Non-Oberbeck-Boussinesq effects in turbulent convection in cryogenic helium at high Rayleigh numbers

高瑞利数低温氦中湍流对流的非奥伯贝克-布辛斯克效应

• 批准号: 450293408
• 负责人: Professor Dr. Jörg Schumacher
• 金额: --
• 依托单位: Institute of Scientific Instruments (ISI)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/450293408?language=en
• 关键词: Non; Oberbeck; Boussinesq; effects; turbulent

Experiments of turbulent Rayleigh-Bénard convection (RBC) in cryogenic helium gas reach the highest possible Rayleigh numbers with a vigorous turbulence under controlled laboratory conditions that come close to those in real atmospheric flows and can thus provide us deeper insights into the turbulent transport mechanisms of heat and momentum in these natural systems. These high Rayleigh numbers require however to operate the helium working fluid close to the phase boundary or even the critical point of the pressure-temperature phase plane which causes fluctuations of all material parameters such as kinematic viscosity or thermal conductivity. These fluctuations result in deviations from the Oberbeck-Boussinesq (OB) regime of thermal convection with a well-defined up-down symmetry of the flow and its statistics. In this project, we want to investigate these deviations -- the so-called non-Oberbeck-Boussinesq (NOB) effects -- and its impact on the turbulent transport systematically. Therefore we bring the expertise in cryogenic experiments on the Czech side and in massive direct numerical simulations of turbulent convection on the German side in a joint Czech-German proposal together. The detailed parameter dependencies on temperature and pressure will be obtained from the XHEPAK software that models the equation of state of the cryogenic helium gas in its full complexity. The resulting material parameter dependencies enter the numerical simulations and can be directly compared with the idealized OB limit as well as experiments at the same Rayleigh numbers. Our work helps to better understand the inconclusive results obtained in different high-Rayleigh-number laboratory experiments with respect to the existence of a transition of the RBC flow into the ultimate regime (with a significantly enhanced turbulent heat transfer).

在受控的实验室条件下，对低温氦气中的湍流瑞利-巴姆纳德对流（RBC）进行了实验，在剧烈的湍流中达到了可能的最高瑞利数，接近于真实的大气流动，从而可以为我们提供对这些自然系统中热量和动量的湍流传输机制的更深入的了解。然而，这些高瑞利数要求氦工作流体在接近相边界甚至压力-温度相平面的临界点处运行，这会导致所有材料参数（如运动粘度或导热系数）的波动。这些波动导致热对流的Oberbeck-Boussinesq （OB）模式的偏差，该模式具有良好的上下对称流动及其统计量。在这个项目中，我们想要系统地研究这些偏差——所谓的非奥贝克-布辛尼斯克（NOB）效应——及其对湍流传输的影响。因此，我们将捷克方面的低温实验专业知识和德国方面的大量直接湍流对流数值模拟专业知识结合在一起，形成了一项捷德联合提案。详细的参数对温度和压力的依赖关系将从XHEPAK软件中获得，该软件模拟了低温氦气的状态方程。由此产生的材料参数依赖关系进入数值模拟，可以直接与理想OB极限以及相同瑞利数下的实验进行比较。我们的工作有助于更好地理解在不同的高瑞利数实验室实验中获得的关于RBC流动过渡到最终状态（具有显著增强的湍流传热）的不确定结果。