We study the bifurcations of the large scale jets in the turbulent regime of a forced shear flow using direct numerical simulations of the Navier-Stokes equations. The bifurcations are seen in the probability density function (PDF) of the largest scale mode with the control parameter being the Reynolds number based on the friction coefficient denoted as $Rh$. As one increases $Rh$ in the turbulent regime, the PDF of the large scale mode first bifurcates from a Gaussian to a bimodal behaviour, signifying the emergence of reversals of the large scale flow where the flow fluctuates between two distinct turbulent states. Further increase in $Rh$ leads to a bifurcation from bimodal to unimodal PDF which denotes the disappearance of the reversals of the largest scale mode. We attribute the latter transition to the long-time memory that the large scale flow exhibits related to low frequency $1/f^{\alpha }$ type of noise with $0

中文翻译：

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二维剪切流中湍流状态之间的过渡

我们使用Navier-Stokes方程的直接数值模拟研究在强迫剪切流的湍流状态下的大型射流的分叉。在最大比例模式的概率密度函数（PDF）中可以看到分叉，其中控制参数为基于表示为摩擦系数的雷诺数$\mathrm{[R}H$。随着增加$\mathrm{[R}H$在湍流状态下，大型模式的PDF首先从高斯分岔为双峰行为，这表明出现了大流量逆转，其中流量在两个不同的湍流状态之间波动。进一步增加$\mathrm{[R}H$导致从双峰PDF到单峰PDF的分歧，这表明最大比例模式的反转消失了。我们将后者的转变归因于大流量与低频相关的长期记忆$\mathrm{1个}/F^{\alpha }$ $ 0的噪声类型