对流驱动剪切和热通量降低
Convectively driven shear and decreased heat flux
摘要：
我们报告直接数值模拟的二维，水平周期性的瑞利-贝纳德对流，专注于其能力，以驱动大规模的水平流动，垂直剪切。对于普朗特数（$Pr$）在1和10之间的模拟，这种大规模的剪切可以通过充分提高瑞利数（$Ra$）引起的，我们探讨了由此产生的对流$Ra$高达$10^{10}$。当出现在我们的模拟中时，剪切平均流占总动能的很大一部分，并且这一部分趋向于作为$Ra\to\infty$的1。剪切有助于分散对流结构，它减少了垂直热通量;在参数制度，其中一个国家与大规模的剪切和一个没有都是稳定的，努塞尔数的状态与剪切是较小的，增长更缓慢的$Ra$。当大尺度切变与$Pr\lesssim2$同时存在时，对流在长时间尺度上经历强烈的全球振荡，热输送以爆发形式发生。对于$Pr=1$，在这些突发上时间平均的努塞尔数随$Ra$非单调地变化。当剪切与$Pr\gtrsim3$一起存在时，流动不会破裂，并且对流热传输始终持续。努塞尔数随后大致以$Ra$的幂增长，但增长速率比以前报道的没有大尺度剪切的瑞利-贝纳德对流的增长速率要慢。我们发现当$Pr=3$时努塞尔数与$Ra^{0.077}$成比例增长，当$Pr=10$时努塞尔数与$Ra^{0.19}$成比例增长。与托卡马克等离子体的类比。
英文摘要：
We report on direct numerical simulations of two-dimensional, horizontally periodic Rayleigh-Bénard convection, focusing on its ability to drive large-scale horizontal flow that is vertically sheared. For the Prandtl numbers ($Pr$) between 1 and 10 simulated here, this large-scale shear can be induced by raising the Rayleigh number ($Ra$) sufficiently, and we explore the resulting convection for $Ra$ up to $10^{10}$. When present in our simulations, the sheared mean flow accounts for a large fraction of the total kinetic energy, and this fraction tends towards unity as $Ra\to\infty$. The shear helps disperse convective structures, and it reduces vertical heat flux; in parameter regimes where one state with large-scale shear and one without are both stable, the Nusselt number of the state with shear is smaller and grows more slowly with $Ra$. When the large-scale shear is present with $Pr\lesssim2$, the convection undergoes strong global oscillations on long timescales, and heat transport occurs in bursts. Nusselt numbers, time-averaged over these bursts, vary non-monotonically with $Ra$ for $Pr=1$. When the shear is present with $Pr\gtrsim3$, the flow does not burst, and convective heat transport is sustained at all times. Nusselt numbers then grow roughly as powers of $Ra$, but the growth rates are slower than any previously reported for Rayleigh-Bénard convection without large-scale shear. We find the Nusselt numbers grow proportionally to $Ra^{0.077}$ when $Pr=3$ and to $Ra^{0.19}$ when $Pr=10$. Analogies with tokamak plasmas are described.
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