二次流对微弯河段水沙输移影响的数值模拟研究

Modeling effects of secondary flow on transport of flow and sediment in a slightly curved reach

二次流运动是影响弯道内流速、含沙量分布及河床冲淤变形的重要因素。以往二维数学模型很少考虑二次流运动对水沙输移的影响。本文采用Delft3D模型的二维计算模块,通过在水沙输移方程中添加附加应力项来考虑二次流运动的影响,计算了不同流量级时荆江沙市微弯河段的水沙要素分布,并用实测流速和含沙量资料验证了模型的可靠性。在此基础上,详细分析了二次流运动对流速、含沙量分布的影响,以及上游来流量大小与二次流对水沙输移影响程度的关系。最后对水流运动方程中的二次流附加应力项、水面比降项及阻力项的大小进行了量级分析。这些计算结果表明:二次流对水沙输移的影响程度随着来流量的增加而增大,但在微弯河段其影响程度很小。

The secondary flow is an important factor that affects the distributions of velocity and sediment, and morphological evolution in meandering reaches. However, previous two-dimensional （2D） mathematical mod- els can not account for the effect. In this study, the 2D calculation module of the Delft3D software is used to simulate the distributions of flow and sediment factors under different incoming discharges in the Shashi reach with a slight curvature in the Upper Jingjiang River, because it can account for the effect of secondary flow through the introduction of additional stress terms in the governing equations. The model＇s capacity is validated using the measured data of flow velocity and sediment concentration in this reach. The effects of secondary flow on the distributions of flow and sediment factors are then investigated in detail, as well as the relationship between the magnitude of incoming discharge and the influencing degree of secondary flow on the transport of flow and sediment. Order analysis for the specified terms in the flow governing equations are conducted using the model results, including the additional stress for secondary flow, water surface slope, and bed roughness, which indicate that the influencing degree of secondary flow on the transport of flow and sediment would enhance with the increase of incoming discharge, but the effect could be neglectable in a slightly curved reach.