Dynamics of multiphase plumes in sheared stratified crossflows: implications for managing the environmental impacts of volcanic eruptions (Ref: 4659)

火山灰和气体云对人类生命、基础设施和飞机构成重大危害。了解火山羽流的高度、喷发强度（即其质量通量）和火山大气条件（如风速）之间的关系是管理喷发危机、重建过去的喷发动态和为未来的喷发做准备的关键。然而，喷发强度的估计可能不确定超过一个数量级，这破坏了我们对火山羽流动力学的理解。另一种方法是使用类似于火山羽流的小规模实验室实验，其中测量的不确定性很小，但其内在的限制是简化了真实羽流中发生的条件。例如，只有少数模拟实验解释了风对羽流动力学的强烈影响，而且所有这些实验都使用了均匀的横流，这严重破坏了它们与通常强烈垂直剪切的风廓线的类比。除了火山学之外，在基础流体动力学中很少有实验工作来研究剪切分层交叉流中多相羽流的动力学，尽管这种羽流在许多环境和工业问题中很常见。为了突破我们对火山羽流动力学的认识，本博士项目将结合三种方法：1)利用卫星观测，建立由火山伞状云生长速率导出的火山喷发强度数据库。结合新的独立火山爆发源参数档案（IVESPA）数据库，该数据库包含来自野外沉积物的喷发强度，这将产生一个前所未有的数据集，其中包含大量观测良好的火山事件，并且具有两个独立的强度约束。ii)将设计一个新的实验室实验，研究分层交叉流中上升的多相浮力羽流，并首次包括垂直剪切交叉流。带有硅酸盐砂颗粒的彩色盐水羽流将被注入具有盐度梯度的水箱中，以重现大气分层。一个不均匀的横流，通过一系列泵产生，以重现真实的大气风廓线。关键的状态参数将被缩放以匹配火山羽流发生的动力状态。羽流的宏观特性（例如，顶部高度和羽流宽度）将使用摄像机进行监测。iii)自然喷发(i)和实验室实验（ii）的观测结果将用于评估和开发各种复杂程度的数值火山羽流模型，范围从具有参数化湍流卷带的一维（1D）火山羽流模型到基于OpenFOAM计算流体动力学软件的三维火山羽流模型。

Volcanic ash and gas clouds pose significant hazards to human life, infrastructure, and aircraft. Understanding the relationship between the height of a volcanic plume, the intensity of an eruption (i.e. its mass flux) and atmospheric conditions (e.g. wind speed) at the volcano is key to managing eruptive crises, reconstructing past eruption dynamics, and preparing for future eruptions. However, estimates of eruption intensity can be uncertain by over an order of magnitude which undermines our understanding of volcanic plume dynamics.An alternative approach is to use small-scale laboratory experiments analogue to volcanic plumes in which measurement uncertainties are small, but an intrinsic limitation is the simplification of conditions occurring in real-world plumes. For example, only a handful of analogue experiments have accounted for the strong influences of wind on plume dynamics, and all of them used a uniform crossflow which critically undermines their analogy with wind profiles which are commonly strongly sheared vertically. Beyond volcanology, very little experimental work has been carried out in fundamental fluid dynamics to investigate the dynamics of multiphase plumes in sheared stratified crossflow, despite such plumes being common in many environmental and industrial problems.To make a breakthrough in our understanding of the dynamics of volcanic plumes, this doctoral project will aim to combine three approaches:i) Using satellite observations, a database of eruption intensity derived from the growth rate of volcanic umbrella cloud will be built. Combined with the novel Independent Volcanic Eruption Source Parameter Archive (IVESPA) database that contains eruption intensity derived from field deposit, this will result in an unprecedented dataset with large number of well-observed volcanic events with two independent constraints on intensity.ii) A novel laboratory experiment on multiphase buoyant plumes rising in a stratified crossflow will be designed and, for the first time, include vertically sheared crossflow. A coloured saltwater plume with silicate sand particles will be injected into a water tank with a salinity gradient to reproduce atmospheric stratification. A non-uniform crossflow, created via an array of pumps, to reproduce realistic atmospheric wind profiles. Key regime parameters will be scaled to match the dynamical regimes in which volcanic plumes occur. The macroscopic properties of the plume (e.g., top height and plume width) will be monitored using video cameras.iii) The observations from natural eruptions (i) and laboratory experiments (ii) will be used to evaluate and develop numerical volcanic plume models of various complexity, ranging from one-dimensional (1D) plume models with parameterized turbulent entrainment to 3D volcanic plume models based on the OpenFOAM computational fluid dynamics software.