Supporting data for "Experimental Studies of Turbulent Thermal Convection with Rotation and Latitudinal Libration"

Turbulent convective flows in geophysics and astrophysics are greatly affected by the celestial body's rotation. For instance, the famous Hadley cell in the atmosphere of Earth is considered a global tropical circulation caused by the combination of convection and rotation. In addition, the rotational dynamics of planetary bodies are not always constant but perturbed by gravitational interactions with their orbital partners. Motivated by these, turbulent thermal convection with rotation and latitudinal libration (one kind of perturbation) are experimentally studied in this thesis.First, the properties of heat transport and flow structures in rotating thermal convection are experimentally investigated. The heat transport efficiency exhibits a scaling transition at a transitional Ekman number Ekc, at which sharp transitions of the dynamical and geometrical properties of the columnar structures also occur. This excellent correspondence reveals that the behaviours of heat transfer efficiency are intimately related to the changes in coherent structures in the bulk flow, which in turn does not support the alternative boundary layer-competition mechanism. The sharp transition at Ekc also provides the first crystal-clear experimental evidence for the regime transition from convective Taylor column regime to plume regime, at which the columns break down due to the increased inertial effect. These results offer insights into the planetary dynamo studies, especially for the dipole reversals of the geodynamo near the dipole-multipole transition.Second, the weak centrifugal effects in rotating thermal convection are investigated experimentally. The analysis of the flow field reveals that in contrast to instantaneous quantities, the influence of the weak centrifugal force on long-time averaged quantities cannot be ignored. Therefore, the onset issue of centrifugal effects is studied systematically by the long-time averaged bulk temperatures, and the onset Froude number Frc is found to scale with the Rayleigh number (Ra) as Frc~Ra0.55. This 0.55 scaling can be reasonably well explained by the measured results of inter-column distance l0, which is related to Frc through a local force balance argument. In addition, the standard deviations of the bulk temperatures are analyzed to show well power-law scalings with both Ra and Ek.Finally, we report an experimental study on the effects of latitudinal libration on rotating thermal convection. Forced inertial modes obtained from the proper orthogonal decomposition (POD) take the form of an azimuthally travelling wave, which traps hot and cold fluid near thermal boundary layers, thus inhibiting the global heat transport properties. In particular, this heat transport inhibition is strongly enhanced when the forced inertial modes are amplified by the direct resonance. However, the heat transfer inhibition also becomes smaller when this amplification is weakened with intensified convection. These results may provide some implications for why Mercury has a large amount of water ice buried at its north and south poles.

在地球物理学和天体物理学领域，湍流对流流动受到天体自转的显著影响。例如，地球上大气的著名哈德莱环流被认为是由于对流与自转的结合而形成的全球性热带环流。此外，行星体的旋转动力学并非始终恒定，而是受到与其轨道伙伴之间的引力相互作用的扰动。受此启发，本论文对带有旋转和纬度摆动的湍流热对流（一种扰动形式）进行了实验研究。首先，对旋转热对流中热传输特性和流动结构的性质进行了实验探究。热传输效率在过渡的厄曼数 (E_{ ext{kc}}) 处表现出尺度转换，此时柱状结构的动力学和几何性质也发生急剧变化。这种卓越的对应关系揭示了热传输效率的行为与整体流动中的一致结构的变化密切相关，这反过来又否定了替代的边界层竞争机制。在 (E_{ ext{kc}}) 处的急剧转换还首次提供了从对流泰勒柱状流态到羽流态的态转变的清晰实验证据，此时柱状结构因惯性效应的增强而崩溃。这些结果为行星动力学研究提供了洞见，特别是对于地磁近极-多极过渡处的偶极反转。其次，对旋转热对流中的弱离心力效应进行了实验研究。对流动场的分析表明，与瞬时量相比，弱离心力对长时间平均量的影响不容忽视。因此，通过长时间平均的整体温度系统地研究了离心力效应的起始问题，并发现起始弗劳德数 (F_{ ext{rc}}) 与雷利数 (R_a) 成比例，即 (F_{ ext{rc}} sim R_a^{0.55})。这种 0.55 的比例关系可以通过测量到的柱间距离 (l_0) 的结果得到合理解释，该距离与 (F_{ ext{rc}}) 通过局部力平衡论联系起来。此外，通过分析整体温度的标准差，展示了与 (R_a) 和 (E_{ ext{kc}}) 均呈幂律关系的良好特征。最后，我们报告了对纬度摆动对旋转热对流影响的实验研究。通过适当的正交分解（POD）获得的强制惯性模式呈径向传播波的形式，这会在热边界层附近捕获热冷流体，从而抑制全局热传输特性。特别是，当强制惯性模式通过直接共振得到增强时，这种热传输抑制会显著增强。然而，当这种增强随着对流强度的增加而减弱时，热传输抑制也会减小。这些结果可能对解释水星南北极附近大量水冰的埋藏提供一些启示。