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arXiv 1406.4072physics.flu-dyn
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在逆级联的边缘

On the edge of an inverse cascade

Kannabiran Seshasayanan, Santiago Jose Benavides, Alexandros Alexakis

摘要:

我们证明了具有参数控制逆级联的系统可以表现出临界行为,在控制参数的临界值处,逆级联停止。在这样一个临界点附近,标准的能量平衡的唯象估计将失败,因为大尺度的能量通量变为零。我们证明了这些概念,使用计算易处理的二维磁流体力学模型在一个周期性的盒子。在没有任何外部磁强迫的情况下,系统减少到具有逆能量级联的流体动力学流体湍流。在强磁场作用下,系统表现为具有前向能量级联的二维磁流体动力学湍流。当磁强迫的幅度变化时,达到一个临界值,在该临界值下,朝向大尺度的能通量变为零。接近这一点的能量通量的规模作为一个幂律与偏离临界点和归一化振幅的波动发散。类似的行为被观察到的平方矢量位的磁通量,其中没有观察到的弱磁强迫的逆通量,而有限的逆通量观察到的临界点以上的磁强迫。我们推测,这种行为是通用的变量逆级联系统。

英文摘要:

We demonstrate that systems with a parameter-controlled inverse cascade can exhibit critical behavior for which at the critical value of the control parameter the inverse cascade stops. In the vicinity of such a critical point standard phenomenological estimates for the energy balance will fail since the energy flux towards large length scales becomes zero. We demonstrate these concepts using the computationally tractable model of two-dimensional magneto-hydrodynamics in a periodic box. In the absence of any external magnetic forcing the system reduces to hydrodynamic fluid turbulence with an inverse energy cascade. In the presence of strong magnetic forcing the system behaves as 2D magneto-hydrodynamic turbulence with forward energy cascade. As the amplitude of the magnetic forcing is varied a critical value is met for which the energy flux towards the large scales becomes zero. Close to this point the energy flux scales as a power law with the departure from the critical point and the normalized amplitude of the fluctuations diverges. Similar behavior is observed for the flux of the square vector potential for which no inverse flux is observed for weak magnetic forcing, while a finite inverse flux is observed for magnetic forcing above the critical point. We conjecture that this behavior is generic for systems of variable inverse cascade.

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