Particle clustering in dilute pyroclastic density currents and plumes

火山碎屑密度流是由火山爆发产生的固体颗粒和气体的高温和快速移动的混合物。它们在陆地表面上旅行很长的距离，长达数十公里，造成重大危害，并改变景观。在大气层中蔓延的火山羽流将爆炸性喷发的颗粒输送到更远的地方，甚至数百公里。在这些爆炸性喷发中形成颗粒群是一个关键过程，因为颗粒群影响颗粒的浓度，从而影响流动的速度和它们行进的距离。然而，聚类仍然是一个知之甚少的过程。通过量化控制聚类，它是可能的，以限制地球物理湍流气粒混合物，这是必不可少的理解流动动力学的颗粒浓度。火山碎屑密度流是所有火山灾害中最具破坏性的，部分原因是它们在地面上传播，速度很快。火山羽流对社区和航空业构成重大危险，因为它们可以将火山灰散布到很远的地方。结果将提供新的洞察颗粒浓度，从而流速，动压，沉降速率和危害。这些实验将在火山学领域之外具有相关性，因为湍流颗粒流在自然界和工业过程中都很常见，如雪崩和化学反应堆。这项研究工作为学生提供了多学科培训机会，并使学术和政府组织之间能够进行合作，实验室实验将用于确定对群集的控制以及对火山粒子流的影响。火山颗粒流中颗粒的浓度控制着流动密度，从而控制着流动速度、行进距离和危险性。在稀释的湍流扩散羽流和火山碎屑密度流中，颗粒浓度由沉降控制，而沉降又由颗粒与周围气体以及颗粒之间的相互作用控制。控制稀流中颗粒沉降和浓度的一个关键过程是颗粒的聚集，其中形成了较高浓度的区域，但尚未得到很好的表征。 实验装置将被设计为允许大量的实验，从而探索参数和过程之间的关系，包括粒度和粒度分布的作用。一种新的声学传感方法将被开发和测试，以测量颗粒浓度。实验结果将被用来解释存款从历史喷发，以确定何时以及如何集群影响喷发动力学和喷发粒子的分散。集群的定量描述将提高与现场存款的动态这些电流的能力。实验结果可用于改进火山碎屑灾害模型。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。

Pyroclastic density currents are hot and fast-moving mixtures of solid particles and gas produced by explosive volcanic eruptions. They travel great distances over the land surface, up to many tens of kilometers, pose substantial hazards, and alter landscapes. Spreading volcanic plumes in the atmosphere transport particles from explosive eruptions to even greater distances, many hundreds of kilometers. The formation of clusters of particles in these explosive eruptions is a critical process because clusters affect the concentration of particles and thus the speed of the flows and the distance they travel. Clustering, however, remains a poorly understood process. By quantifying the controls on clustering, it is possible to constrain particle concentration in geophysical turbulent gas-particle mixtures which is essential for understanding flow dynamics. Pyroclastic density currents are the most devastating of all volcanic hazards, in part because they propagate over the ground surface and with great speed. Volcanic plumes present substantial hazards to communities and aviation as they can disperse ash over great distances. Results will provide new insight into particle concentration and hence flow speed, dynamic pressure, sedimentation rates, and hazard. The experiments will have relevance outside the field of volcanology because turbulent particle-laden flows are common in both nature and industrial processes such as snow avalanches and chemical reactors. The research effort provides multidisciplinary training opportunities for students and enables collaboration between academic and government organizations.Laboratory experiments will be used to identify the controls on clustering and the implications for volcanic particle-laden flows. The concentration of particles in volcanic particle-laden flows controls the flow density and hence flow velocity, distance travelled, and hazard. In dilute, turbulent spreading plumes and pyroclastic density currents, particle concentration is controlled by sedimentation which in turn is controlled by how particles interact with the surrounding gas and with each other. A critical, but not well characterized, process controlling particle sedimentation and concentration in dilute flows is the clustering of particles, in which zones of higher concentration develop. The experimental setup will be designed to permit a large number of experiments and hence to explore relationships between parameters and processes including the role of particle size and size distribution. A novel acoustic sensing method will be developed and tested to measure particle concentration. The experimental results will be used to interpret the deposits from historical eruptions to identify when and how clustering affects eruption dynamics and the dispersal of erupted particles. A quantitative description of clustering will improve the ability to relate field deposits to the dynamics of these currents. The experimental results can be used to improve models for pyroclastic hazards.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.