升时，电网会加热射流。 激光诱导荧光（LIF）用于流动显示和粒子图像测速（PIV）用于测量射流的速度场。 利用热致变色液晶实现了全场温度测量。 这项研究的部分动机是早期的结果，使用流动可视化，显示加热的效果是减少周围的流体夹带到射流的量。 这与直觉相反，但可以解释为什么自然云不会像实验室喷射那样随着高度的增加而迅速膨胀。 与荷兰德尔夫特理工大学的研究人员合作完成的湍流射流的直接数值模拟（DNS）补充了实验工作。 这项工作的目标是实现一个更好的物理理解的混合过程中发生的云边界。

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.