论文标题
运动学和磁性边界条件对对流驱动平面层发电机动力学的影响
Effects of kinematic and magnetic boundary conditions on the dynamics of convection-driven plane layer dynamos
论文作者
论文摘要
使用DNS在不同的运动学和磁边界条件下研究了快速旋转的对流驱动的发电机。以固定的旋转速率，以Ekman数字$ e = 5 \ times10^{ - 7} $表示，热力强迫在对流开始时的价值从2到20倍（$ \ MATHCAL {r} = ra/ra_c = 2-20 $），使流体属性（$ pr = pr = pr_m = 1 $）。发电机的统计行为，力平衡和热传输特性取决于决定边界层和内部动力学的边界条件。在固定的热强迫（$ \ Mathcal {r} = 3 $）下，在存在粘性边界层的情况下，Ekman羽毛会导致能量涡流，从而导致与自由滑动边界相比，带有无滑动边界的较高的腹膜和动力学螺旋。磁场的结构和强度也取决于边界条件。尽管领先的阶力平衡仍然是地球形式，但洛伦兹力以无滑动（无电导壁）的热边界层内部占主导地位。在这里，发现湍流动能预算中的洛伦兹工作术语具有将能量从速度场交换到磁场的组成部分，反之亦然。然而，在无滑动的隔离墙的情况下，所有洛伦兹的工作组件都执行单向能传递，以从流体的动能中产生磁能。与非磁性旋转对流相比，发热增强功能在$ \ MATHCAL {R} = 3-5 $的范围内显示出峰值。对于自由滑移条件，发电机的作用可能通过抑制大型涡流的形成来改变热传输。但是，当边界无滑动，电气传导壁时，就会发生最高的传热增强。
Rapidly rotating convection-driven dynamos are investigated under different kinematic and magnetic boundary conditions using DNS. At a fixed rotation rate, represented by the Ekman number $E=5\times10^{-7}$, the thermal forcing is varied from 2 to 20 times its value at the onset of convection ($\mathcal{R}=Ra/Ra_c=2-20$), keeping the fluid properties constant ($Pr=Pr_m=1$). The statistical behavior, force balance and heat transport characteristics of the dynamos depend on boundary conditions that dictate both boundary layer and the interior dynamics. At a fixed thermal forcing ($\mathcal{R}=3$), the Ekman plumes in the presence of viscous boundary layers lead to energetic vortices that result in higher enstrophy and kinetic helicity with no-slip boundaries compared to free-slip boundaries. The structure and strength of the magnetic field are also dictated by the boundary conditions. Though the leading order force balance remains geostrophic, Lorentz force dominates inside the thermal boundary layer with no-slip, electrically conducting walls. Here, the Lorentz work term in the turbulent kinetic energy budget is found to have components that exchange energy from the velocity field to the magnetic field, and vice-versa. However, with no-slip, insulated walls, all Lorentz work components perform unidirectional energy transfer to produce magnetic energy from the kinetic energy of the fluid. The heat transfer enhancement in dynamos, compared to non-magnetic rotating convection, exhibits a peak in the range $\mathcal{R}=3-5$. For free-slip conditions, dynamo action may alter the heat transport by suppressing the formation of large-scale vortices. However, the highest heat transfer enhancement occurs when the boundaries are no-slip, electrically conducting walls.
