Collaborative Research: ABR: Multiscale Dynamics in Explosive Volcanic Eruptions

爆炸性火山喷发是地球上能量最大的颗粒流之一，其中最大的一次可能会对全球产生影响。即使是更常见的、较小的事件，也只有几公里的规模。然而，这些流动中的质量和能量转移从根本上由空间和时间尺度小得多的过程控制，在这些过程中，单个粒子相互作用，与气体或流动所经过的表面相互作用。我们过去在蒸汽爆炸、灰烬产生和热传递方面的工作表明，从实验发展而来的亚网格模型可以与大规模的数值模拟相耦合。更重要的是，这些次网格关系对于预测反映在火山沉积和火山灰扩散模式中的动态是至关重要的；忽略次网格过程的模型可能无法在火山沉积中产生几个数量级的能量转移。我们预测大规模火山流行为的能力最终可能会受到我们对非常小规模或微物理过程的理解的限制。在这项研究中，研究人员将在实验室中检查一套粒子尺度的质量和能量转移机制，目的是了解这些过程的物理原理，并将其纳入对火山爆发的大规模模拟中。该项目将支持正在进行的预测计算火山学方面的努力。具体地说，他们的团队将专注于1)高雷诺数下颗粒与气体之间的热传递，并使用碎屑冷却代理来检查火山碎屑密度流中的夹带，2)颗粒沉积和再悬浮，包括颗粒碰撞在形成沉积特征中的作用，3)气体-颗粒密度驱动流的大型实验，以及4)管道和火山碎屑密度流中细灰颗粒的产生。所有这些过程都有助于火山灰和更大的火山碎屑的产生和扩散，从而直接影响火山建筑物的环境，也有助于火山灰在大气中更广泛的扩散。了解这些过程的物理过程对于确定喷发的潜在航空、气候和局部危险至关重要。所有拟议的实验都将在与自然流动相似的材料和条件下进行，以最大限度地减少扩展到大规模多相流的潜在困难。在所提出的方法中，数值模型与实验数据有机地联系在一起。数值模式的优点是能够求解非线性、复杂耦合的方程并确定紧急行为，而实验的优点是详细了解在小尺度上运行的物理过程。

Explosive volcanic eruptions are some of the most energetic granular flows on the planet, the largest of which can have global impact. Even the more common, smaller, events encompass scales of several kilometers. However, mass and energy transfer in these flows are fundamentally controlled by processes at much smaller spatial and temporal scales, where individual particles interact with each other, with gas, or with the surface over which the flows travel. Our past work on steam explosions, ash production, and heat transfer have shown that subgrid models developed from experiments can be coupled to large-scale numerical simulations. More importantly, these subgrid relations are critical for predicting the dynamics reflected in volcanic deposits and in ash dispersal patterns; models that neglect subgrid processes can fail to produce the energy transfer manifest in volcanic deposits by several orders of magnitude. Our ability to predict large-scale behavior of volcanic flows can ultimately be limited by our understanding of very small-scale, or microphysical, processes. In this study, the investigators will examine a suite of particle-scale mass and energy transfer mechanisms in the laboratory with the aim of understanding the physics of these processes and to incorporate them into large-scale simulations of explosive volcanic eruptions. This project will support an ongoing effort in predictive computational volcanology. Specifically they team will focus on 1) heat transfer between particles and gas at high Reynolds numbers and using clast cooling proxies to examine entrainment in pyroclastic density currents, 2) particle deposition and resuspension, including the role of particle impacts in generating depositional features, 3) large-scale experiments of gas-particle density driven flows, and 4) and the production of fine ash particles in the conduit and in pyroclastic density currents. All these processes contribute to production and dispersal of ash and larger pyroclasts to the immediate environment of the volcanic edifice and also to the wider dispersal of ash in the atmosphere. Understanding the physics of these processes is crucial in determining the potential aviation, climactic, and local hazards of eruptions. All of the proposed experiments will be conducted with materials and at conditions similar to those in natural flows, minimizing the potential difficulties with scaling to large-scale multiphase flows. In the methodology proposed, the numerical models are integrally connected to the experimental data. The strength of numerical models is the ability to solve non-linear, complexly coupled equations and determine emergent behavior, and the strength of the experiments is to understand in detail the physical processes operating at small scales.