Direct numerical simulation of turbulent channel flow over a surrogate for Nikuradse-type roughness
Direct numerical simulation of turbulent channel flow over a surrogate for Nikuradse-type roughness
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DOI：
10.1017/jfm.2017.873
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发表时间：
2017-12
影响因子：
3.7
通讯作者：
M. Thakkar;Angela Busse;N. Sandham
中科院分区：
文献类型：
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作者：
M. Thakkar;Angela Busse;N. Sandham
采用平铺方法模拟粗糙表面，研究了从流体动力光滑极限情况到完全粗糙条件下粗糙度雷诺数的全范围。该表面基于标准喷砂比较仪的扫描，随后进行低通滤波，并使其具有空间周期性。高粗糙度雷诺数是通过增加直接数值模拟中的摩擦雷诺数来获得的，而低粗糙度雷诺数是通过缩小表面和平铺来保持区域尺寸恒定来获得的。在这两种情况下，都保持了对盒大小、以墙为单位的分辨率和粗糙表面每最小波长分辨率的计算要求。由此得到的粗糙度函数行为重复了Nikuradse(1933 VDI-Forschungsheft，Vol.361)的实验，表明处理后的喷砂表面可以作为他的砂粒粗糙度的替代，其精确结构尚无文献记载。本文的模拟还证明了与流体动力光滑壁面结果的单调偏离，该结果符合几何关系，其指数与Colebrook公式和早期基于低雷诺数阻力关系的理论论证都不一致。
A tiled approach to rough surface simulation is used to explore the full range of roughness Reynolds numbers, from the limiting case of hydrodynamic smoothness up to fully rough conditions. The surface is based on a scan of a standard grit-blasted comparator, subsequently low-pass filtered and made spatially periodic. High roughness Reynolds numbers are obtained by increasing the friction Reynolds number of the direct numerical simulations, whereas low roughness Reynolds numbers are obtained by scaling the surface down and tiling to maintain a constant domain size. In both cases, computational requirements on box size, resolution in wall units and resolution per minimum wavelength of the rough surface are maintained. The resulting roughness function behaviour replicates to good accuracy the experiments of Nikuradse (1933 VDI-Forschungsheft, vol. 361), suggesting that the processed grit-blasted surface can serve as a surrogate for his sand-grain roughness, the precise structure of which is undocumented. The present simulations also document a monotonic departure from hydrodynamic smooth-wall results, which is fitted with a geometric relation, the exponent of which is found to be inconsistent with both the Colebrook formula and an earlier theoretical argument based on low-Reynolds-number drag relations.