The Magnetohydrodynamics of Liquid Metal Tornadoes (MAGNADO)

行星金属内部流体运动产生的大尺度磁场自激是流体动力学中最具挑战性的问题之一。这种所谓的发电机过程是由湍流旋转对流提供动力的，并涉及流动和感应电流之间的复杂反馈循环。由于行星发电机无法直接观测，数值模拟无法达到行星内部深处的极端条件，因此我们需要强有力的理论物理驱动的方法来阐明潜在的流动机制，并做出有意义和准确的预测。本研究的目的是研究旋转磁对流与离心浮力的新内容。离心浮力促进了大规模龙卷风状漩涡的形成。我假设，这些龙卷风是有利于发电机行动：其固有的性质是螺旋形的，打破镜像对称，因此，类似于经典的理论Ponomarenko发电机模型。此外，可以产生远高于自由落体极限的流速。液态金属中的直接数值模拟（DNS）将是寻找龙卷风形成和发电机作用的最佳点的核心。但将参数推到极端并不是这一努力的解决办法。相反，这些高度湍流的热惯性磁流体动力学流动的相互关联的非线性动力学的理解是必需的。为了达到这个目的，我们将依次考虑感应方程的更复杂的形式。相应的DNS和实验在液体镓和硫酸将提供一个详细的图片本地行星感应和发电机过程。该项目将最终在一个准确的前向模型的类似对流驱动的流体发电机设备，也是可实现的实验室规模，这是以前认为是不可能的。

The self-excitation of large-scale magnetic fields through fluid motion in the metallic interiors of planets is one of the most challenging problems in fluid dynamics. This so-called dynamo process is powered by turbulent rotating convection and involves a complex feedback cycle between the flow and the induced electrical currents. Because planetary dynamos are inaccessible to direct observation and numerical simulations cannot reach the extreme conditions prevailing deep inside planets, we need strongly theoretical-physics driven approaches to elucidate the underlying flow mechanisms and make meaningful and accurate predictions. The aim of the research proposed here is to study rotating magnetoconvection with the novel inclusion of centrifugal buoyancy. Centrifugal buoyancy promotes the formation of large-scale tornado-like vortices. I hypothesise that these tornadoes are favourable for dynamo action: Their inherent nature is helical, breaks mirror-symmetry, thus, resembling the classical theoretical Ponomarenko dynamo model. Additionally, flow speeds well above the free-fall limit can be generated. Direct numerical simulations (DNS) in liquid metals will be central for finding the sweet spot for tornado formation and dynamo action. But pushing the parameters to an extreme is not the solution for this endeavour. Instead, an understanding of the interconnected nonlinear dynamics of these highly turbulent thermal-inertial magnetohydrodynamic flows is required. To this end, successively more complex forms of the induction equation will be considered. Corresponding DNS and experiments in liquid gallium and sulfuric acid will provide a detailed picture of the local planetary induction and dynamo processes. The project shall culminate in an accurate forward model of an analogous convection-driven fluid dynamo device that is also realisable on a laboratory scale, which was previously thought impossible.