Characterising Flow Regimes and Transitions, Heat Transport and Energy/Enstrophy Cascades in Rapidly Rotating Thermal Convection

有什么问题吗？由热对流驱动的湍流是一个普遍存在的过程，它发生在自然界和各种技术的许多情况下，从行星（包括地球）和恒星的大气和流体内部到化学工程、食品制备和发电等工业过程。当对流在旋转系统中发生时，对流可能会从根本上改变其特性，形成与旋转轴对齐的相干结构，并显著影响流中热量、动量甚至质量传输的效率。由于流动的复杂性和非线性反馈的作用，预测旋转强度和不同的加热和冷却如何决定流动及其输运性质，以及依赖于系统形状等其他因素是特别困难的。为什么它很重要？众所周知，预测旋转热对流的特性对于确定大气、海洋和地球深处气流的形状和强度，例如影响其气候和可预测性，是非常重要的。但是，它对于诸如用于飞机推进和发电的燃气涡轮发动机等设备的设计也具有重要意义。这些发动机的各种快速旋转部件的表面之间可能会产生强烈的温度差异，这导致了复杂的对流模式，严重影响了这些部件内部的热量传递。由于此类发动机的设计者试图提高其燃油效率和性能，因此制造公差（例如涡轮叶片与其护罩之间的公差）变得越来越苛刻，要求在所有运行条件下对整个发动机的温度进行严密控制。因此，提高我们对这些发动机系统内部湍流对流的结构和行为以及它如何应对不断变化的条件的理解、建模和预测的能力至关重要。这个项目将实现什么目标？该项目旨在提高我们对以下条件下旋转对流的理解：(a)在涡轮发动机部件的旋转腔内，(b)在大气和快速旋转的行星内部遇到的高度湍流中。我们计划建立一个实验室实验，通过加热或冷却内、外圆柱体壁，在快速旋转的圆柱形环形罐（即两个共旋转的同轴圆柱体之间的腔体）内产生湍流对流。圆柱腔可以围绕垂直轴以不同速度旋转，以包括由作用于垂直方向的重力或作用于径向的离心力所支配的条件。后者与涡轮发动机内部或地球或其他行星的对流流体核心最相关，而前者则模拟行星大气或海洋中的条件。通过在广泛的旋转速率和热对比范围内进行仔细控制的实验，我们的目标是确定从一种状态到另一种状态的流动特征如何变化，并量化这些变化对传热等特性的影响，以及大规模连贯结构（如漩涡和纬向射流）的形成。这将是第一次在同一个实验系统中研究这两种机制，使我们能够从工程科学和地球物理领域获得对这些流动的新见解和理解。我们计划将我们的实验结果与巴斯大学、萨里大学和牛津大学的工程师对类似于燃气涡轮发动机腔的系统中气流的数值模型模拟进行比较，以帮助提高他们预测流动结构和行为的能力。

What is the problem?Turbulence driven by thermal convection is a ubiquitous process that occurs in many situations in both nature and in various technologies, ranging from the atmosphere and fluid interiors of planets (including the Earth) and stars through to industrial processes such as in chemical engineering, food preparation and power generation. When convection takes place in a rotating system, convection may radically change its character, developing coherent structures that align with the axis of rotation and significantly influence the efficiency by which heat, momentum and even mass are transported within the flow. Predicting how the strength of rotation and differential heating and cooling determine the flow and its transport properties and depend on other factors such as the shape of the system are especially difficult because of the complexity of the flow and the role of nonlinear feedbacks.Why is it important?Predicting the properties of rotating thermal convection is well known to be important in determining the shape and intensity of flows in the atmosphere, oceans and deep interior of the Earth, for example, influencing their climate and predictability. But it is also of major importance for the design of devices such as gas turbine engines used for aircraft propulsion and power generation. Strong temperature contrasts may develop between surfaces inside various rapidly rotating components of these engines that have been found to lead to complex convection patterns that significantly affect the transfer of heat within these components. As the designers of such engines attempt to improve their fuel efficiency and performance, manufacturing tolerances e.g. between turbine blades and their shrouds are becoming more and more demanding, requiring close control of temperatures throughout the engine under all operating conditions. It is vital, therefore, to improve our understanding of, and ability to model and predict, the structure and behaviour of the turbulent convection inside these engine systems and how it responds to changing conditions.What will this project achieve?This project seeks to improve our understanding of rotating convection under conditions that are similar to those found (a) inside rotating cavities within components of turbine engines and (b) in highly turbulent flows encountered in the atmospheres and interiors of rapidly rotating planets. We plan to construct a laboratory experiment that can generate turbulent convective flows inside a rapidly rotating cylindrical annular tank (i.e. the cavity between two co-rotating coaxial cylinders) by heating or cooling the inner and outer cylindrical walls. The cylindrical cavity can be rotated at different speeds about a vertical axis to include conditions that are either dominated by gravity acting in the vertical direction or by centrifugal forces acting in the radial direction. The latter are most relevant to conditions inside turbine engines or the convective fluid core of the Earth or other planets, while the former emulates the conditions found in planetary atmospheres or oceans. By conducting carefully controlled experiments over a broad range of rotation rate and thermal contrasts, we aim to determine how the flow changes in character from one regime to another and to quantify the impact of these changes on properties such as heat transfer and the formation of large-scale coherent structures such as vortices and zonal jets. This would be the first time both of these regimes would have been studied in the same experimental system, allowing us to gain new insights and understanding of these flows drawn from the fields of engineering science and geophysics. We plan to compare our experimental results with numerical model simulations obtained by engineers at the Universities of Bath, Surrey and Oxford of air flows in systems similar to gas turbine engine cavities to help improve their ability to predict flow structure and behaviour.