Hydrodynamics and turbulence in emergent and sparsely vegetated open channel flow
Hydrodynamics and turbulence in emergent and sparsely vegetated open channel flow
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DOI：
10.1007/s10652-017-9531-2
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发表时间：
2017-05
影响因子：
2.2
通讯作者：
Soumen Maji;D. Pal;P. R. Hanmaiahgari;U. Gupta
中科院分区：
文献类型：
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作者：
Soumen Maji;D. Pal;P. R. Hanmaiahgari;U. Gupta
本研究报告的实验研究的结果表征的湍流水动力学和流量分配的彻底变化的紧急和稀疏植被明渠流。在明渠断面的中心区域设置一个挺水的刚性稀疏植被斑块，沿水流方向和横向沿着具有规则的树干间距。实验在亚临界流动条件下进行，并与声学多普勒测速系统获得的速度测量。植被斑块内及周围的湍流强度、雷诺切应力、湍流动能和涡动变化较大。在任何横截面通过内部的植被补丁，流向速度随流向长度的增加而减小，速度剖面收敛从对数律的线性剖面与斜率增加。植被斑块内的时均横向和垂直速度随流向距离的增加而增加，并从负值收敛到正值。稀疏植被斑块内部的湍流强度大于无植被斑块内部的湍流强度。与植被内部流向速度剖面的变化趋势相似，湍流强度和垂直雷诺切应力剖面也随流向减小。在植被斑块的内部和后缘的下游，湍流动能剖面表现出不规则的波动和最大值发生在外层。流量分布分析证实，稀疏植被斑块在其附近诱导了蛇形流动模式。在前缘处，气流冲向右侧壁，在后缘处，气流转向左手壁。在前缘和后缘之间，流线沿流向和横向沿着以不同的角度呈锯齿形。在前缘的上游和植被斑块的内部，旋涡运动清晰可见，并且旋涡沿流向沿着通道的宽度伸展。
This present study reports the results of an experimental study characterizing thorough variation of turbulent hydrodynamics and flow distribution in emergent and sparsely vegetated open channel flow. An emergent and rigid sparse vegetation patch with regular spacing between stems along the flow and transverse directions was fixed in the central region of the cross-section of open channel. Experiments were conducted in subcritical flow conditions and velocity measurements were obtained with an acoustic Doppler Velocimetry system. Large variations of the turbulence intensities, Reynolds shear stress, turbulent kinetic energy and vortical motions are found in and around the vegetation patch. At any cross-section through the interior of the vegetation patch, streamwise velocity decreases with increase in streamwise length and the velocity profiles converge from the log-law to a linear profile with increasing slope. Time-averaged lateral and vertical velocities inside the vegetation patch increase with increasing streamwise distance and converge from negative values to positive values. Turbulence intensities interior of the sparse vegetation patch are more than those of without the vegetation patch. Similar to the trend of streamwise velocity profiles inside the vegetation, turbulence intensities and longitudinal-normal Reynolds shear stress profile decreases with streamwise direction. In the interior of the vegetation patch and downstream of the trailing edge, turbulent kinetic energy profiles are exhibiting irregular fluctuations and the maximum values are occurring in the outer layer. Analysis of flow distribution confirms sparse vegetation patch is inducing a serpentine flow pattern in its vicinity. At the leading edge, flow is rushing towards the right hand sidewall, and at the trailing edge, flow is turning to the left hand sidewall. In between the leading and trailing edges, the streamlines are following a zig-zag fashion at varied degree along the streamwise and lateral directions. Immediate upstream of the leading edge and in the interior of the vegetation patch, vortex motion is clearly visible and the vortices are stretched along the width of the channel with streamwise direction.