黏性泥沙受紊动剪切作用下的絮凝效果研究

我国水库运行一直面临着泥沙淤积的问题,而水动力条件的改变对泥沙的絮凝有莫大的影响,针对此问题,研发了一套絮凝沉降装置,以三峡库区长寿河段泥沙为样本,利用多层震动格栅在圆柱形沉降筒中产生各向同性均匀紊流,结合絮凝沉降观测装置,研究分析紊动剪切作用对黏性泥沙絮凝的影响,并得出了基于试验的最优剪切率。结果表明:紊动对于泥沙颗粒的絮凝有较明显的促进作用,且随泥沙浓度的增大(0. 3~1. 0 g/L),絮凝程度也相应地增加;紊动剪切对于中、大颗粒絮体(0. 048~0. 384 mm)的分布具有较大影响;泥沙颗粒在进入沉降柱后可以在几十分钟内快速完成絮凝,在30 min左右即可观测到最大颗粒絮体,随后颗粒最大粒径逐渐下降直至平衡;随着紊动剪切率的增加,其对于絮凝的作用呈现先促进后抑制的规律。

Study on flocculation effect of cohesive sediment under turbulent shear action

The reservoir operation in China is confronted with the problem of sedimentation all along，while the change of hydrodynamic condition has great influence on the flocculation of sediment. For this problem，a set of flocculation settlement devices is developed，and then the influence from the turbulent shear action on the flocculation of cohesive sediment is studied and analyzed herein in combination with a flocculation settling observation device with the isotropic homogeneous turbulence that is generated in a cylindrical settling tube with a multi-layer vibration grid by taking the sediment in Changshouhe Ｒiver Ｒeach within the Three Gorges Ｒeservoir Area as the study sample，thus this experiment-based optimal shearing rate is obtained. The result shows that turbulence has a significant promoting effect on flocculation of sediment particles，while the flocculating degree accordingly increases along with the increase of the concentration of sediment (0. 3 ～ 1. 0 g /L) as well，and then turbulent shear has a larger influence on the distribution of the flocs of medium and large particles (0. 048 ～ 0. 384 mm). After entering settling column， sediment particles can quickly complete flocculation within a few tens of minutes，for which the maximum particle of floc can be observed after about 30 min. Whereafter，the maximum particle size gradually decreases until equilibrium. Along with the increase of the turbulent shearing rate，its effect on the flocculation show a law of promoting at first and then restricting.