Laboratory Measurements on Turbulent Pressure Fluctuations in and above Gravel Beds
Laboratory Measurements on Turbulent Pressure Fluctuations in and above Gravel Beds
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砾石层内及上方湍流压力脉动的实验室测量
DOI：
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发表时间：
2010
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通讯作者：
G. Jirka
中科院分区：
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作者：
M. Detert;V. Weitbrecht;G. Jirka
通过室内水槽实验，研究了三种多孔颗粒床（砾石床溪流、河流和人工运河）上面和里面的压力波动统计。测试的流动条件包括多种流体动力载荷，这些载荷不断增加，直至单个颗粒不时移动，而不会对床层结构和压力传感器的相关位置造成严重影响。通过直方图和光谱技术以及垂直强度剖面进行分析。得到了两个简化方程，分别描述了测得的阻力波动和升力波动的标准差的垂直减小，它们不受平均床层剪应力的量纲化。前者的波动可以用粗略的线性拟合来描述，而后者则清楚地表明，在多孔床层中，抬升强度呈指数下降，衰减距离为等效颗粒粗糙度的一到两倍。在次表层内，标准偏差达到非零常数，主要受外流中对流的长波压力场支配。这些发现可以用于未来的泥沙输运模型，该模型使用力平衡方法来确定初始运动条件。
The statistics of pressure fluctuations above and within three types of porous granular beds such as in gravel bed streams, rivers, and man-made canals are investigated by data gained via laboratory flume experiments. The flow conditions examined include a diversity of hydrodynamic loads that increase up to the point where single grains are moving from time to time, without causing severe modification to the bed texture and the related positions of the pressure sensors. Analysis is performed by means of histograms and spectral techniques and vertical intensity profiles. Two simplified equations are found that describe the vertical decrease for the standard deviation of the measured fluctuations indicating drag and lift, respectively, nondimensionalized by the mean bed shear stress. The former fluctuation is described by a crude linear fit, whereas the latter clearly shows that the lift intensity decreases exponentially in the porous bed with a decay distance of one to two times the equivalent grain roughness. Within the subsurface layer the standard deviation reaches a nonzero constant, mainly dominated by long-wave pressure fields that are convected in the outer flow. These findings can be used in future sediment transport models that use force balance approaches to determine incipient motion conditions.