Non-equilibrium flocculation characteristics of fine-grained sediments in grid-generated turbulent flow
Non-equilibrium flocculation characteristics of fine-grained sediments in grid-generated turbulent flow
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DOI：
10.1016/j.coastaleng.2009.11.011
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发表时间：
2010-04
影响因子：
4.4
通讯作者：
A. Cuthbertson;P. Dong;P. Davies
中科院分区：
文献类型：
--
作者：
A. Cuthbertson;P. Dong;P. Davies
结果来自一系列沉降柱实验，研究纯粘性（高岭土）沉积物悬浮液以及粘性（高岭土）和非粘性（细砂）沉积物混合物的絮凝特性的时间变化。实验运行是在由同相振荡网格的刚性阵列产生的受控流体动力学条件下进行的。结果表明，在低湍流剪切速率下发生快速的初始絮凝体聚集，在相对较短的时间段内达到峰值最大和均方根（r.m.s.）絮凝体尺寸（分别为~400μm和~200μm），然后随着时间的推移而减小。相比之下，在较高剪切条件下观察到较低的聚集率和较小的絮凝体尺寸，由于湍流增加，絮凝体在沉降塔中悬浮的时间更长。泥浆输入浓度与最大和均方根值显示出一定的相关性。在较高剪切速率下絮凝体尺寸但在低剪切速率下没有明显相关性。这种观察到的絮凝物行为可能归因于高剪切速率和低剪切速率下浓度梯度的差异，该差异影响絮凝物沉降速率和絮凝物达到平衡尺寸所需的时间。向高岭土悬浮液中添加细砂部分降低了初始絮凝体形成（即聚集）速率以及最大和均方根值。整个实验中获得的絮凝体尺寸。混合物中细砂与高岭土含量之比的增加似乎增强了最大絮凝体尺寸的减小。
Results are presented from a series of settling column experiments investigating temporal variations in the flocculation characteristics of purely cohesive (kaolin clay) sediment suspensions and cohesive (kaolin) and non-cohesive (fine sand) sediment fraction mixtures. Experimental runs were conducted under controlled hydrodynamic conditions generated by a rigid array of in-phase oscillating grids. The results indicated that rapid initial floc aggregation occurred under low turbulent shear rates, with peak maximal and root-mean-square (r.m.s.) floc sizes (∼400μm and ∼200μm, respectively) attained after relatively short time periods, before reducing with time. By contrast, lower aggregation rates and smaller floc sizes were observed under higher shear conditions, with flocs retaining suspended in the settling column for longer time scales due to the increased turbulence. The mud input concentration displayed some correlation with maximal and r.m.s. floc sizes at higher shear rates but no correlation was apparent at low shear rates. This observed floc behaviour may be attributed to the differences in concentration gradients at high and low shear rates that affect both floc settling rate and time required for flocs to attain equilibrium size. The addition of the fine sand fraction to the kaolin clay suspension reduced both the initial floc formation (i.e. aggregation) rate and the maximal and r.m.s. floc sizes attained throughout the experiments. The reduction in maximal floc sizes appeared to be enhanced by an increase in the ratio of fine sand to kaolin clay content within the mixture.