论文标题
连贯的解决方案和二维雷利 - 巴纳德对流的湍流过渡
Coherent Solutions and Transition to Turbulence in Two-Dimensional Rayleigh-Bénard Convection
论文作者
论文摘要
对于二维Rayleigh-Bénard对流,以前使用数值延续计算出不稳定的稳定解决方案(Waleffe,2015; Sondak,2015)。 “主要”稳定解决方案从传导状态下分叉为$ ra \ of约1708 $,并且特征性纵横比(长度/高度)约为$ 2 $。主要解决方案对应于一对逆时针旋转对流辊,侧面温度上升和侧面的下降气流。通过调整域的水平长度,(Waleffe,2015; Sondak,2015年)也发现了稳定的最大热传输解决方案,其特征纵横比小于$ 2 $,并且随着$ ra $的增加而减少。与主要溶液相比,最佳的热传输溶液对边界层厚度,羽流的水平长度尺度和下降气流的结构进行了修改。当前的研究建立了这些(不稳定)稳定的解决方案与湍流的过渡之间的直接联系,以$ pr = 7 $和$ pr = 100 $。对于$ ra $的过渡值,主要和最佳的热传输溶液在适当大小的时间不断变化的温度场中显着。对于$ ra $以外的过渡性,我们的数据分析显示了$ pr = 7 $的主要解决方案的持久性,而最佳的热传输解决方案则更容易检测到$ pr = 100 $。在这两种情况下,$ pr = 7 $和$ pr = 100 $,主要和最佳解决方案的相对流行率与数值数据和稳定解决方案的$ nu $ vs. $ ra $ scalings一致。
For two-dimensional Rayleigh-Bénard convection, classes of unstable, steady solutions were previously computed using numerical continuation (Waleffe, 2015; Sondak, 2015). The `primary' steady solution bifurcates from the conduction state at $Ra \approx 1708$, and has a characteristic aspect ratio (length/height) of approximately $2$. The primary solution corresponds to one pair of counterclockwise-clockwise convection rolls with a temperature updraft in between and an adjacent downdraft on the sides. By adjusting the horizontal length of the domain, (Waleffe, 2015; Sondak, 2015) also found steady, maximal heat transport solutions, with characteristic aspect ratio less than $2$ and decreasing with increasing $Ra$. Compared to the primary solutions, optimal heat transport solutions have modifications to boundary layer thickness, the horizontal length scale of the plume, and the structure of the downdrafts. The current study establishes a direct link between these (unstable) steady solutions and transition to turbulence for $Pr = 7$ and $Pr = 100$. For transitional values of $Ra$, the primary and optimal heat transport solutions both appear prominently in appropriately-sized sub-fields of the time-evolving temperature fields. For $Ra$ beyond transitional, our data analysis shows persistence of the primary solution for $Pr = 7$, while the optimal heat transport solutions are more easily detectable for $Pr = 100$. In both cases $Pr = 7$ and $Pr = 100$, the relative prevalence of primary and optimal solutions is consistent with the $Nu$ vs. $Ra$ scalings for the numerical data and the steady solutions.