CONDITIONAL STATISTICS OF REYNOLDS STRESS IN ROUGH-WALL AND SMOOTH-WALL TURBULENT BOUNDARY-LAYERS
CONDITIONAL STATISTICS OF REYNOLDS STRESS IN ROUGH-WALL AND SMOOTH-WALL TURBULENT BOUNDARY-LAYERS
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DOI：
10.1017/s0022112081002164
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发表时间：
1981-01-01
影响因子：
3.7
通讯作者：
RAUPACH, MR
中科院分区：
文献类型：
--
作者：
RAUPACH, MR
象限分析已用于研究在几种不同密度的规则排列的粗糙表面和光滑表面上的零压力梯度湍流边界层中导致雷诺剪切应力的事件。通过将应力划分为喷射、扫掠以及向内和向外的相互作用，结果表明扫掠占靠近粗糙表面的大部分应力，并且扫掠分量的相对大小随着表面粗糙度和与表面的接近而增加。扫掠主导区域描绘了一个“粗糙度子层”，其深度高达几个粗糙度元素高度，其中湍流特性明确取决于粗糙度。在内层（或恒定应力）层的其余部分以及外层中，流动在表面粗糙度方面遵循熟悉的相似定律。扫掠和喷射对应力的分数贡献之间的差异 ΔS0 与流向和法向速度脉动的三阶矩到处都有很好的相关性。在三次矩和 δS0 之间建立了实验比例，并且结果表明与累积量丢弃理论的预测一致。假设大型相干结构通过固定点 T 的时间尺度与瞬时应力 u'w' 的指定象限中出现的平均时间成正比，该瞬时应力 u'w' 至少为局部平均应力 u'w' 的 H 倍，其中 H 是阈值水平。对于喷射象限和扫掠象限以及对于 H 的任何选择，我们发现 T 与摩擦速度 u* 和边界层厚度 δ 成比例，使得 Tu*/δ 不随表面粗糙度的变化而变化。
Quadrant analysis has been used to investigate the events contributing to the Reynolds shear stress in zero-pressure-gradient turbulent boundary layers over regularly arrayed rough surfaces of several different densities, and over a smooth surface. By partitioning the stress into ejections, sweeps, and inward and outward interactions, it is shown that sweeps account for most of the stress close to rough surfaces, and that the relative magnitude of the sweep component increases both with surface roughness and with proximity to the surface. The sweep-dominated region delineates a ‘roughness sublayer’ with a depth of up to several roughness element heights, in which the turbulence characteristics depend explicitly on the roughness. In the remainder of the inner (or constant-stress) layer, and in the outer layer, the flow obeys familiar similarity laws with respect to surface roughness.The difference ΔS0 between the fractional contributions of sweeps and ejections to the stress is shown to be well related everywhere to the third moments of the streamwise and normal velocity fluctuations. Experimental proportionalities are established between the third moments and δS0, and are shown to agree with predictions made from cumulant-discard theory.The time scale for the passage of large coherent structures past a fixed point, T, is assumed proportional to the mean time between occurrences in a specified quadrant of an instantaneous stress u'w’ at least H times the local mean stress u'w’, where H is a threshold level. For both the ejection and sweep quadrants and for any choice of H, it is found that T scales with the friction velocity u* and the boundary-layer thickness δ, such that Tu*/δ is invariant with change of surface roughness.