Nonlinear Equilibration and Turbulent Cascades in Laboratory Studies of Baroclinic Turbulence

斜压湍流实验室研究中的非线性平衡和湍流级联

基本信息

批准号：
EP/K029428/1
负责人：
Peter Read
金额：
$ 47.45万
依托单位：
University of Oxford
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2014
资助国家：
英国
起止时间：
2014 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FK029428%2F1
关键词：
Nonlinear Equilibration Turbulent Cascades Laboratory

项目摘要

Complex interactions between turbulent convection and stably-stratified flows in the presence of background rotation are important for a wide range of problems in various engineering contexts, in atmospheric and oceanic science, and in stellar and planetary astrophysics. This project will investigate the nature of flows between a heat source and a heat sink that are displaced both vertically and horizontally relative to each other, in the presence of strong background rotation. In the absence of background rotation, if a heat source is located at a lower altitude than the sink, one would generally expect a strongly convective circulation to result, carrying heat directly and vigorously from the source to the sink. With background rotation, however, evidence from experiments, simulations and in geophysical flows suggest that the resulting circulation may spontaneously partition itself into a convectively unstable/neutral region (where temperature becomes well mixed and doesn't vary much with height) that interacts with a statically stable, so-called baroclinic region (where temperature increases with height and develops a thermal gradient from one side to the other). Wave-like instabilities may develop within this baroclinic zone that may play a crucial role in stabilising the vertical stratification and dominating the transfer of heat and momentum where they occur. Moreover, there is evidence to suggest that if the transport of heat by the instability acts more rapidly than other heat exchange processes, this stabilizing effect may act within a nonlinear feedback loop, somewhat like a thermostat, adjusting the flow back towards a weakly nonlinear/unstable 'critical' state - sometimes referred to as 'self-organized criticality'. Such strongly nonlinear and convective motions are difficult to model accurately, however, so the mechanisms involved, though probably ubiquitous in certain engineering systems and in nature, are not well understood.We therefore propose to set up an experimental configuration which entails heating a body of fluid in a cylindrical container on a rotating platform along an annular ring at the bottom of the tank close to the outer radius, and cooling it through a circular disk near the centre of the tank at the upper surface. Preliminary numerical simulations and experiments (carried out in my group and with proposed collaborators in the USA and Spain) already suggest that such flows will readily form a statically stable (though baroclinically unstable) zone between convectively unstable regions over/underlying the heated or cooled boundaries. We therefore plan to measure the characteristics of the resulting flows through combinations of in situ thermal sensors and particle image velocimetry (PIV) techniques, including the innovative possibility of using thermochromic liquid crystal particles to determine velocities and temperatures simultaneously within the flow. This will facilitate the determination of flow structures, heat and momentum transports within the flow, and to characterize the development of any kinetic energy cascades that may emerge as more turbulent regimes are explored. The idealised nature of these experiments should ensure that the results obtained will be applicable to a wide variety of problems in various disciplines.Such a configuration may be seen as an idealisation of a variety of industrial processes (e.g. in rotating semiconductor crystal growth melts, process mixing techniques in chemical engineering, convective flows in turbomachinery etc.), and of a number of geophysical and astrophysical problems in which stably and unstably stratified flows interact in the presence of background rotation. These include the Earth's atmosphere and climate system and its response to variations in its radiative heating and cooling, other planetary atmospheres (notably Mars, Venus and the gas giant planets), and in stellar interiors (e.g. the tachocline region within the Sun).

在背景旋转的情况下，湍流对流与稳定分层流之间的复杂相互作用对于在各种工程环境，大气和海洋科学以及恒星和行星天体物理学中的各种问题中都很重要。该项目将研究在存在强背景旋转的情况下，垂直和水平相对于彼此垂直和水平移动的散热器之间的流动性质。在没有背景旋转的情况下，如果热源位于水位低于水槽的高度，通常会期望会产生强烈的对流循环，从而直接从源到水槽直接迅速携带热量。 With background rotation, however, evidence from experiments, simulations and in geophysical flows suggest that the resulting circulation may spontaneously partition itself into a convectively unstable/neutral region (where temperature becomes well mixed and doesn't vary much with height) that interacts with a statically stable, so-called baroclinic region (where temperature increases with height and develops a thermal gradient from one side to the other).波浪状的不稳定性可能会在这个斜压区域内发展，该区域可能在稳定垂直分层和主导发生的热量和动量的转移中起着至关重要的作用。此外，有证据表明，如果不稳定性的热传输比其他热交换过程更快，则这种稳定效应可能在非线性反馈循环中起作用，有点像一个恒温器，将流量调节朝向弱的非线性/不稳定的“关键”状态，有时称为“自组织的临界质量”。但是，这种强烈的非线性和对流动作难以准确地建模，因此，涉及的机制，尽管可能在某些工程系统和自然界中无处不在，但在自然界中却没有充分理解。因此，我们建议我们建立一个实验构型，该配置需要在圆柱形的底部旋转的旋转平台上的圆形旋转平台中的旋转式旋转的旋转台上的圆形液体中的液体加热，并在底部的底部旋转，并在底部的底部旋转，并将其旋转，并在旋转的底部旋转，并在底部的旋转台上，沿底部的旋转状态，以使其在底部的旋转台上旋转，并将其旋转的旋转状态在底部的底部旋转。上表面的水箱。初步的数值模拟和实验（在我的小组中以及在美国和西班牙提议的合作者中进行的）已经表明，这种流程很容易在对流不稳定的区域之间静态稳定（尽管是横线上不稳定的）区域，而不稳定的区域则在加热或冷却的界限上/潜在的区域。因此，我们计划通过原位热传感器和粒子图像速度计（PIV）技术的组合来测量所得流的特性，包括使用热色液液体晶体颗粒来确定流量内同时确定速度和温度的创新可能性。这将有助于确定流量内的流量结构，热量和动量传输，并表征随着探索更湍流的方式，可能出现的任何动能能量级联反应的发展。这些实验的理想化性质应确保所获得的结果适用于各种学科中的各种问题。类似的配置可能被视为对各种工业过程的理想化（例如，半导体晶体生长融化中的旋转半导体晶体生长融化中，在化学工程中的过程混合技术，以及在化学工程中的过程混合，以及在化学工程中，以及在涡轮上的ersoph ersific and geoper等。在背景旋转的情况下，不稳定的分层流相互作用。这些包括地球的大气和气候系统及其对辐射加热和冷却的变化的反应，其他行星大气（尤其是火星，金星和气体巨型行星），以及在恒星的内部（例如，太阳中的速度线区域）。