论文标题
湍流在过渡性粗糙的表面上，粗糙度密度变化
Turbulent flow over transitionally rough surfaces with varying roughness densities
论文作者
论文摘要
我们研究了三维过渡性正弦表面上流的直接数值模拟的粗壁湍流。粗糙度雷诺数固定为$ k^+= 10 $，其中$ k $是正弦的半振幅，正弦波波长变化了，导致粗糙度固体，$λ$（额叶区域除以计划区域），范围为0.05至0.54。 Chung等人最近证明，通过使用最小跨通道技术来解决围绕密集的粗糙度元素和大量流量的高成本。 （J. Fluid Mech。，第773卷，2015年，第418-431页），以准确确定Hama粗糙度函数，$ΔU^+$。观察到在最小和全跨度粗壁通道之间，二阶统计在受壁粗糙度影响区域中的良好一致。在粗糙度稀疏（$λ\ Lessim 0.15 $）中，粗糙度函数随着固体性的增加而增加，而在密集状态下，粗糙度函数随着固体性的增加而降低。发现密集政权始于$λ\ gtrsim0.15- $ 0.18，与文献一致。为$λ\ rightarrow \ infty $的限制提出了一个模型，该$是位于粗糙度元素冠的光滑墙。该模型有助于解释粗糙度的渐近行为，本文中介绍的粗壁数据表明，近壁流量趋向于这种建模的极限。峰值流向湍流强度与湍流近壁周期相关，随着固体性的增加，越来越远离壁的移动。在稀疏政权中，增加$λ$会减少与近壁周期相关的流向动荡的能量，而在密集政权中增加$λ$会增加湍流能源[续] $ \ ldots $
We investigate rough-wall turbulent flows through direct numerical simulations of flow over three-dimensional transitionally rough sinusoidal surfaces. The roughness Reynolds number is fixed at $k^+=10$, where $k$ is the sinusoidal semi-amplitude, and the sinusoidal wavelength is varied, resulting in the roughness solidity, $Λ$ (frontal area divided by plan area) ranging from 0.05 to 0.54. The high cost of resolving both the flow around the dense roughness elements and the bulk flow is circumvented by the use of the minimal-span channel technique, recently demonstrated by Chung et al. (J. Fluid Mech., vol. 773, 2015, pp. 418-431) to accurately determine the Hama roughness function, $ΔU^+$. Good agreement of the second-order statistics in the near-wall roughness-affected region between minimal- and full-span rough-wall channels is observed. In the sparse regime of roughness ($Λ\lesssim 0.15$) the roughness function increases with increasing solidity, while in the dense regime the roughness function decreases with increasing solidity. It was found that the dense regime begins when $Λ\gtrsim0.15-$0.18, in agreement with the literature. A model is proposed for the limit of $Λ\rightarrow\infty$, which is a smooth wall located at the crest of the roughness elements. This model assists with interpreting the asymptotic behaviour of the roughness, and the rough-wall data presented in this paper show that the near-wall flow is tending towards this modelled limit. The peak streamwise turbulence intensity, which is associated with the turbulent near-wall cycle, is seen to move increasingly further away from the wall with increasing solidity. In the sparse regime, increasing $Λ$ reduces streamwise turbulent energy associated with the near-wall cycle, while increasing $Λ$ in the dense regime increases turbulent energy [continued]$\ldots$
