在紊流瑞利-贝纳德对流中缺乏慢瞬变和不完全垂直排列的影响
Absense of slow transients, and the effect of imperfect vertical alignment, in turbulent Rayleigh-Benard convection
摘要：
我们报告的实验结果的倾斜角β相对于重力对湍流瑞利-贝纳德对流的圆柱形样品的影响。测量是在瑞利数R达到10^11时进行的，其中两个样品的高度L等于直径D（纵横比Gamma = D/L = 1）。流体是水，普朗特数σ = 4.38。与Chilla et.对于类似的样品，但γ = 0.5（D = 0.5和L = 1.0 m），我们发现没有长的弛豫时间。当R = 9.4 × 10^10时，我们测量了努塞尔数N作为倾角β的函数，得到了一个小的β依赖关系，比奇拉等人的结果小50倍。（2004），其Gamma = 0.5样本。我们测量了样品水平中平面上八个等距方位角位置的侧壁温度，并使用它们的交叉关联函数来确定大尺度环流（LSC）的翻转时间。结果表明，雷诺数R_e^cc随β的增大而增大。一个重要的结论是，随着LSC的β的增加，R_e^cc对热传输没有显著影响。在10 ^9 < R <10 ^11的范围内，由于倾斜而在恒定β下增加的R_e^cc可以用指数为-1/6的R的幂律来描述，这与一个简单的模型相一致，该模型通过跨越边界层的剪切应力来平衡由于倾斜角而产生的附加浮力。即使是一个小的倾斜角显着抑制的方位角曲折和突然的重定向特性的LSC在一个样本与β = 0。在我们的分辨率范围内，水平中平面处的温度的方位平均值与β无关。
英文摘要：
We report experimental results for the influence of a tilt angle beta relative to gravity on turbulent Rayleigh-Benard convection of cylindrical samples. The measurements were made at Rayleigh numbers R up to 10^11 with two samples of height L equal to the diameter D (aspect ratio Gamma = D/L = 1). The fluid was water with a Prandtl number sigma = 4.38. In contrast to the experiences reported by Chilla et. al. (2004) for a similar sample but with Gamma = 0.5 (D = 0.5 and L = 1.0 m), we found no long relaxation times. For R = 9.4 times 10^10 we measured the Nusselt number N as a function of tilt angle beta and obtained a small beta dependence about a factor of 50 smaller than the result found by Chilla et. al. (2004) for their Gamma = 0.5 sample. We measured side-wall temperatures at eight equally spaced azimuthal locations on the horizontal mid-plane of the sample and used their cross-correlation functions to find the turn-over time of the large-scale circulation (LSC). The resulting Reynolds numbers R_e^cc were found to increase with beta. An important conclusion is that the increase of R_e^cc with beta of the LSC does not significantly influence the heat transport. Over the range 10^9 < R < 10^11 the enhancement of R_e^cc at constant beta due to the tilt could be described by a power law of R with an exponent of -1/6, consistent with a simple model that balances the additional buoyancy due to the tilt angle by the shear stress across the boundary layers. Even a small tilt angle dramatically suppressed the azimuthal meandering and the sudden reorientations characteristic of the LSC in a sample with beta = 0. The azimuthal mean of the temperature at the horizontal mid-plane within our resolution was independent of beta.
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