大尺度糙率条件下流速分布规律的试验与理论研究  

Experimental and theoretical study of velocity profiles affected by large-scale roughness

作　　者：徐璞儿 程年生 魏茂兴 Pu-er Xu;Nian-sheng Cheng;Mao-xing Wei(Ocean College,Zhejiang University,Zhoushan 316021,China)

机构地区：[1]浙江大学海洋学院,舟山316021

出　　处：《水动力学研究与进展（A辑）》2022年第5期633-638,共6页Chinese Journal of Hydrodynamics

基　　金：国家自然科学基金(519792442,52109103)。

摘　　要：大尺度糙率条件下,床面糙率对水流特性的影响不再局限于近床区域,而会传播至包括自由表面的整个水深,这将导致被广泛认可的对数型流速分布规律不再适用。为避免自由表面对流场测量的影响,该文选用矩形断面粗糙管开展大尺度糙率水流试验。首先采用粒子图像测速技术(PIV)进行二维流场测量,并对实测流速的垂线分布进行了时间和空间的双平均处理;然后基于Prandtl紊流掺混理论,假设掺混长度为常数,推导出指数型流速分布公式。结果表明,理论公式与试验资料吻合良好,说明所采用的假设较好地描述了大尺度糙率水流的扩散特性。试验结果还表明,受大糙率元的影响,紊动强度和雷诺切应力的峰值位置明显偏离床面,紊动强度沿水深的分布趋向均匀。The effect of large-scale roughness on flow characteristics is no longer restricted to the near-bed area. It may extend to the entire flow domain, including the free surface, rendering the widely used logarithmic velocity law inapplicable. In order to avoid free surface effects, experiments are carried out in a rectangular closed-channel with rough bed. The twodimensional flow field is measured by particle image velocimetry(PIV), and the measured velocity profiles are processed using the double-averaging method. By applying Prandtl’s mixing length theory and assuming the mixing length to be constant, a power-law velocity formula is derived. The results of theoretical formula are in good agreement with the experimental data,indicating that the adopted assumption can well describe the diffusion characteristics of flows subjected to large-scale roughness.Results also show that the large-scale roughness causes that the peak positions of turbulence intensity and Reynolds shear stress deviate significantly from the bed surface, and the vertical distribution of turbulence intensities tends to be uniform.

关 键 词：紊流 矩形管道 大尺度糙率 流速分布 

分 类 号：TV139.2[水利工程—水力学及河流动力学]