Abstract Large Eddy Simulations (LES) are carried out to investigate on the mean flow in turbulent channel flows over irregular rough surfaces. Here the attention is focused to selectively investigate on the effect induced by crests or cavities of the roughness. The irregular shape is generated through the super-imposition of sinusoidal functions having random amplitude and four different wave-lengths. The irregular roughness profile is reproduced along the spanwise direction in order to obtain a 2D rough shape. The analysis of the mean velocity profiles shows that roughness crests induce higher effect in the outer-region whereas roughness cavities cause the highest effects in the inner-region with a reduced effect in the external region. The numerical simulations have been carried out at friction Reynolds number Reτ=395. Similar results have been found for the higher order statistics: turbulence intensities or shear stresses. The analysis of the Reynolds stress anisotropy tensor confirms the existence of specific roles of cavities and crests in the turbulence modulation.

中文翻译：

---

不规则粗糙度形状对湍流通道流动影响的大涡模拟

摘要 进行大涡模拟（LES）以研究不规则粗糙表面上湍流通道流动中的平均流动。这里的注意力集中在有选择地研究由粗糙度的波峰或空腔引起的影响。不规则形状是通过叠加具有随机幅度和四种不同波长的正弦函数产生的。沿展向方向再现不规则的粗糙度轮廓以获得二维粗糙形状。平均速度剖面的分析表明，粗糙度波峰在外部区域引起更大的影响，而粗糙度腔在内部区域引起最高影响，而在外部区域引起的影响较小。数值模拟是在摩擦雷诺数 Reτ=395 下进行的。对于更高阶的统计数据也发现了类似的结果：湍流强度或剪切应力。雷诺应力各向异性张量的分析证实了空腔和波峰在湍流调制中的特定作用的存在。