Modelling the Mixing and Erosion at the Head of Gravity Currents

模拟重力流头部的混合和侵蚀

基本信息

批准号：
EP/X028577/1
负责人：
Edward Skevington
金额：
$ 41.37万
依托单位：
University of Hull
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2023
资助国家：
英国
起止时间：
2023 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FX028577%2F1
关键词：
Modelling Mixing Erosion Head Gravity

项目摘要

Fluid movement driven by a density difference is very common. When a freezer is opened, or a window on a winter's day (a ventilation flow), you may have noticed that the dense, cold air rushes across your feet. This effect can be felt even if you are on the other side of the room, the cold air warming a little as it mixes with the warmer air above, but remaining sufficiently cool and distinct as it flows like a flood across the floor.These are part of a very broad family of fluid flows present across our homes, industries, and the wider environment, known as gravity-currents. Ventilation flows are important to understand for the spread of pathogens and disease, and cold-fronts are essentially the same but on the scale of 100-1000km. In industry, accidental spills of hazardous gas must be planned for, and suitable defences put in place. A very dangerous subset of gravity-currents are particle-driven currents, the suspended particle load providing the driving density and facilitating immense destructive power. For example, powder-snow avalanches are a hazard in mountainous regions, easily burying people and buildings. Pyroclastic density currents, searing hot clouds of ash released by volcanos and flowing out across the ground, famously buried Pompeii, leaving a city of people entombed in volcanic rock. Massive submarine turbidity-currents, >1000km long and moving at up to 10m/s, carry nutrients and carbon into the deep ocean, and have destroyed numerous cables and pipes carrying internet data or energy. Smaller (though still substantial) turbidity-currents will pose an increasing hazard to the UK as we develop deep-marine wind power, which must be connected back to shore by cables. The feasibility of these and other developments rely on our ability to predict and mitigate natural hazards. The front the current pushes aside the ambient fluid, and it is the dynamics here which determine the rate of advance of the current. In addition, this region is a principal source of mixing, and for some currents it is also a region in which there is intense erosion of the bed. As the current mixes with the fluid around it, it becomes more dilute, and the current becomes bigger while simultaneously having a reduced driving density. Conversely, as it erodes the bed the driving density increases. Thus, the front exerts a very strong control on the advance of the current, and the mixing and erosional processes are a critical part of this. However, to date these processes have not been included in the mathematical models that are designed to predict these currents, which has limited their applicability to flows over short distances so that the mixing does not substantially affect on the overall density. Additionally, the front of the current is the most dangerous part: the same processes that enable the rapid erosion of the bed can facilitate immense destructive power.In this fundamental scientific study, I will develop novel mathematical models that capture the dynamics of the front of a gravity-current, including the mixing and erosional processes. First, experimental work using newly developed techniques will yield data of unprecedented quality for a cool, temperature driven current, measuring the details of the vortices and mixing in both the head of the current and throughout. Additional experiments will focus on capturing the details of the erosional processes in sediment-driven currents. Informed by these measurements, I will capture the vital aspects of the dynamics of the head within a new mathematical model, for the first time including the mixing and erosional processes. Finally, the model of the head will be combined with a model for the rest of the current, which I developed previously, to give a complete model that can predict the motion of the current. This urgently required project represents a substantial leap-forward in our understanding and predictive power for this important and dangerous class of flows.

由密度差驱动的流体运动很常见。当冰箱打开，或者冬天打开窗户（通风）时，您可能会注意到浓密的冷空气从您的脚上流过。即使您在房间的另一侧，也可以感受到这种效果，冷空气与上面的暖空气混合时会稍微变暖，但当它像洪水一样流过地板时，仍然保持足够的凉爽和清晰。这些是它是我们的家庭、工业和更广泛的环境中广泛存在的流体流动家族的一部分，称为重力流。通风流对于了解病原体和疾病的传播非常重要，冷锋本质上是相同的，但规模为 100-1000 公里。在工业中，必须针对危险气体的意外泄漏做好计划，并采取适当的防御措施。重力流的一个非常危险的子集是粒子驱动流，悬浮粒子负载提供驱动密度并促进巨大的破坏力。例如，粉雪雪崩是山区的一种危险，很容易掩埋人员和建筑物。火山碎屑密度流，火山释放出的灼热火山灰云流过地面，著名的埋葬了庞贝古城，留下了一座被火山岩埋葬的城市。巨大的海底浊流长度超过 1000 公里，移动速度高达 10 m/s，将营养物质和碳带入深海，并摧毁了许多承载互联网数据或能源的电缆和管道。随着我们开发深海风力发电，较小的（尽管仍然很大）浊流将对英国造成越来越大的危害，而这些风力发电必须通过电缆连接回岸上。这些和其他发展的可行性取决于我们预测和减轻自然灾害的能力。水流的前端将周围的流体推开，这里的动力学决定了水流的前进速率。此外，该区域是混合的主要来源，对于某些洋流来说，它也是河床强烈侵蚀的区域。当电流与周围的流体混合时，它变得更加稀薄，电流变得更大，同时驱动密度降低。相反，当它侵蚀床层时，驱动密度就会增加。因此，锋面对水流的前进具有很强的控制作用，而混合和侵蚀过程是其中的关键部分。然而，迄今为止，这些过程尚未包含在旨在预测这些电流的数学模型中，这限制了它们对短距离流动的适用性，因此混合不会对整体密度产生实质性影响。此外，洋流的前端是最危险的部分：使河床快速侵蚀的相同过程可以产生巨大的破坏力。在这项基础科学研究中，我将开发新颖的数学模型来捕捉洋流前端的动态。重力流，包括混合和侵蚀过程。首先，使用新开发的技术进行的实验工作将产生前所未有的质量数据，用于冷却、温度驱动的电流，测量涡流的细节以及电流头部和整个电流的混合。其他实验将侧重于捕获沉积物驱动的水流中侵蚀过程的细节。根据这些测量结果，我将在一个新的数学模型中捕获头部动力学的重要方面，首次包括混合和侵蚀过程。最后，头部模型将与我之前开发的电流其余部分的模型相结合，得到一个可以预测电流运动的完整模型。这个迫切需要的项目代表了我们对这一重要而危险的流动类别的理解和预测能力的重大飞跃。