The motive behind the present paper is to investigate a method for representing the effect of surface roughness in eddy resolving simulations of turbulent flow, without including the geometric form of the roughness as a boundary. It is found that introducing a drag force, quadratic in a reference velocity, and confined to a zone next to the wall, is remarkably possible to capture the dominant effects of roughness. The drag representation is not new; indeed, it is motivated by Reynolds averaged models. The present assessment provides a new perspective on the fluid dynamical action of distributed roughness: its dominant effect is not to create eddies in the wake of asperities, or to provide a geometric obstruction. The drag model, with no geometrical features, suppresses streaks that occur over smooth walls, and generates large, outer region eddies, in a quite similar way to resolved roughness. In a sense, this is an expanded perspective on Townsend’s hypothesis. As in that hypothesis, Reynolds stresses scale on friction velocity; but, expanding on the original hypothesis, spectra over the forcing layer agree closely with those over resolved roughness, when the force is calibrated to produce the same friction Reynolds number as the resolved roughness.

中文翻译：

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在涡流解析模拟中表示表面粗糙度

本文背后的动机是研究一种在湍流的涡流解析模拟中表示表面粗糙度影响的方法，而不包括粗糙度的几何形式作为边界。研究发现，引入一个与参考速度成二次方的阻力并限制在靠近壁的区域，非常有可能捕捉粗糙度的主要影响。拖动表示并不新鲜；事实上，它是由雷诺平均模型驱动的。本评估为分布式粗糙度的流体动力学作用提供了一个新的视角：其主要影响不是在粗糙后产生涡流，也不是提供几何障碍。没有几何特征的阻力模型抑制了光滑壁上出现的条纹，并生成大的外部区域涡流，以非常相似的方式解决粗糙度。从某种意义上说，这是对汤森假设的扩展视角。在那个假设中，雷诺兹强调摩擦速度的比例；但是，扩展最初的假设，当力被校准以产生与解析的粗糙度相同的摩擦雷诺数时，强迫层上的光谱与那些过度解析的粗糙度非常吻合。