磁旋转Turbulence中的带状流动和长寿命轴对称压力凸点
Zonal Flows and Long-Lived Axisymmetric Pressure Bumps in Magnetorotational Turbulence
摘要：
我们研究了剪切盒模拟中磁旋转湍流的行为，径向和方位角范围高达十个尺度高度。麦克斯韦和雷诺应力被发现增加超过一个因素时，两个尺度的高度在径向方向上的盒的大小增加。进一步增加盒子的尺寸对湍流的统计特性影响很小或没有影响。逆级联在盒子的最大尺度上激发磁场结构。麦克斯韦应力相应的10%变化会引发亚克普勒速度和超克普勒速度交替的带状流。这反过来又在压力和科里奥利力之间的地转平衡中产生带状密度结构。我们提出了一个简化的模型的外观纬向流，在短时间尺度上的磁张力随机强迫创建纬向流结构的寿命的几十个轨道。我们实验了各种改进的剪切盒算法，以减少由超声速剪切流引入的数值扩散。虽然一个标准的有限差分平流方案显示出抑制的迹象附近的边缘的盒子的湍流活动，这个问题是消除了一个新的方法，其中开普勒剪切平流提前在傅立叶空间插值的时间。
英文摘要：
We study the behavior of magnetorotational turbulence in shearing box simulations with a radial and azimuthal extent up to ten scale heights. Maxwell and Reynolds stresses are found to increase by more than a factor two when increasing the box size beyond two scale heights in the radial direction. Further increase of the box size has little or no effect on the statistical properties of the turbulence. An inverse cascade excites magnetic field structures at the largest scales of the box. The corresponding 10% variation in the Maxwell stress launches a zonal flow of alternating sub- and super-Keplerian velocity. This in turn generates a banded density structure in geostrophic balance between pressure and Coriolis forces. We present a simplified model for the appearance of zonal flows, in which stochastic forcing by the magnetic tension on short time-scales creates zonal flow structures with life-times of several tens of orbits. We experiment with various improved shearing box algorithms to reduce the numerical diffusivity introduced by the supersonic shear flow. While a standard finite difference advection scheme shows signs of a suppression of turbulent activity near the edges of the box, this problem is eliminated by a new method where the Keplerian shear advection is advanced in time by interpolation in Fourier space.
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