Breakdown of the large-scale circulation in Γ=1/2 rotating Rayleigh-Bénard flow.
Breakdown of the large-scale circulation in Γ=1/2 rotating Rayleigh-Bénard flow.
复制标题
DOI：
10.1103/physreve.86.056311
复制
发表时间：
2011-12
期刊：
影响因子：
--
通讯作者：
R. Stevens;H. Clercx;D. Lohse
中科院分区：
文献类型：
--
作者：
R. Stevens;H. Clercx;D. Lohse
圆柱形样品中旋转瑞利-贝纳德对流的实验和模拟表明，随着旋转速率的增加，热传输也会增加。这种热传输的增强与湍流结构从以大尺度环流（LSC）为主的状态（由单个对流辊组成，无旋转或弱旋转）到以强旋转时垂直排列的涡流为主的状态的转变密切相关。对于长径比为 Г=D/L=1（D 是样品直径，L 是其高度）的样品，两种状态之间的转变由 LSC 强度的强烈下降来指示。相反，对于 Γ=1/2，Weiss 和 Ahlers [J.流体机械。 688, 461 (2011)]揭示了超过临界旋转速率时类似LSC的侧壁温度特征的存在。他们认为，这可能是由于双涡流状态的形成，其中一个涡流从底部垂直延伸到样品内部并带来温暖的流体，而另一个涡流从顶部带来冷流体；该流场会产生类似于 LSC 的侧壁温度特征。在这里，我们通过直接数值模拟 Г=1/2 和允许与实验直接比较的参数表明，对流单元中垂直排列的涡流结构的空间组织确实产生（对于时间平均值）侧壁附近温度的正弦变化，如实验中发现的。这也是与 Γ=1 样本的本质且重要的区别，其中垂直排列的涡流是随机分布的。
Experiments and simulations of rotating Rayleigh-Bénard convection in cylindrical samples have revealed an increase in heat transport with increasing rotation rate. This heat transport enhancement is intimately related to a transition in the turbulent flow structure from a regime dominated by a large-scale circulation (LSC), consisting of a single convection roll, at no or weak rotation to a regime dominated by vertically aligned vortices at strong rotation. For a sample with an aspect ratio Γ=D/L=1 (D is the sample diameter and L is its height) the transition between the two regimes is indicated by a strong decrease in the LSC strength. In contrast, for Γ=1/2, Weiss and Ahlers [J. Fluid Mech. 688, 461 (2011)] revealed the presence of a LSC-like sidewall temperature signature beyond the critical rotation rate. They suggested that this might be due to the formation of a two-vortex state, in which one vortex extends vertically from the bottom into the sample interior and brings up warm fluid while another vortex brings down cold fluid from the top; this flow field would yield a sidewall temperature signature similar to that of the LSC. Here we show by direct numerical simulations for Γ=1/2 and parameters that allow direct comparison with experiment that the spatial organization of the vertically aligned vortical structures in the convection cell do indeed yield (for the time average) a sinusoidal variation of the temperature near the sidewall, as found in the experiment. This is also the essential and nontrivial difference with the Γ=1 sample, where the vertically aligned vortices are distributed randomly.