Effect of plumes on measuring the large scale circulation in turbulent Rayleigh-Bénard convection
Effect of plumes on measuring the large scale circulation in turbulent Rayleigh-Bénard convection
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DOI：
10.1063/1.3620999
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发表时间：
2011-09
影响因子：
4.6
通讯作者：
R. Stevens;H. Clercx;D. Lohse
中科院分区：
文献类型：
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作者：
R. Stevens;H. Clercx;D. Lohse
利用直接数值模拟的结果，研究了湍流Rayleigh-Benard(RB)对流中大尺度环流(LSC)的特性。LSC取向由余弦或多项式来确定，它与用探头测量的方位向温度或方位向垂直速度分布相匹配。我们研究了Γ=D/L=1/2和Γ=1，其中D为直径，L为高度的LSC。对于Pr=6.4Ra=1×10~8和5×10~8的长宽比Γ=1的样品，无论是每个水平面只考虑8个探头的数据，还是考虑所有的LSC探头的数据，所得到的LSC取向都是相同的。在Ra=1×108时，Γ=1/2，Pr=0.7时，羽流对方位向温度和方位向垂直速度分布的影响较大。由于通过羽流和/或角流，使用余弦拟合得到的LSC视方向可能会导致对大尺度流动特征的误解。为了进一步量化大尺度流动，我们引入了相对LSC强度，定义为第一傅立叶模的能量与由方位向温度和方位向垂直速度剖面确定的所有模的能量之比。对于Ra=1×108时，我们发现Γ=1/2样本的相对最小二乘法强度明显低于Γ=1的样本，这反映了最小二乘法在Γ=1的样本中比在Γ=1/2的样本中要明显得多。LSC相对强度的确定可直接用于高瑞利数热对流和旋转RB对流的研究。
We studied the properties of the large-scale circulation (LSC) in turbulent Rayleigh-Benard (RB) convection by using results from direct numerical simulations in which we placed a large number of numerical probes close to the sidewall. The LSC orientation is determined by either a cosine or a polynomial fit to the azimuthal temperature or azimuthal vertical velocity profile measured with the probes. We study the LSC in Γ = D/L = 1/2 and Γ = 1 samples, where D is the diameter and L is the height. For Pr = 6.4 in an aspect ratio Γ = 1 sample at Ra = 1 × 108 and 5 × 108, the obtained LSC orientation is the same, irrespective of whether the data of only 8 or all 64 probes per horizontal plane are considered. In a Γ = 1/2 sample with Pr = 0.7 at Ra = 1 × 108, the influence of plumes on the azimuthal temperature and azimuthal vertical velocity profiles is stronger. Due to passing plumes and/or the corner flow, the apparent LSC orientation obtained using a cosine fit can result in a misinterpretation of the character of the large-scale flow. We introduce the relative LSC strength, which we define as the ratio between the energy in the first Fourier mode and the energy in all modes that can be determined from the azimuthal temperature and azimuthal vertical velocity profiles, to further quantify the large-scale flow. For Ra = 1 × 108, we find that this relative LSC strength is significantly lower in a Γ = 1/2 sample than in a Γ = 1 sample, reflecting that the LSC is much more pronounced in a Γ = 1 sample than in a Γ = 1/2 sample. The determination of the relative LSC strength can be applied directly to available experimental data to study high Rayleigh number thermal convection and rotating RB convection