Rheological Characteristics and Dynamical Mechanism in Hyperconcentrated Sediment-laden Flow

在黄河流域，了解和预测携带大量悬浮泥沙的水流的需求已经变得非常迫切。在黄河流域，与高浓度泥沙洪水相关的严重侵蚀和淤积导致了许多严重的河流问题。泥浆流、泥石流或泥浆，由悬浮在水中的大量粘土和/或淤泥颗粒组成，通常表现出非牛顿性质，但对其流变性能的了解仍然很少。本文首先对黄河下游地区沉积的高岭土颗粒或粉砂颗粒进行了充分发育的紊流管流实验研究。流动数据包括摩擦系数与雷诺数、体积泥沙浓度、平均流速。此外，采用同轴圆柱形流变仪和平行平板流变仪对泥石流流变特性进行了研究。试验结果表明，在低剪切速率下，高含沙量时，由于黏度的增加，泥浆的摩擦系数随含沙量的增加而增加2 ~ 3个数量级。此外，利用粒子图像测速技术（PIV）研究了非牛顿流体对固定沙丘床分离涡的影响。结果表明，与清水流动相比，沙丘床的流变性能显著地消散沙丘床上的湍流波动，增大沙丘床上的流动阻力。最后，利用颗粒图像测速技术（PIV）研究了非牛顿流体对砾石床层阻力特性和流动结构的影响。结果表明：在砾石层明渠流中，高岭土水混合物对水流结构有明显的改变，在Cv <8%范围内，高岭土水混合物的阻力减小，在Cv <8%范围内，高岭土水混合物的阻力增大；少

The need to understand and predict flows that carry large suspended sediment loads has become acute in the Yellow River basin where significant erosion and siltation associated with hyperconcentrated sediment-laden flood give rise to many serious river problems. Mud flows, debris flows or slurries, made up of a large amount of clay and/or silt particles suspended in water, often show non-Newtonian properties but remain poorly understood concerning their rheological properties.First of all, this paper concerns an experimental study of the fully developed turbulent pipe flow with kaolin particles or silt particles deposited in lower region of the Yellow River Basin. The flow data include friction factor vs. Reynolds number, volumetric sediment concentration, mean flow velocity. In addition, the rheological properties of the mudflows were investigated by using both coaxial cylinder rheometer and parallel plate one. The experimental results stressed that at high sediment concentration mudf … More lows did not fit to the Bingham model at low shear rates, the friction factor increased with the sediment concentration which result from the viscosity increase by two to three orders magnitude.In addition, we experimentally investigated the effects of non-Newtonian fluid on the separation vortex over fixed dune type bed by using Particle Image Velocimetry(PIV). The results showed that rheological properties significantly dissipated the turbulent flow fluctuations over the dune bed and augmented the flow resistance by comparison with the clear water flow.Finally, we experimentally investigated the effects of non-Newtonian fluid on resistance characteristics and flow structure over gravel bed by using Particle Image Velocimetry (PIV). The results showed that Kaolin water mixtures in gravel bed open channel flows considerably changed flow structures and took the form of resistance decrease with Kaolin fraction Cv in the region of Cv <8% and followed by a subsequent increase in the region of Cv >8%. Less