Pressure forces on sediment particles in turbulent open-channel flow: a laboratory study
Pressure forces on sediment particles in turbulent open-channel flow: a laboratory study
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DOI：
10.1017/jfm.2014.498
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发表时间：
2014-09
影响因子：
3.7
通讯作者：
M. Amir;V. Nikora;M. Stewart
中科院分区：
文献类型：
--
作者：
M. Amir;V. Nikora;M. Stewart
在实验室大型水槽中，对不同水深、不同坡度的明渠水流床面泥沙颗粒脉动压力进行了试验研究。压力测量是使用23个装有差压传感器的球形颗粒进行的。这些测量与使用高分辨率立体粒子图像测速仪同时测量速度场是相辅相成的。压力统计表明，阻力和升力脉动的标准偏差分别为壁面剪应力的2.0~2.6倍和2.5~3.4倍，并与相对浸没高度和流动雷诺数有关。偏度对阻力波动是正的，对升力波动是负的。阻力和升力波动的峰度值均随颗粒淹没程度的增大而增大。与阻力-阻力和升力-升力的两点关联相比，阻力和升力波动之间的两粒子关联相对较弱。在对流速度为主体流速的0.64~0.72倍时，纵向分离颗粒间的压力互相关关系在一定的时间延迟出现极大值，与近床面涡流对流速度非常接近。阻力波动的时间自相关衰减比升力波动快得多，因此升力波动的时间尺度是阻力波动的3-6倍。阻力和升力波动的空间和时间尺度都表现出对水流深度和河床坡度的依赖性。还评估了阻力和升力波动的频谱行为。一个$\def\xmlpi#1{}\def\mathsfbi#1{\boldsign{\mathsf{#1}\let\le=\leqslant\let\leq=\leqslant\let\ge=\geqslant\let\geq=\geqslant\def\pr{\mathit{pr}}\def\fR{\mathit{fr}}\def\rey{\mathit{re}}f^{-11/3}$斜率是在大部分频率范围内观察到的两个标度范围在高频下遵循一个斜率，在低频下遵循$f^5/3}行为。
Abstract An experimental investigation into the fluctuating pressure acting on sediment particles on the bed of an open-channel flow was carried out in a large laboratory flume for a range of flow depths and bed slopes. The pressure measurements were made using 23 spherical particles instrumented with differential pressure sensors. These measurements were complemented with simultaneous measurements of the velocity field using high-resolution stereoscopic particle image velocimetry. The pressure statistics show that the standard deviations of the drag and lift fluctuations vary from 2.0 to 2.6 and from 2.5 to 3.4 times the wall shear stress, respectively, and are dependent on relative submergence and flow Reynolds number. The skewness is positive for the drag fluctuations and negative for the lift fluctuations. The kurtosis values of both drag and lift fluctuations increase with particle submergence. The two-particle correlation between drag and lift fluctuations is found to be relatively weak compared to the two-point drag–drag and lift–lift correlations. The pressure cross-correlations between particles separated in the longitudinal direction exhibit maxima at certain time delays corresponding to the convection velocities varying from 0.64 to 0.72 times the bulk flow velocity, being very close to the near-bed eddy convection velocities. The temporal autocorrelation of drag fluctuations decays much faster than that for the lift fluctuations; as a result, the temporal scales of lift fluctuations are 3–6 times that of drag fluctuations. The spatial and temporal scales of both drag and lift fluctuations show dependence on flow depth and bed slope. The spectral behaviour of both drag and lift fluctuations is also assessed. A $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}f^{-11/3}$ slope is observed for the spectra of the drag fluctuations over the majority of the frequency range, whereas the lift spectra suggest two scaling ranges, following a $f^{-11/3}$ slope at high frequencies and $f^{-5/3}$ behaviour at lower frequencies.