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种普遍存在的过程，它发生在自然界和各种技术的许多情况下，从大气和行星（包括地球）和恒星的流体内部到工业过程，如化学工程，食品制备和发电。当对流发生在旋转系统中时，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，并显著影响热，动量甚至质量在流动中传输的效率。由于流动的复杂性和非线性反馈的作用，预测旋转的强度和不同的加热和冷却如何决定流动及其输运性质，并取决于其他因素，如系统的形状，这是特别困难的。众所周知，预测旋转热对流的性质对于确定大气、海洋和地球深部流动的形状和强度非常重要，例如，影响其气候和可预测性。但它对于诸如用于航空器推进和发电的燃气涡轮机发动机等装置的设计也是非常重要的。这些发动机的各种快速旋转部件内部的表面之间可能会产生强烈的温度对比，已经发现这会导致复杂的对流模式，从而显著影响这些部件内的热传递。随着这种发动机的设计者试图提高其燃料效率和性能，例如在涡轮机叶片和它们的叶片之间的制造公差变得越来越苛刻，需要在所有操作条件下严格控制整个发动机的温度。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对变化的条件作出反应的理解、建模和预测的能力是至关重要的。该项目旨在提高我们对旋转对流的理解，其条件类似于（a）涡轮机发动机部件内的旋转空腔内和（B）在大气和快速旋转行星内部遇到的高度湍流中发现的条件。我们计划构建一个实验室实验，通过加热或冷却内外圆柱壁，可以在快速旋转的圆柱环形槽（即两个同向旋转的同轴圆柱之间的空腔）内产生湍流对流。圆柱形腔体可以围绕竖直轴线以不同速度旋转，以包括由在竖直方向上作用的重力或由在径向方向上作用的离心力支配的条件。后者与地球或其他行星的涡轮机发动机或对流流体核心内的条件最相关，而前者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度范围内进行仔细控制的实验，我们的目标是确定如何从一个政权到另一个政权的流动特性的变化，并量化这些变化的影响，如热传递和大规模的相干结构，如涡流和带状射流的形成。这将是第一次在同一实验系统中研究这两种机制，使我们能够从工程科学和物理学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机发动机腔体的系统中的气流进行的数值模型模拟进行比较，以帮助提高他们预测气流结构和行为的能力。

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.