Free surface flow over square bars at intermediate relative submergence
Free surface flow over square bars at intermediate relative submergence
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DOI：
10.1080/00221686.2017.1413601
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发表时间：
2018-03
影响因子：
2.3
通讯作者：
R. McSherry;K. Chua;T. Stoesser;S. Mulahasan
中科院分区：
文献类型：
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作者：
R. McSherry;K. Chua;T. Stoesser;S. Mulahasan
本文给出了中淹没条件下床面方坝明渠紊流的大涡模拟和补充水槽试验结果。研究了具有两个杆间距、对应于过渡粗糙度和k型粗糙度、以及三种流速的情况。在平均自由面高程和平均流向速度方面，模拟结果与实验结果吻合较好。给出了模拟的时间平均流向、流函数和湍动能等值线，揭示了粗糙度几何形状对水面响应的影响。对流速度垂直分布的分析表明，在最低淹没情况下，不存在对数层，而在较高淹没情况下，观察到一些这样的对数层。对于一些水流，观测到了中度到显著的水面变形，包括微弱的和/或起伏的水力跳跃，这对整个流向动量平衡有很大影响。根据动量平衡分析了雷诺剪应力、形状诱导应力和形状阻力，以评估它们对这些流动总水力阻力的贡献。结果表明，在水面上，形状诱导应力占主导地位，对总阻力的贡献很大，但由于杆件的存在，所有情况下的总阻力都是由形状阻力决定的。
ABSTRACT Results from large-eddy simulations and complementary flume experiments of turbulent open channel flows over bed-mounted square bars at intermediate submergence are presented. Scenarios with two bar spacings, corresponding to transitional and k-type roughness, and three flow rates, are investigated. Good agreement is observed between the simulations and the experiments in terms of mean free surface elevations and mean streamwise velocities. Contours of simulated time-averaged streamwise, streamfunction and turbulent kinetic energy are presented and these reveal the effect of the roughness geometry on the water surface response. The analysis of the vertical distribution of the streamwise velocity shows that in the lowest submergence cases no logarithmic layer is present, whereas in the higher submergence cases some evidence of such a layer is observed. For several of the flows moderate to significant water surface deformations are observed, including weak and/or undular hydraulic jumps which affect significantly to the overall streamwise momentum balance. Reynolds shear stress, form-induced stress and form drag are analysed with reference to the momentum balance to assess their contributions to the total hydraulic resistance of these flows. The results show that form-induced stresses are dominant at the water surface and can contribute significantly to the overall drag, but the total resistance in all cases is dominated by form drag due to the presence of the bars.