A note on “critical roughness height” and “transitional roughness”
A note on “critical roughness height” and “transitional roughness”
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关于“临界粗糙度高度”和“过渡粗糙度”的注释
DOI：
10.1063/1.870410
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发表时间：
2000
影响因子：
4.6
通讯作者：
P. Bradshaw
中科院分区：
文献类型：
--
作者：
P. Bradshaw
一个不严谨但似乎合理的分析表明，临界粗糙度高度的概念是错误的，在这个高度以下，粗糙度不影响湍流壁面流动。Oseen近似意味着粗糙度对壁面对数定律中可加常数的影响应随粗糙度雷诺数的平方而变化（特别是以“壁面单位”表示的粗糙度高度）。这是决定在高单位雷诺数实验中使用的表面是否可以视为水力光滑的重要一点。还应注意Nikuradse在雷诺数的“过渡”范围内对等粒径沙粒粗糙度的管流摩擦系数的测量结果与1944年穆迪图中数据相关性的质的差异；后者源于20世纪30年代对各种真实粗糙表面的测试。几乎所有关于基础流体动力学的教科书都有，但实际上没有一本讨论这种差异。尼古拉兹米……
An unrigorous but plausible analysis suggests that the concept of a critical roughness height, below which roughness does not affect a turbulent wall flow, is erroneous. The Oseen approximation implies that the effect of roughness on the additive constant in the logarithmic law of the wall should vary as the square of the roughness Reynolds number (specifically the roughness height in “wall units”). This is an important point in determining whether surfaces used in experiments at high unit Reynolds number can be regarded as hydraulically smooth. Attention is also called to the qualitative difference between Nikuradse’s measurements of friction factor in pipe flow with uniform-size sand-grain roughness in the “transitional” range of Reynolds number and the data correlation in the Moody chart of 1944; the latter was derived from tests on miscellaneous real-life rough surfaces in the 1930s. Nearly all textbooks on elementary fluid dynamics present, but practically none discuss, this difference. Nikuradse’s m...