权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

How does stably-stratified shear-driven turbulence mix our oceans and estuaries?

稳定分层的剪切驱动湍流如何混合我们的海洋和河口？

基本信息

批准号：
NE/W008971/1
负责人：
Adrien Lefauve
金额：
$ 89.48万
依托单位：
University of Cambridge
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=NE%2FW008971%2F1
关键词：
How does stably stratified shear

项目摘要

This research is ultimately motivated by reducing the harmful consequences of climate change on society, in the UK and worldwide.The root of the problem is global warming, caused by the greenhouse effect of carbon dioxide from fossil fuels. As our atmosphere warms, so do our oceans, which directly affects biodiversity and causes sea levels to rise. As our oceans warm, the balance of forces that keep them in constant motion changes too, disrupting their worldwide circulation. This disruption is worrying, both in the short and long term, because the present circulation patterns perform at least two functions vital to our hospitable climate. First, vertical currents store excess heat and carbon deep into the ocean (slowing global warming). Second, North-South currents redistribute tropical heat to more temperate regions (reducing extreme weather and climate). Therefore, a weakening of these currents could accelerate climate change, with long-lasting societal consequences.To mitigate this, scientists try to predict how the world's climate will evolve by using advanced mathematical and computer models of the ocean circulation. However, these models and their predictions need to be improved to be of greater benefit to society and decision-makers. A serious cause of uncertainty in these models lies in the mixing between water currents that have different salinity or temperature (and thus density). Currents of different densities organise into vertically-stacked (or "stably-stratified") layers which flow past one another at different speeds (creating a "shear" flow). These flows are always turbulent, which means that a vast number of tiny chaotic "eddies" mix the salinity and temperature of much larger layers in complex and unpredictable ways.This fundamental but extremely challenging process of turbulent mixing in stably-stratified shear flows needs to be better understood. To do this, I will employ the following scientific approach in three steps.First, I will use an accurate, reduced-scale model of such flows in the laboratory. This has two great benefits: it gives full control over the flow geometry, the density difference, flow speed, etc, allowing me to test and understand the influence of each parameter separately; and it allows me to use high-tech measurements to quantify the chaotic eddies and their mixing better than ever before.Second, I will interpret these new laboratory measurements with mathematical models of turbulent mixing to generalise (or "extrapolate") my findings to real-scale flows found in the ocean. This crucial step relies on the power of "dimensional analysis" in fluid dynamics, which is also routinely used by engineers to develop new aircraft or ship designs from smaller-scale laboratory prototypes.Third, I will verify the validity of my real-scale predictions by comparing them to actual measurements taken from ships (which are usually sparse, expensive, and less accurate). This step is similar to engineers performing a full-scale test before production, except that we have no control over the ocean. Although challenging, this "validation" step will help ensure that my whole approach succeeds in providing climate scientists with more accurate models for ocean mixing.In addition to the long-term effects of global warming, I will also apply the above three steps to a shorter-term consequence: saltwater intrusions in estuaries. Sea level rise, more frequent droughts, extreme storm surges, and stronger tides will all increase the gradual encroachment of seawater in densely-populated deltas (including the important Thames Basin in the UK). The upstream intrusion of a dense saltwater layer beneath the fresh river water, and their vertical mixing reduce the availability of surface freshwater, with devastating consequences for coastal communities already felt around the world. I will develop more accurate models of mixing in saltwater intrusions to help mitigate this urgent problem.

这项研究的最终目的是减少气候变化对英国和世界各地社会的有害影响。问题的根源是全球变暖，这是由化石燃料产生的二氧化碳的温室效应造成的。随着我们的大气层变暖，我们的海洋也在变暖，这直接影响到生物多样性，并导致海平面上升。随着我们的海洋变暖，使它们不断运动的力量平衡也发生了变化，扰乱了它们的全球循环。这种破坏在短期和长期都令人担忧，因为目前的环流模式至少对我们的宜人气候起着两种至关重要的作用。首先，垂直洋流将多余的热量和碳储存在海洋深处（减缓全球变暖）。其次，南北洋流将热带的热量重新分配到更温和的地区（减少极端天气和气候）。因此，这些洋流的减弱可能会加速气候变化，带来长期的社会后果。为了缓解这一问题，科学家们试图通过使用先进的海洋环流数学和计算机模型来预测世界气候将如何演变。然而，这些模型及其预测需要改进，以便为社会和决策者带来更大的利益。这些模型中不确定性的一个严重原因在于具有不同盐度或温度（以及密度）的水流之间的混合。不同密度的水流组织成垂直堆叠（或“稳定分层”）的层，这些层以不同的速度彼此流过（产生“剪切”流）。这些流动总是湍流的，这意味着大量微小的混乱“漩涡”以复杂和不可预测的方式混合了更大层的盐度和温度。需要更好地理解稳定分层剪切流中湍流混合的基本但极具挑战性的过程。为了做到这一点，我将分三步采用以下科学方法。首先，我将在实验室中使用此类流动的准确的缩小比例模型。这有两大好处：它可以完全控制流动的几何形状、密度差、流速等，使我能够分别测试和了解每个参数的影响;它使我能够使用高科技测量来量化混乱的漩涡和它们的混合比以往任何时候都好。第二，我将用湍流混合的数学模型来解释这些新的实验室测量结果，以进行概括（或“外推”）我的发现，以实际规模的流动发现在海洋中。这一关键步骤依赖于流体动力学中“量纲分析”的力量，工程师也经常使用它来从较小规模的实验室原型开发新的飞机或船舶设计。第三，我将通过将我的真实规模预测与从船舶上获得的实际测量结果（通常是稀疏的，昂贵的，准确性较差）进行比较来验证我的真实规模预测的有效性。这一步类似于工程师在生产前进行全面测试，只是我们无法控制海洋。尽管具有挑战性，但这个“验证”步骤将有助于确保我的整个方法成功地为气候科学家提供更准确的海洋混合模型。除了全球变暖的长期影响外，我还将将上述三个步骤应用于短期后果：河口的盐水入侵。海平面上升、更频繁的干旱、极端风暴潮和更强的潮汐都将增加海水对人口密集的三角洲（包括英国重要的泰晤士河流域）的逐渐侵蚀。淡水之下的密集盐水层的上游侵入及其垂直混合减少了地表淡水的可用性，对世界各地的沿海社区造成了破坏性后果。我将开发更精确的盐水入侵混合模型，以帮助缓解这一紧迫问题。