du Puits Ronald, Resagk Christian, Thess André
Department of Mechanical Engineering, Ilmenau University of Technology, PO Box 100565, 98684 Ilmenau, Germany.
Phys Rev E Stat Nonlin Soft Matter Phys. 2009 Sep;80(3 Pt 2):036318. doi: 10.1103/PhysRevE.80.036318. Epub 2009 Sep 30.
Highly resolved profiles of the mean velocity in turbulent Rayleigh-Bénard convection in air are presented and discussed. The present work extends our recently performed experiments at constant aspect ratio [Phys. Rev. Lett. 99, 234504 (2007)] to variable aspect ratios. The experiments cover a range of Rayleigh numbers 10(9)<Ra<10(12) and aspect ratios 1.13<Gamma<11.3 whereas the Prandtl number is fixed at Pr=0.7. The major finding of the present work is that the profiles of the mean horizontal velocity and its fluctuations are virtually invariant against the variation in Ra or Gamma if the wall distance is scaled by the displacement thickness of the boundary layer. Furthermore we have studied typical length scales of the boundary layer and their scaling with Ra and Gamma. Regarding a potential transition of the heat transport toward the ultimate regime we found that the boundary layer Reynolds number remains below Redelta=250 which is significantly lower than the predicted limit.
本文给出并讨论了空气湍流瑞利 - 贝纳德对流中平均速度的高分辨率分布。目前的工作将我们最近在恒定纵横比下进行的实验[《物理评论快报》99, 234504 (2007)]扩展到了可变纵横比。实验涵盖了一系列瑞利数10(9)<Ra<10(12)和纵横比1.13<Gamma<11.3，而普朗特数固定为Pr = 0.7。当前工作的主要发现是，如果壁面距离按边界层的位移厚度进行缩放，平均水平速度及其波动的分布实际上与Ra或Gamma的变化无关。此外，我们研究了边界层的典型长度尺度及其与Ra和Gamma的标度关系。关于热传输向最终状态的潜在转变，我们发现边界层雷诺数保持在Redelta = 250以下，这明显低于预测极限。
