A wind-tunnel boundary-layer study of the effects of a surface roughness change: Rough to smooth
A wind-tunnel boundary-layer study of the effects of a surface roughness change: Rough to smooth
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表面粗糙度变化影响的风洞边界层研究：从粗糙到平滑
DOI：
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发表时间：
1978
期刊：
影响因子：
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通讯作者：
P. Mulhearn
中科院分区：
文献类型：
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作者：
P. Mulhearn
在风洞中模拟了由于表面粗糙度从非常粗糙到光滑的突然变化而对低层大气中平均速度和湍流统计造成的变化。还研究了有效表面水平的变化的影响，这往往伴随着这样的表面粗糙度的变化。在变化的上游产生了一个深湍流，在地板上方约200 mm处具有对数平均速度分布和恒定的剪切应力，除了表面附近的区域受到随机粗糙表面的三维性质的影响。当表面粗糙度变化与表面水平变化一致时，靠近表面的下游流处于上游粗糙元件的尾流中，测量的雷诺剪应力值低于下游表面升高时获得的值。在所有情况下，雷诺剪应力随内层下部三分之二的高度近似线性变化，在表面附近没有明显的恒定应力区，甚至在粗糙度变化下游2 m处也没有。当粗糙度的变化并不伴随着水平的变化时，雷诺剪应力值外推到表面同意以及从“壁律”推断的表面剪应力。垂直和横向速度波动的均方变化和积分时间尺度，作为流通过下游的粗糙度变化，是令人惊讶的小。
The changes imposed on mean velocities and turbulence statistics in the lower atmosphere by an abrupt change in surface roughness, from very rough to smooth, were modelled in a wind tunnel. The influence of a change in the effective surface level, which often accompanies such a variation in surface roughness, was also studied. A deep, turbulent flow was generated upstream of the change, which had a logarithmic mean velocity profile and constant shear-stress for approximately 200 mm above the floor, except for a region near the surface which was influenced by the three-dimensional nature of the random rough surface.When the surface roughness change coincided with a change in surface level, the downstream flow close to the surface was in the wake of the upstream roughness elements, and measured Reynolds shear-stress values were lower than those obtained when the downstream surface was raised. Otherwise, the influence of a change in surface level was small.In all cases, Reynolds shear-stress varied approximately linearly with height in the lower two-thirds of the internal layer and no constant stress region was apparent near the surface, even 2 m downstream of the roughness change. When the roughness change was not accompanied by a change in level, Reynolds shear-stress values extrapolated to the surface agreed well with surface shear-stress inferred from the ‘law of the wall’.Changes in mean squares of vertical and lateral velocity fluctuations and in integral time scales, as the flow passed downstream of the roughness change, were surprisingly small.