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非常普遍。当冰箱打开或在冬季（通风流）的窗户时，您可能已经注意到，茂密的冷空气沿着脚冲向。即使您在房间的另一侧，也可以感觉到这种效果，当冷空气与上面的温暖空气混合在一起时，冷空气会稍微变暖，但是仍然足够凉爽且独特，因为它像洪水在地板上像洪水一样流动。这些是我们家中，工业和更广泛环境的非常广泛的流体流量的一部分，已知的磁性增香。通风流对于理解病原体和疾病的传播很重要，冷境基本相同，但规模为100-1000公里。在行业中，必须计划危险气体的意外泄漏，并进行适当的防御措施。重力电流的一个非常危险的子集是粒子驱动的电流，悬浮的颗粒载荷可提供驱动密度并促进巨大的破坏力。例如，粉末雪雪崩在山区是一种危险，很容易掩埋人们和建筑物。火山碎屑密度电流，火山释放的灰云云云，流过地面，著名地埋葬了庞贝，留下了一个被火山岩堆积在火山岩中的城市。大量的海底浊流，> 1000公里长，最多可移动10m/s，将养分和碳带入深海，并破坏了载有互联网数据或能源的许多电缆和管道。随着我们开发深海风力，必须通过电缆将其连接到岸上时，浊度较小（尽管仍然很大）会对英国构成越来越大的危险。这些和其他发展的可行性取决于我们预测和减轻自然危害的能力。正面电流将环境流体推开，而这里的动力学决定了电流的前进速率。此外，该区域是混合的主要来源，对于某些电流，它也是床严重侵蚀的区域。随着电流与周围的流体混合在一起，它变得更加稀释，并且电流变得更大，同时使驾驶密度降低。相反，随着床侵蚀床的侵蚀，驾驶密度会增加。因此，前部对电流的进展产生非常强大的控制，混合和侵蚀过程是其中的关键部分。但是，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，从而限制了它们在短距离上流动的适用性，因此混合不会对整体密度产生实质性影响。此外，电流的前部是最危险的部分：使床快速侵蚀的相同过程可以促进巨大的破坏力。在这项基本的科学研究中，我将开发新的数学模型，以捕获重力 - 流动性的动态，包括混合和腐蚀过程。首先，使用新开发的技术的实验性工作将产生前所未有的质量数据，以使温度驱动的电流，测量涡流的细节并在电流头和整个过程中混合。其他实验将集中于捕获沉积物驱动电流中侵蚀过程的细节。通过这些测量结果，我将首次在新的数学模型中捕获头部动力学的重要方面，包括混合和侵蚀过程。最后，我先前开发的电流模型将与我先前开发的电流的模型结合使用，以提供一个可以预测电流运动的完整模型。这个急需的项目代表了我们对这种重要和危险的流动类别的理解和预测能力的实质性跃升。