紊动对黏性泥沙絮凝沉降影响的实验研究

Experimental Investigation of the Influence of Turbulence on the Flocculation and Settling of Cohesive Sediment

在圆柱形沉降筒中利用多层格栅产生近似各向同性紊流场,研究盐水和淡水中紊动对黏性泥沙絮凝沉降的影响,分析絮团粒径、体积含量和泥沙浓度变化.研究结果表明:在相同剪切率条件下,和在淡水中相比,盐水中黏性泥沙絮凝时间缩短,絮团粒径增加,然而盐度对絮团体积含量影响并不明显;最大絮团粒径随着紊动剪切率的增加先增大后减少,最大絮团粒径对应的紊动剪切率在盐水中为20.8,s-1,淡水中为15.6,s-1;随着紊动剪切率的增加,水体中泥沙平衡浓度增大,达到平衡所需要的时间缩短.

An array of oscillating grids was applied in the cylindrical settling column to generate quasi-isotropic tur-bulence flow. The experiments were carried out to clarify the influences of turbulence on cohesive sediment floccula-tion and settling in salt water and fresh water. The floc size distribution,volume fraction and suspended sediment concentration were analyzed based on the experimental results. The results show that the flocculation time is shorter and the floc size is larger in salt water than those in fresh water. However,the effect of salinity on the floc volume fraction is not obvious under the same shear rate conditions. The maximum floc size firstly increases,then decreases with increasing shear rate. When the maximum floc size is formed,the shear rates are 20.8s-1 and 15.6s-1 in salt wa-ter and fresh water,respectively. Furthermore,with the increase of the shear rate,the sediment equilibrium concen-tration increases and the time required for equilibrium decreases.