基于雅鲁藏布江辫状河流的洪峰流量输沙变异数值模拟

Numerical Simulation of Sediment Transport and Variation Based on the Braided River of Yalu Tsangpo River

根据雅鲁藏布江中游辫状河流平面形态建立输沙地形,构建了可用于辫状河流输沙模拟的数学模型。采用2维水动力学和非黏性泥沙耦合模型,对辫状河流中泥沙输运规律进行数值模拟研究,模型基于不可压缩雷诺平均N-S方程,包括连续方程、动量方程、河床面变形方程、全沙输沙方程。模型通过全沙输移理论计算悬移质和推移质输沙率。结果表明:当模拟洪峰流量时,辫状河流出口含沙过程和悬移质输沙过程峰值滞后于入流过程,形成相位差,泥沙粒径越小,相位差越小,中值粒径为0.01和0.02 mm泥沙相位差接近0,出口悬移质输沙率产生的相位差小于含沙量;中值粒径为0.30、0.20和0.10 mm泥沙在辫状河流中的淤积量超过50%。在计算泥沙输移的同时,考虑泥沙的启动、沉降淤积作用导致的地形更新,进而求解挟沙水流在辫状河流中运动时对地形变化的影响,为天然辫状河流的研究预测建立一定的数值模拟基础。

Based on the shape of the braided river in the middle reaches of the Yalu Tsangpo River,the study established a mathematical model for the simulation of sediment transport in braided rivers.The numerical calculation used a two-dimensional hydrodynamic and non-viscous sediment coupling model to simulate the sediment transport in the braided river.The model is based on the incompressible Reynolds average N-S equation,which included continuous equations,momentum equations,riverbed deformation equations,and total sand transport equations.The mathematical model calculated the suspended sediment and the sediment transport rate through the theory of total sediment transport.When simulating flood peak flow,the peak of the sediment concentration process and the suspended sediment transport rate of the braided river lags was behind the inflow process,causing a phase difference.The smaller the sediment particle,the smaller the phase difference.The phase difference of sands,whose particle sizes were 0.01 mm and 0.02 mm,was about 0,and the phase difference caused by the rate of exit suspension sediment transport was less than that caused by sediment concentration.The sedimentation of 0.30 mm,0.20 mm and 0.10 mm particle size in the braided river exceeded 50%.In the calculation of sediment transport,the topographic renewal caused by sediment start-up and sedimentation was considered,and the influence of the sediment flow on the topographic changes during the movement of the braided river was analyzed,which established a numerical simulation example for the research prediction of the natural braided river.