The Interaction of Pyroclastic Density Currents with the Atmosphere & Landscapes: Integrating Experiments and Computational Approaches for Validation & Examination of Entra

火山碎屑密度流（PDCs）是最危险和不可预测的火山现象之一。这些洋流威胁着全世界2亿多人。当爆炸性喷发物质的混合物密度大于大气时，就会产生这种电流，其特点是高速和高温，对人和基础设施特别危险。然而，由于难以预测这些洋流的发生、危险的条件和不透明限制了对内部动力学的观察，对这些洋流内部工作的直接观察受到了干扰。这些电流通常在单个电流中具有不均匀的粒子浓度，因此单个事件将具有一系列时空演变和重叠的物理过程。最终，这些电流是由电流和大气之间的密度对比驱动的，任何改变电流颗粒浓度的过程（如空气夹带或基材的侵蚀）都将显著影响它们的动力学。通过这种方式，PDC对其所经过的大气和景观敏感并与之交流。然而，关于PDC的夹带和侵蚀的知识存在明显的差距。建议的工作将进行大规模实验和数值模拟，以确定PDC内部物理过程。这些信息将用于改进我们的数值模拟工具，以更好地了解这些流的危害。这项工作将整合几种类型的实验结果，强调末端构件过程和尺度对PDC动力学的重要性。部分实验结果将用于验证这些过程的数值模拟，而其他实验将探索PDC中两个重要的物理过程：夹带和侵蚀。我们将解决以下相互关联的目标：2.验证流体动力学模型，以涵盖在不断变化的PDC中所经历的颗粒浓度和流体动力学环境。确定PDC的携砂效率，并将其与热演化和输运能力联系起来；3 .评估夹带产生自流化的能力。评估来自颗粒和气体源的床力，并将其与侵蚀能力联系起来。5 .生成可纳入任何数值方法的夹带和侵蚀模块，特别强调快速的端元模型，以帮助进行危害评估；制定“PDC流体动力学”视频/课程计划，突出实验和模拟的可视化，以教育学生PDC流体动力学的范围。

Pyroclastic density currents (PDCs) are among the most dangerous and unpredictable volcanic phenomena. These currents threaten over 200 million people worldwide. The currents are generated when mixtures of explosively erupted material are greater density than the atmosphere and are characterized by high velocities and temperatures making them particularly dangerous for people and infrastructure. Yet direct observation of the internal workings of these currents have been confounded by the difficulty in predicting their occurrence, hazardous conditions, and opacity limiting observation of the internal dynamics. These currents often have heterogeneous particle concentrations in a single current, so that a solitary event will have a range of spatial-temporally evolving and overlapping physical processes. Ultimately these currents are driven by the density contrast between the current and the atmosphere, and any process (such as air entrainment or erosion of the substrate) that changes the particle concentration of the current will significantly impact their dynamics. In this way, PDC are sensitive to and communicate with the atmosphere and landscape through which they travel. However, there is a distinct gap in knowledge concerning entrainment and erosion in PDC. The proposed work will conduct large-scale experiments and numerical simulations to determine internal physical processes in PDC. This information will be used to improve our numerical simulation tools to better understand the hazards from these flows.This proposed work will integrate the results of several styles of experiments that emphasize end member processes and scales important for PDC dynamics. Select experimental results will be used to validate the numerical simulation of these processes, while other experiments will explore two important physical processes in PDC, entrainment and erosion. We will address the following inter-related goals: 1. Validate fluid dynamics models to encompass the particle concentration and fluid dynamics environment experienced throughout an evolving PDC, 2. Determine the entrainment efficiency of PDC and relate this to thermal evolution and transport capacity, 3. Assess the ability of entrainment to generate self-fluidization, 4. Assess bed forces from both particle and gas sources and relate these to the erosive capacity, 5. Generate modules for entrainment and erosion that can be incorporated into any numerical approach with a particular emphasis on rapid, end-member models to aid in hazard assessment, and 6. Develop a "Fluid Dynamics of PDC" video/lesson plan that highlights the visualizations from both experiments and simulations to educate students on the range of fluid dynamics in PDC.