Experimental study of turbulent oscillatory boundary layers in an oscillating water tunnel
Experimental study of turbulent oscillatory boundary layers in an oscillating water tunnel
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振荡水洞中湍流振荡边界层的实验研究
DOI：
10.1155/2012/376293
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
O. Madsen
中科院分区：
文献类型：
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作者：
Jing Yuan;O. Madsen
高品质的实验研究，包括大量的测试，对应于全尺寸的海岸边界层流进行了使用振荡水洞流生成和粒子图像测速系统的速度测量。正弦，斯托克斯和前倾波超过三个固定的底部粗糙度配置，即光滑，“砂纸”和陶瓷大理石底部进行测试。实验结果表明，对数剖面能较准确地反映近底区的边界层流动，因此对数剖面拟合分析能高精度地确定理论底部位置和底部粗糙度。正弦波和非线性波的一次谐波速度，以及非线性波的二次谐波速度，表现出类似的垂直变化模式。两个无量纲的特征边界层厚度，海拔的1%的速度赤字和海拔的最大振幅，被发现有幂律依赖于粗糙的底部试验的相对粗糙度。一个弱的边界层流嵌入在非线性波和一个小的预印本提交给海岸工程2014年3月25日，但有意义的三次谐波速度嵌入在正弦波观察。它们只能用随时间变化的湍流涡动粘性效应来解释。测得的周期平均垂直速度表明，在测试通道中存在普朗特的第二类二次流。在从流速测量推断底部剪切应力的三种方法中，雷诺应力方法由于错过湍流涡旋而低估了剪切应力，并且动量积分方法由于二次流而显著低估了粗糙底部测试的底部剪切应力，因此仅考虑对数剖面拟合方法来产生正确的估计。分析得到的底部剪应力的最大值和前三个谐波，并使用结果来验证一些现有的理论模型。
A high-quality experimental study including a large number of tests which correspond to full-scale coastal boundary layer flows is conducted using an oscillating water tunnel for flow generations and a Particle Image Velocimetry system for velocity measurements. Tests are performed for sinusoidal, Stokes and forward-leaning waves over three fixed bottom roughness configurations, i.e. smooth, “sandpaper” and ceramic-marble bottoms. The experimental results suggest that the logarithmic profile can accurately represent the boundary layer flows in the very near-bottom region, so the log-profile fitting analysis can give highly accurate determinations of the theoretical bottom location and the bottom roughness. The first-harmonic velocities of both sinusoidal and nonlinear waves, as well as the second-harmonic velocities of nonlinear waves, exhibit similar patterns of vertical variation. Two dimensionless characteristic boundary layer thicknesses, the elevation of 1% velocity deficit and the elevation of maximum amplitude, are found to have power-law dependencies on the relative roughness for rough bottom tests. A weak boundary layer streaming embedded in nonlinear waves and a small Preprint submitted to Coastal Engineering March 25, 2014 but meaningful third-harmonic velocity embedded in sinusoidal waves are observed. They can be only explained by the effect of a time-varying turbulent eddy viscosity. The measured period-averaged vertical velocities suggest the presence of Prandtl’s secondary flows of the second kind in the test channel. Among the three methods to infer bottom shear stress from velocity measurements, the Reynolds stress method underestimates shear stress due to missed turbulent eddies, and the momentum integral method also significantly underestimates bottom shear stress for rough bottom tests due to secondary flows, so only the log-profile fitting method is considered to yield the correct estimate. The obtained bottom shear stresses are analyzed to give the maximum and the first three harmonics, and the results are used to validate some existing theoretical models.