摘要
为揭示散粒粗糙床面的当量糙率尺度特征,采用4种散粒粗糙床面开展了8组粒子图像测速法(PIV)水槽明渠紊流试验,探讨了理论床面位置、当量糙率尺度和阻力系数的沿程分布规律,分析了当量糙率尺度与阻力系数的内在关系。结果表明:(1)散粒粗糙床面明渠水流特性沿程可分为颗粒区和粒间区,各区的理论床面位置参数ξ、相对当量糙率尺度k_(s0)和阻力系数f具有显著差异,颗粒区0. 65≤ξ≤0. 85,k_(s0)波动明显,f较大;粒间区ξ=1,k_(s0)变化相对平缓,f较小。(2) k_(s0)沿程平均值与颗粒直径d成正比,与排列间距Lx及水流雷诺数Re成反比,在d、Lx及Re相同时,梅花形排列的k_(s0)大于矩形排列。(3) f随k_(s0)呈递增变化,变化特性与相对光滑度h/d密切相关。研究成果可为散粒粗糙床面沿程阻力系数确定提供科学参考。
To investigate the distribution characteristics of the equivalent roughness of open-channel flow over an array of glass spheres, eight groups of open-channel turbulence experiments were performed with four different rough beds. The instantaneous velocity data were obtained through particle-image velocimetry (PIV) along the longitudinal cross-section of the test flume. From an analysis of the experimental data, the longitudinal distributions of the theoretical position of the bed surface, equivalent roughness, and coefficient of drag were obtained, and the intrinsic relationship between equivalent roughness and the coefficient of drag was determined. The result shows that the characteristics of the flow in a coarse-grained open channel distinguish two regions, one spherical and the other inter-spherical. There are significant differences in the theoretical position of the bed surface ξ, the relative equivalent roughness ks0, and the coefficient of drag f in each region. In the spherical region (0.65 ≤ ξ ≤ 0.85), a fluctuation in ks0 is evident, and the value of f is large, whereas in the inter-sphere region (ξ=1), the fluctuation in ks0 is relatively slow, and the value of f is small. Another difference is that the average value of ks0 is proportional to the diameter d of the sphere and inversely proportional to the array spacing Lx and the Reynolds number Re of the flow. When the diameter, array spacing, and Reynolds number are fixed, the average value of ks0 for a quincunx-arrayed bed is greater than that of the rectangular-arrayed bed. Moreover, the coefficient of drag increases with ks0, and the variation in the flow characteristics are closely related to the relative smoothness h/d. These results provide a quantitative reference for the determination of the coefficient of drag for open-channel flows over a rough surface.
作者
钟亮
廖尚超
张建梅
孙建云
倪志辉
ZHONG Liang;LIAO Shangchao;ZHANG Jianmei;SUN Jianyun;NI Zhihui(National Engineering Research Center for Inland Waterway Regulation,Chongqing Jiaotong University,Chongqing 400074,China;Key Laboratory of Hydraulic and Waterway Engineering of the Ministry of Education,Chongqing Jiaotong University,Chongqing 400074,China;Southwestern Research Institute of Water Transportation Engineering,Chongqing Jiaotong University,Chongqing 400016,China)
出处
《水科学进展》
EI
CAS
CSCD
北大核心
2018年第6期865-876,共12页
Advances in Water Science
基金
国家自然科学基金资助项目(51509026)
重庆市基础科学与前沿技术研究项目(cstc2017jcyjAx0278).
关键词
散粒粗糙床面
明渠紊流
摩阻流速
理论床面
当量糙率尺度
阻力系数
bed with roughness array
open-channel turbulence
friction velocity
theoretical bed surface
equivalent roughness
coefficient of drag
