Reynolds and dispersive shear stress contributions above highly skewed roughness
Reynolds and dispersive shear stress contributions above highly skewed roughness
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雷诺和分散剪切应力对高度倾斜粗糙度的贡献
DOI：
10.1017/jfm.2018.541
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发表时间：
2018
影响因子：
3.7
通讯作者：
Jelly T
中科院分区：
文献类型：
--
作者：
Jelly T
采用直接数值模拟方法研究了充分发展的槽道湍流中不规则峰和/或坑占主导地位的表面诱导的粗糙度函数。一个表面生成算法被用来合成一个不规则的高斯高度图与周期性的边界。高斯高度图被分解成“仅凹坑”和“仅峰值”分量，这产生了两个具有相似统计特性的附加表面，除了偏斜度，它们是相等和相反的。虽然只有峰的表面产生的粗糙度函数与高斯表面的粗糙度函数相当，但只有坑的表面表现出弱得多的粗糙度效应。结果的分析是辅助推导出一个方程的粗糙度函数，定量识别的动量损失和/或增益的机制。“形式引起的”和随机流体运动的粗糙度函数的统计贡献进行了研究，进一步详细使用象限分析。高斯和峰值只有表面上，色散和雷诺剪应力的贡献表现出补偿效果，而上面的凹坑只有表面上，观察到的添加剂的效果。总体而言，结果强调的敏感性，近壁流相对于高阶地形参数，这反过来又会引起显着差异的粗糙度函数以上的峰值和/或坑为主的表面。
The roughness functions induced by irregular peak- and/or pit-dominated surfaces in a fully developed turbulent channel flow are studied by direct numerical simulation. A surface generation algorithm is used to synthesise an irregular Gaussian height map with periodic boundaries. The Gaussian height map is decomposed into ‘pits-only’ and ‘peaks-only’ components, which produces two additional surfaces with similar statistical properties, with the exception of skewness, which are equal and opposite . While the peaks-only surface yields a roughness function comparable to that of the Gaussian surface, the pits-only surface exhibits a far weaker roughness effect. Analysis of results is aided by deriving an equation for the roughness function that quantitatively identifies the mechanisms of momentum loss and/or gain. The statistical contributions of ‘form-induced’ and stochastic fluid motions to the roughness function are examined in further detail using quadrant analyses. Above the Gaussian and peaks-only surfaces, the contributions of dispersive and Reynolds shear stresses show a compensating effect, whereas above the pits-only surface, an additive effect is observed. Overall, the results emphasise the sensitivity of the near-wall flow with respect to higher-order topographical parameters, which can, in turn, induce significant differences in the roughness function above a peak- and/or pit-dominated surface.
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