Turbulence--Cloud Interactions: Laboratory and Field Studies

在我们对云的物理学的大部分研究中，一个基本的基本假设是，水滴在亚网格尺度上以完全随机的方式分布在空间中。现在人们已经认识到，这一假设在发生卷吸的云边明显违反了这一假设，但湍流对云内部液滴空间分布的影响，从而对我们对云物理过程的理解，直到最近才受到密切关注。理论和模型研究提出的湍流应该“聚集”水滴的说法，已被证明很难从云中观测中得到证实，这主要是因为现场设备的采样问题。由首席调查员进行的风洞实验似乎为该环境中的集群提供了一些支持。这笔赠款支持继续进行实验室研究，以调查在特征良好的条件下湍流对液滴空间分布的影响，特别强调这一点如何应用于碰撞-合并过程。原理研究人员将使用高空间分辨率、高数字分辨率和短曝光电荷耦合器件(CCD)相机，在实验室湍流室内使用在线全息术测量液滴的三维空间分布。湍流室将变得更大，以便里面的湍流雷诺数更接近于大气中的雷诺数，并且能量耗散率与大气中的相似。将用粒子图像测速仪来表征燃烧室内的流动。液滴的空间分布与湍流特性一起，可以研究液滴聚集与液滴大小和湍流强度的关系。进一步增加一台从德国马克斯·普朗克动力学和自组织研究所借来的高速数码相机，将允许测量液滴的相对速度分布，从而结束评估通用收集内核所需的测量。实验室结果将被评估，并扩展到自然云中的高湍流雷诺数区域，使用相同的直列全息系统。广泛的影响：这项工作具有广泛的潜在影响，因为它跨越大气科学和工程多相流领域。首席调查员与工程多相流领域的人有着密切的合作关系，因此受益于大气科学界，并作为多相流领域更多工程专业知识的渠道。这项实验工作是对一个理论和模型工作已经超过了我们的观测能力的领域的关键贡献。这位首席研究员在与本科生合作方面有着良好的记录，他希望继续获得这笔资助，并将支持一名研究生和一名博士后。

A basic underlying assumption for most of our treatment of the physics of clouds is that drops are distributed in space in a perfectly random manner at sub-grid scales. It has been recognized for some time now that this assumption is clearly violated at cloud edges where entrainment takes place, but the impact of turbulence on drop spatial distributions in cloud interiors, and hence on our understanding of cloud physical processes, has only recently come under intensive scrutiny. The suggestion from theoretical and modeling studies that turbulence should "cluster" drops has proven difficult to confirm from in-cloud observations, mostly because of sampling problems with in situ devices. Wind tunnel experiments performed by the principle investigator seem to provide some support for clustering in that environment. This grant supports continued laboratory studies to investigate the impact of turbulence on drop spatial distributions in well-characterized conditions, with particular emphasis on how this applies to the collision-coalescence process. The principle investigator will use high spatial resolution, high digital resolution, and short exposure Charge Coupled Device (CCD) cameras to make measurements of the three-dimensional spatial distribution of drops using inline holography in a laboratory turbulence chamber. The turbulence chamber will be larger such that the turbulence Reynolds number inside will be closer to and the energy dissipation rates similar to those found in the atmosphere. The flow inside the chamber will be characterized with particle image velocimetry. The spatial distribution of drops, together with the turbulence characterization, allows for investigations of the dependence of clustering on drop size and turbulent intensity. A further addition of a high speed digital camera, loaned from the Max Planck Institute for Dynamics and Self Organization in Germany, will allow measurement of the drop relative velocity distribution, thus closing the measurements needed to evaluate the generalized collection kernel. The laboratory results will be evaluated, and extended to high turbulence Reynolds number regimes, in natural clouds using the same inline holographic system.Broader Impacts: This work has broad potential impact as it spans the fields of atmospheric sciences and engineering multiphase flows. The principle investigator has strong collaborative ties with people in the engineering multiphase flow community, and thus benefits from and acts as a conduit to the atmospheric sciences community of the greater engineering expertise in multiphase flows. This experimental work is a critical contribution to a field where theoretical and modeling work has outpaced our observational abilities. The principle investigator has a well-established track record working with undergraduate students, which he hopes to continue with this grant, and will also support one graduate and one post-doctoral student.