中文摘要：

利用高频粒子图像测速PIV（ParticleImageVelocimetry）系统对明渠弯道水流进行了测量，在两种不同试验方式的配合下，不仅提供了大量高精度的平面二维流场数据，还成功重构了弯道水流的三维平均流速场，为深入研究弯道水流复杂的时均流动结构提供了试验依据。试验结果表明，由于弯道曲率不连续，水流主流区在弯道人口位于凸岸附近，随后在离心力的作用下逐渐转移至凹岸，并一直维持至弯道出口；凹岸顶托及环流运动导致不同横向位置处的纵向流速剖面近床面区域速度梯度及最大流速的位置沿程发生改变；弯道曲率越大，最大水深平均纵向流速转移至靠近凹岸一侧的位置离弯道入口越远；受上游直段二次流的影响，环流运动在弯道人口断面呈三涡结构，随后快速衰减为双涡结构；弯道主环流的强度沿程先增加后减小，涡核位置沿程往复摆动。

英文摘要：

Measurement of open-channel-flow in a bend was made by using particle image velocimetry to get instantaneous two-dimensional velocity data based on which the mean, three-dimensional flow fields were reconstructed. The results show the main flow deviates to the convex bank upon entering the bend, then quickly shifts to the concave bank due to centrifugal force and remains near the concave bank until the end of the bend. Velocity gradient near the bed and location of the maximum velocity of the streamwise mean velocity profiles at each transverse location keep chan- ging along the bend due to the action of concave bank lockup and secondary flow. Distance between bend entrance and the section in which the maximum depth-averaged streamwise velocity approach the concave bank increases with the curvature of the bend flume. There exist three-vortex structure in each section near the bend entrance affected by the secondary flow in the upstream straight flume, but this quickly decay into two-vortex structures in other sections. Both the strength of the major secondary flow and the location of its core changes along the bend.