中文摘要：

分汊河道在自然界广泛存在,汊道水流结构复杂多变,分汊口处常常存在水流分离区,分离区内易引起污染物滞留、泥沙沉降等,对污染物输移扩散以及泥沙输移造成很大影响,然而目前有关分汊口分离区的研究非常零星,汊道分离区的尺度特征与变化规律尚不清楚。本文着重研究了不同支汊宽度比及不同入流流量对分汊口水流分离区特征尺寸的影响,针对分汊河道复杂的三维水流结构运动特点,建立了基于非结构网格的三维Reynolds应力精细数学模型,模型计算结果与室内试验实测数据吻合良好,成功地复演了分汊河道中不同断面的流速分布特征与环流结构。进而利用该模型进行数值试验,对不同支汊宽度比和不同来流条件下汊道中分离区的尺寸变化规律进行探讨,提出了计算分离区特征尺寸的经验公式,研究成果进一步加深了对分汊河道水流运动规律的认识,为分汊河道中的水污染防治、河道治理等工作打下一定的基础。

英文摘要：

In braided rivers existing widely in the nature, flow structure is complicated and variable, and separation zones often appear in the bifurcation section. The separation zones, where pollutants are accumulated and sediments are easily deposited, has great influences on pollutants and sediment transport in the rivers. At present, however, the studies on the separation zones of braided river are rare and their characteristic scale and hydraulic features are unclear yet. This paper focuses on the influence of different branch width ratios and flowrates on the characteristic dimension of separation zone. We developed a three- dimensional Reynolds stress mathematical model on unstructured grids for simulation of flow structures in braided river. This model successfully produced the velocity distributions and secondary circulation structures in different flow conditions, and its calculations agreed well with experimental data. Numerical experiments were made to study the variations of separation zones with different branch width ratios and flowrates. An empirical equation was derived for calculation of the characteristic dimension. This work sheds light on the understanding of braided river flow and would provide a basis for pollution control and river regulation.