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Low Reynolds number laboratory and numerical simulations of high Reynolds number turbulent mixing

低雷诺数实验室和高雷诺数湍流混合的数值模拟

基本信息

批准号：
EP/E00847X/1
负责人：
John Vassilicos
金额：
$ 46.46万
依托单位：
Imperial College London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2006
资助国家：
英国
起止时间：
2006 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FE00847X%2F1
关键词：
Low Reynolds number laboratory numerical

项目摘要

Turbulence may appear random but we now know that there is much orderand coherent/persistent flow structure embedded in its randomness. Turbulence also consists of eddies of many different sizes with a mix of random and coherent/persistent behaviour at each scale. As a result of this multi-scale structure with its mix of disorder and persistent order, turbulent flows are good mixers. However, they consume a lot of energy to be maintained. Laminar flows require less energy consumotion. The purpose of this research is twofold. Firstly, to create and control new classes of flows which are laminar yet with multi-scale flow structure of eddies within eddies. The potential advantages for the design of new effiicient mixers is enormous. Secondly, to understand how the multi-scale eddying structure and its coherent and random components impact on stirring and mixing. Such an understanding has never been attempted as it is very difficult to ground it on laboratory experiments of turbulent flows where monitoring,let alone controlling, the turbulent eddy structure whilst, at the same time, measuring statistics and properties of the resulting stirring and mixing is virtuallly impossible. Instead, we propose to create fully controllled multi-scale bespoke turbulent-like flows with controlled multi-scale topologies (characterised in terms of hyperbolic and elliptic stagnation points and fractal dimensions) and controlled time-dependencies of the flows. With such multi-scale control in space and time of such bespoke flows, it is then possible to study the relations between the various elements of the turbulent-like flow structure (multi-scale streamline topology, time dependence, imposed randomness and persistence, etc) and the various statistics and properties of the flows (e.g. how much energy at each scale, i.e energy spectra) and of their stirring and mixing proporties (e.g. mixing rates, rate of separation of neighboring fluid elements, etc). At a subsequent stage, such detailed spatio-temporal topological understanding of these fully controlled bespoke laboratory flows will procvide the conceptual tools and framework and the type of knowledge necessary to derive models of turbulent mixing based on the actual persistent topology of the turbulence and its time dependence. Turbulent mixing models to this date effectively assume the turbulence to be no more than just a random mixer, and such models are known to be fundamentally flawed.

湍流可能看起来是随机的，但我们现在知道，在其随机性中嵌入了许多有序和连贯/持续的流动结构。湍流还由许多不同大小的涡旋组成，在每个尺度上混合了随机和连贯/持续的行为。由于这种多尺度结构，以及无序和持续有序的混合，湍流是很好的混合器。然而，它们需要消耗大量的能源才能进行维护。层流需要较少的能量消耗。这项研究的目的有两个。首先，创建和控制具有多尺度涡内涡流结构的层流新流类。设计新型高效混合器的潜在优势是巨大的。其次，了解多尺度涡旋结构及其相干和随机成分对搅拌和混合的影响。这样的理解从未被尝试过，因为很难将其建立在湍流的实验室实验上，在这些实验中，监测湍流涡旋结构，同时测量所产生的搅拌和混合的统计数据和性质实际上是不可能的，更不用说控制了。相反，我们建议创建完全受控的多尺度定制湍流类流动，具有受控的多尺度拓扑(根据双曲和椭圆停滞点和分形维的特征)和受控的时间依赖性流动。利用这种定制流动在空间和时间上的多尺度控制，可以研究类湍流流动结构的各种元素(多尺度流线拓扑、时间依赖性、强加的随机性和持久性等)与流动的各种统计和性质(例如，每个尺度上有多少能量，即能量谱)以及它们的搅拌和混合特性(例如，混合速率、相邻流体元素的分离速率等)之间的关系。在接下来的阶段，对这些完全可控的定制实验室流动的这种详细的时空拓扑理解将提供根据湍流的实际持续拓扑及其时间相关性推导湍流混合模型所需的概念工具和框架以及所需的知识类型。到目前为止，湍流混合模型实际上假设湍流只是一个随机混合器，而且这种模型从根本上是有缺陷的。