双峰型非均匀沙粗细颗粒相互作用对推移质输移的影响

为研究粗细颗粒间相互作用对非均匀沙输移的影响,采用推移质动态采集、图像识别和多普勒测速技术,实现了瞬时输沙量、颗粒组成与近壁脉动流速的实时同步监测。针对双峰型非均匀沙进行了211组推移质系列水槽试验,分析表明:推移质输移量与粗沙拣选度的随机波动与紊动猝发引起的流速脉动具有响应关系;推移质中细粒基本保持持续输移,而粗粒输移则具阵发性,并遵循促发、触发与失怙3种模式;颗粒组成结构对3种模式的实施过程有重要影响;它制约着泥沙中细粒对粗粒的激励、碰撞和解怙强度,使得推移质总沙、细沙和粗沙输移率随床沙组成的改变各自呈现出不同的变化规律;水流强度一定时,随床沙粗细比的减小,输沙率呈驼峰型曲线变化;只有适宜的粗细颗粒搭配(ηc)才能使非均匀推移质输沙率达到峰值,且大于该床沙组成中任一均匀沙的输沙率。

Interactions between the coarse and fine particles and their influences on the bimodalnon-uniformbed load transport

In order to study the impacts of the interactions between the coarse and fine particles on the non-uniform sediment transport, the real time simultaneous monitoring of the sediment delivery amount, grain composition and the fluctuating velocity near bed have been realized,based on the technologies of instantaneous bed load acquisition, image identification and Doppler velocity measurement, etc. Aimed at the non-uniform sediment with bimodal pattern, 211 cases experiments on bed load transport have been carried out under series flume conditions. The analysis indicates that the random fluctuation of the bed load transport quantity and selection degree of the coarse particles have some response relations with the velocity fluctuation caused by the turbulence burst near the bed. The fine particles in the bed load mostly remain continuously transport in a process, however, the transport of the coarse particles is always paroxysmal, abiding by three modes:priming,triggering and breaking. The structure of particles composition plays an important role in the enforcement of the three models. It restricts the effect intensity of exciting, colliding and breaking of the fine particles on the coarse particles, which results that the transport rates of the total, fine and coarse show different variation trends respectively with the changing of the bed material composition. At a certain flow intensity, the transport rate presents a hump curve with the decrease of the thickness ratio of bed load. Only if the ratio is appropriate,may the transport rate of the non-uniform bed load reach the peak, which is higher than either transport rates of the uniform coarse or fine sediment in this non-uniform sediment. Such cognition may give a significance reference for the improvement of non-uniform sediment transport theory.