中文摘要：

对180°强弯河道水流结构及离散特性进行了研究。采用三维多普勒超声流速仪（ADV ）对强弯河道5个典型断面的流速场进行了量测，得到了各典型断面上的实测流速资料；进而采用改进的分区模型，分别对强弯河道的横向和纵向离散系数进行了研究。结果表明：在弯道进口段，凹岸附近水流受到限制，流速减小，凸岸附近水流流速增大，纵向剪切流速较大，故纵向离散系数较大，此时二次流尚未形成，横向掺混并不剧烈，所以横向离散系数还比较小。随着水流入弯的不断发展，弯道内二次流逐渐形成并不断增强，最大流速逐渐向凹岸转移，此时横向剪切逐渐增强，横向离散系数逐渐增大；而纵向剪切趋于平缓，纵向离散系数逐渐减小。在弯顶附近，二次流得到充分发展，横向离散系数达到最大值。在弯道下游段，二次流强度逐渐减弱，横向剪切流速减小，使得横向离散系数逐渐减小，此时最大流速转移到凹岸附近，流速分布变化趋于平缓，纵向剪切流速变化幅度较小，纵向离散系数基本趋于稳定。

英文摘要：

Flow structures and dispersion characteristics in a 180°; curved open channel were studied . The 3D Doppler ultrasound anemometer was used to measure the flow velocities on 5 typical cross-sec-tions .Then ,based on the measured velocity data ,the modified N-zone model was adopted to investi-gate the transverse and longitudinal dispersion coefficients .At the entrance of the curved reach ,outer bank velocities are smaller than the inner ones ,resulting in a large longitudinal shear velocity ,and longitudinal dispersion coefficient is relatively higher .As the secondary flow has not been formed yet and lateral shear velocity is not fierce enough ,transverse dispersion coefficient is relatively lower . When heading into the curved reach ,secondary flow is gradually formed and enhanced ,and the maxi-mum velocities begin to transfer to the outer bank gradually .T ransverse dispersion coefficient is grad-ually increased due to the increasing transverse shear effect ,w hile longitudinal dispersion coefficient is rapidly decreased because of the decreasing longitudinal shear velocities .Secondary flow is fully devel-oped near the bend apex w here the transverse dispersion coefficient reached maximum .In the dow n-stream of the curved reach ,the secondary flow begins to decrease and lateral shear velocities become much smaller ,and as a result ,the transverse dispersion coefficient decreased .Longitudinal dispersion coefficient almost achieves stability since longitudinal shear has become much smaller in this region .