分汊型明渠非均匀沙输移机理研究

Sediment transport of braided channel is ubiquitous in alluvial rivers, which is characterized by typical multi-compositions, multi-processes and multi-scales,. The mobile bed boundary of the braided channel exist difference in the longitude and the transverse directions and strong turbulent dissipation effect as well as flow-sediment mixing and distribution process are common in bifurcation and confluence areas, which makes sediment transport by turbulent flow has its particularity. In addition, the unsteady incoming flow and sediment as well as the nonuniform compositions of channel bed render this problem more complex. In this project, the mechanism of sediment transport under unsteady flows and nonuniform bed materials will be investigated and the coupled depth-averaged numerical model will be established. The scientific goal is to reveal the features of non-uniform sediment transport in the braided channels, especially the distribution, adaptation and mixing process of sediments in the flow and over the channel bed in bifurcations and confluences. The response mechanism of sediment transport to different flow and sediment conditions will be investigated.

分汊型明渠输沙过程是一类典型的多组分、多过程与多尺度的流动过程。分汊型渠道底部床面边界存在纵向和横向的差异，且在分汇流区存在较强的湍流扩散作用和水沙分配与混合过程；同时，边界来水来沙和底部可动边界的非定常性及床面泥沙组成的非均匀性使对这一问题的研究更趋复杂。本课题旨在研究分汊型渠道在非定常流动和非均匀沙床面组成条件下的泥沙输移机制及其耦合积分模式理论，其科学目标是：揭示大尺度条件下分汊型渠道水沙输移规律，特别是分汇流区泥沙分配与混合规律及床面泥沙的时空调整规律；研究分汊型水沙输移对不同床沙组分和边界水沙条件非定常性的响应机理。

分汊型渠道广泛存在于自然界之中，其演变过程与工程实际问题息息相关。明渠输沙是分汊型渠道演变的重要过程之一，也是一类典型的多组分、多过程与多尺度的流动过程。本课题充分考虑分汊型渠道在非定常流动和非均匀沙床面组成条件下的泥沙输移特点，通过对非均匀沙进行级配分组、采用床沙活动层计算模式描述床沙级配变化过程，在此基础上，基于流体力学守恒律和深度积分近似假定，推导出了更完善的水沙基本控制方程组；同时，采用了基于中心变量存储方法，应用Godunov型高精度数值计算方法建立了平面二维非结构三角型-四边形混合网格有限体积水沙耦合数值模型。通过经典算例和室内水槽实验讨论了模型的特征，印证了模型的可靠性、稳定性和精度。通过长江上游典型分汊型河道的数值模拟研究，结合水槽试验分析，探究了分汊型渠道水沙输移及渠道冲淤变化规律。