瞬时排放泥沙颗粒团在横流中对流扩散特性的实验研究

河道维护、航道开挖及疏浚等一些工程,常常将挖掘的泥沙抛入流动的水体中,利用横流对泥沙颗粒团的对流扩散作用来稀释泥沙浓度.针对这类工程进行水环境质量影响评价时,首先要识别泥沙的运动特性.通过实验手段,研究不同级配的泥沙颗粒团瞬时排放后在横流中迁移扩散混合特性.实验结果表明,泥沙颗粒团进入水体后,在浮力、重力、阻力和横流紊动的综合作用下发生对流扩散;横流是产生泥沙对流运输的主要动力,横流的紊动作用,加强了泥沙颗粒团与水体的混合作用,并且破坏了其在静水中的双漩涡结构,因此大大地增加了垂向前锋位置和纵向扩散宽度.通过分析得出了无量纲泥沙颗粒团垂向前锋位置与时间、纵向扩散宽度与时间以及垂向前锋位置与纵向扩散宽度的3个关系式中的参数(α₁、α₃和α₂)均值及其变化范围,可应用于抛泥对水体环境的影响评价.

Experimental study on dispersion of instantaneous discharging sediment cloud in cross-flow

The artificial instantaneous discharge of dredged sediments in flowing waters is usually subjected to cross-flow action In shallow waters the initial discharge and cross-flow conditions are significant for the deposition pattern.T he determination of the characteristics of this problem is thus important before environmental impact assessment can be made.In the present study,a series of laboratory experiments are carefully conducted to investigate the transport and mixing of an isolated sand cloud in cross-flow.The results show that the sediment cloud is dispersed under the forces of buoyancy,gravity,drag force and turbulence of cross-flow The cross-flow is the main driving source for the advection of sediment cloud.The turbulence of cross-flow increases the mixing of sediment cloud and the ambient flowing water,and destroys the double vortices occurring in the stagnant water Thus the vertical frontal position and longitudinal width increase The analysis of experimental data gives the empirical constants and their variance,which can be used to determine the relationships of non-dimensional vertical frontal position and time,longitudinal width and time,and vert ical frontal position and longitudinal width All these results can be used to assess the environmental impact of dumping projects.