[D*]stratify: harnessing energetics to control thermally stratified fluids

大家都知道，暖空气上升，冷空气下沉。然而，这一看似简单的现象的含义既没有得到广泛的理解，也没有得到适当的理解。这种现象产生了温度的垂直变化，即所谓的热分层，在土木工程和环境工程中发挥着深远的作用。热分层决定了在房间最低处产生舒适温度所需的热能和机械能。通过限制空气流动的方向，热分层还决定了空气传播病原体的最终命运，因此对影响SARS-CoV-2等病毒在建筑物内的传播至关重要。在油藏管理中，热分层在生物学上通常是不可取的；因此，能量被用于混合以使水分层。另一方面，在水箱中，热分层被用作存储太阳能的一种有效手段。在所有情况下，评估适当的设计和控制策略都需要了解热流体和冷流体如何相互作用来产生或破坏层结，这是当前湍流研究前沿的一个极具挑战性的开放问题。本项目将解决由于受限空间的非均匀加热和冷却而产生的热分层预测的突出问题，并最终形成一种称为[D*]分层的设计工具，该工具将通过识别和使用有限数量的关键测量来实现分层的预测和控制。我们的方法将超越现有的模型，通过发现和解释湍流羽流和热层化背后的能量，将理论与实时测量相结合。利用现有的基础设施，我们将启动一个独特的工作实验室来产生热分层，同时还将直接对受限湍流羽流进行数值模拟。我们的发现和建模将促进热分层的预测、设计和操作，以供研究和操作，同时提供有关潜在能量转换的基本信息。

Everyone knows that warm air rises and cold air sinks. Yet the implications of this apparently simple phenomenon are neither widely appreciated nor properly understood. The phenomenon produces vertical variations in temperature, known as thermal stratifications, that play a profound role in civil and environmental engineering. Thermal stratifications determine how much thermal and mechanical energy is needed to produce comfortable temperatures in the lowest parts of a room. By restricting the direction of air flow, thermal stratifications also determine the eventual fate of airborne pathogens and are therefore crucial in influencing the spread of viruses such as SARS-CoV-2 inside buildings. In reservoir management, thermal stratification is often biologically undesirable; hence energy is used for mixing to destratify the water. In water tanks, on the other hand, thermal stratifications are used as an effective means of storing solar-thermal energy. In all cases, the evaluation of appropriate design and control strategies requires understanding of how hot fluid and cold fluid interact to produce or destroy a stratification, which is an extremely challenging and open question at the forefront of current research in turbulence.This project will address the outstanding problem of predicting the thermal stratifications that are produced by non-uniform heating and cooling of a confined space and culminate in a design tool called [D*]stratify, which will enable the prediction and control of stratifications by identifying and using a limited number of key measurements. Our approach will transcend existing models by discovering and accounting for the energy behind turbulent plumes and thermal stratifications, coupling theory with real-time measurements. Utilising existing infrastructure, we will initiate a unique working laboratory for producing thermal stratifications, alongside direct numerical simulations of confined turbulent plumes. Our discoveries and modelling will facilitate the prediction, design and manipulation of thermal stratifications for both research and operation, whilst providing fundamental information about the underlying energy conversions.