高含沙“浮泥”运动判别水槽试验

Experiments on critical judgment parameter of heavily silt-laden fluid mud

为研究高含沙"浮泥"及其后续异重流水流要素的变化,以进口流量、含沙量和"浮泥"的含沙量为变量,在水槽中开展了21次异重流与"浮泥"作用概化试验.结果表明,具有宾汉剪切力的"浮泥"与不同含沙量形成异重流的水流剪切力的差别作用,产生了有区别的头部形态,可分为侵入型与界面型;不同含沙量的异重流不仅影响了浑水厚度和掺混情况,而且决定了异重流头部运动形态,异重流的流量主要影响异重流的浑水厚度和运动速度;前期异重流沉降形成的"浮泥"随历时的增加容重增加由快到慢.结合理论分析,获得了"浮泥"层起动的临界判数;基于试验数据,提出了由异重流厚度、比降、体积比含沙量组成的计算公式.研究成果既可丰富河流泥沙动力学学科内容,又可为多沙河流水库调度与规划设计提供技术参考.

In the heavily silt-laden river, density current belongs to an excellent method for flushing the input sediment without water level drawn down. Heavily silt-laden fluid mud in reservoir comes from heavily silt-laden density current. Density current comes into being in the reservoir and may reach the front of the dam with certain flood duration in addition. And the flood also needs to meet a certain sediment concentration and discharge. That makes water and sediment input need to provide density current with energy to overcome the energy loss during the forming process. For example, in a density current creeping process, the current energy shortage often can unsuccessfully reach the front of the Xiaolangdi dam, the stop makes a muddy pond before the dam. Another situation occurs during the density current flushing process. When the input flood ends without subsequent enough energy retention, the foremost density current creeps slowly and suspends before the dam. In these two cases, the muddy layer along the vertical section in front of the reservoir dam will be called fluid mud in this paper. On the basis of understanding the mixing characteristics of hyper-concentrated flow settlement characteristics, viscoelastic and Bingham fluid in the Yellow River, under the flume experiments combined with theoretical analysis method, the formula which concludes high sediment rheological properties of mud and sediment particle size, the volume ratio of sediment concentration, is established and fluid mud layer theoretical analysis had been carried out and flume experiments had been combined to carry out about the effect between density currents and fluid mud. It is found that the difference between the fluid mud with the Bingham shear stress and the flow shear stress due to different sediment concentration, which can divide the movement regime into 2 types, named invasive and interface. The heterogeneous density flow of different sediment does not only affect the muddy water thickness and blending extent, but also determine the movement regime of the head. The flow discharge mainly affects the muddy water thickness and the velocity of the density current. The density of fluid mud increased from fast to slow with the time lasting, which is formed due to settlement. Through the theoretical deduction, the critical judgment parameter of the fluid mud layer incipient motion is obtained. The calculation formula which concluded volumetric sediment concentration, slope and density current thickness is proposed based on the experiments. Obviously, timely opening the desilting tunnel or with the help of the subsequent flood, this will enable the fluid mud incipient motion and flushing out of the reservoir to achieve the purpose of efficient sediment transport. With the adhesion of the fine sediment mud layer in group settlement mechanism and process, conditions on follow-up density current occurrence, and fluid mud layer motion possibility, and its interaction are the basis and key technology of efficient way flushing sediment out of the reservoir in the heavily silt-laden river. The research results can enrich the contents of river sediment dynamics and provide technical reference for the operation and planning of sediment-laden river reservoir.