EAGER: A Vertical Wind Tunnel for Determination of Scavenging Efficacy and Hydrometeor Physics

雨滴在云下的清除在从大气中清除导致气候变化的自然和人为气溶胶方面发挥着关键作用。然而，清除气溶胶的降雨事件仍然是气候模式中最不确定的组成部分，主要是由于目前的实验限制，提供直接证据的气溶胶收集下降的雨滴。该项目将建造一个垂直风洞，能够悬浮水滴，同时将水滴暴露于各种气溶胶类型。集成到风洞中的将是现代气溶胶生成和表征设备，允许精确地将气溶胶输送到液滴中。实验设施将有能力测量气溶胶收集的规定大小的一滴气溶胶的大小范围很大，而下降驻留在隧道。该实验设施将通过控制温度和湿度为水滴提供与大气相关的流动条件，并在平静和湍流的风条件下使水滴漂浮。高速摄像机将捕捉模拟自由落体中水滴的形状和振荡，因为水滴收集颗粒，生长和蒸发。建立这样一个设施将促进美国大气科学家与国际社会之间的更大合作，未来的学生交流，并成为STEM推广到当地高中生的平台。建立一个能够直接清除测量的Z型垂直风洞将改变大气科学家在雨滴和清除物理学方面的基本实验工作。很少有问题对大气科学具有重要意义，而且像气溶胶清除一样缺乏约束。该项目旨在创建一个能够解决撞击清除长期存在的问题的设施，特别是对于格林菲尔德间隙内的颗粒。单分散和多分散气溶胶将被输送到悬浮在鞘流中的液滴，由上游层压机产生。通过在液滴上游放置小物体将引入湍流。液滴内部和外部的流动将通过粒子的激光照明和高速相机来可视化。落物物理验证实验将与项目开始时在美因茨垂直风洞进行的实验进行比较，并将扫气验证数据与文献中现有的有限数据进行比较。垂直风洞提供了研究一些其他大气问题的能力，这些问题涉及自由落体中的化学物质吸收、雪花和沙粒的融化、霜化以及液滴的聚结和分裂。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Below-cloud scavenging by raindrops plays a critical role in removing natural and anthropogenic aerosols, those which contribute to climate change, from the atmosphere. However, scavenging of aerosols by rainfall events remains the most uncertain constituent in climate models, largely due to current experimental limitations to provide direct evidence of aerosol collection by falling raindrops. This project will construct a vertical wind tunnel capable of levitating water drops while exposing the drops to a wide range of aerosol types. Integrated into the wind tunnel will be modern aerosol generation and characterization equipment that permits the precise delivery of aerosols to the drop. The experimental facility will have the ability of measuring aerosol collection by a drop of prescribed size for a large range of aerosol sizes, while the drop resides in the tunnel. The experimental facility will deliver atmospherically relevant flow conditions to the drop by controlling temperature and humidity, and levitate drops in calm and turbulent wind conditions. High-speed cameras will capture the shape and oscillation of drops in simulated free fall as drops collect particles, grow, and evaporate. The establishment of such a facility will foster greater cooperation between US-based atmospheric scientists and the international community, the future exchange of students, and be a platform for STEM outreach to local high school students. Building a Z-type vertical wind tunnel capable of direct scavenging measurements will transform how atmospheric scientists approach fundamental experimental efforts in raindrop and scavenging physics. There are very few problems of the importance to atmospheric science and as poorly constrained as aerosol scavenging. This project is an effort to create a facility that can unravel longstanding questions in impaction scavenging, particularly for particles within the Greenfield Gap. Mono- and polydisperse aerosols will be delivered to drops levitating in sheath flow, created by upstream laminarizers. Turbulence will be introduced by placing small bodies upstream of the drop. Flow internal and external to the drop will be visualized by laser illumination of particles and high-speed cameras. Validation experiments of drop physics will be compared with those performed at the Mainz vertical wind tunnel at project inception, and scavenging validation data compared to measurements garnered from existing, limited data in literature. A vertical wind tunnel provides the ability to study a number of other atmospheric problems dealing with falling objects such as chemical species absorption in free fall, melting of snowflakes and graupels, riming, and drop coalescence and breakup.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.