论文标题
二维雷利 - 纳德对流中的区域流动逆转
Zonal flow reversals in two-dimensional Rayleigh-Bénard convection
论文作者
论文摘要
我们分析了雷利 - 纳德对流中大规模流动的非线性动力学，其纵横比$γ$的二维矩形几何形状。我们分别在流向和跨度方向上施加周期性和自由滑道边界条件。随着瑞利数量RA的增加，大型层流流占据了中等prandtl数字流体的动力学。在湍流方案中，在高RA中，在最大规模模式的概率密度函数（PDF）中看到了过渡。对于$γ= 2 $，PDF首先从高斯向三峰行为过渡，这表示区域流动的逆转的出现，其中流动在三个不同的湍流状态之间波动：两个状态在两个状态下，其中相反方向和一个状态没有区域平均流量。 RA的进一步增加导致从三座向单峰PDF的过渡，这表明了区域流动逆转的消失。另一方面，对于$γ= 1 $，区域流动逆转的特征是最大尺度模式的双峰PDF，其中该流量仅在两个不同的湍流状态之间波动，沿相反方向传播的区域流动。
We analyse the nonlinear dynamics of the large scale flow in Rayleigh-Bénard convection in a two-dimensional, rectangular geometry of aspect ratio $Γ$. We impose periodic and free-slip boundary conditions in the streamwise and spanwise directions, respectively. As Rayleigh number Ra increases, a large scale zonal flow dominates the dynamics of a moderate Prandtl number fluid. At high Ra, in the turbulent regime, transitions are seen in the probability density function (PDF) of the largest scale mode. For $Γ= 2$, the PDF first transitions from a Gaussian to a trimodal behaviour, signifying the emergence of reversals of the zonal flow where the flow fluctuates between three distinct turbulent states: two states in which the zonal flow travels in opposite directions and one state with no zonal mean flow. Further increase in Ra leads to a transition from a trimodal to a unimodal PDF which demonstrates the disappearance of the zonal flow reversals. On the other hand, for $Γ= 1$ the zonal flow reversals are characterised by a bimodal PDF of the largest scale mode, where the flow fluctuates only between two distinct turbulent states with zonal flow travelling in opposite directions.
