紊流对粘性细颗粒泥沙絮凝影响

以分形聚集生长模型为基础,通过三维模拟泥沙颗粒在布朗运动、重力沉降和紊流作用下的碰撞、粘结和破碎过程,探讨了紊流对粘性细颗粒泥沙絮凝速度、絮团平均粒径及分形维数的时空影响。试验结果表明:紊流作用下,泥沙絮凝及絮团平均粒径的变化可分为加速段、等速段和减速段,絮凝等速段的作用时间及粒径等速增长段的速度均随紊动强度呈先增后减的规律,且中部区域的絮凝速度和絮团平均粒径较小;泥沙絮团分形维数随水流紊动强度的增加逐渐增大,最终趋于稳定,随时间呈先减后增的规律。模拟空间下部区域分形维数最大,上部次之,中部最小。

Effect of turbulent flow on flocculation of fine cohesive sediment

Using the fractal cluster growing model, the effect of turbulent flow on the flocculation velocity, the average diameter and the fractal dimension of flocs are studied. The model simulates the collision, the bonding and breakage of sediment particles under the action of Brown motion, gravity settling and turbulent flow in a three-dimensional space. The results show that the process of flocculation and average diameter of flocs can be divided into three stages: accelerating section, uniform section and descending section. The flocculation duration of uniform section appears to be first increasing then decreasing as the turbulent intensity increased, and so do the growth of average diameter. Moreover, the flocculation velocity and the flocs average diameter are smallest in the central region. The fractal dimension of flocs increases with the turbulent intensity increasing, and is finally stabilized. Besides, the fractal dimension of flocs appears to be first increasing then decreasing with time. The fractal dimension of floc is largest in the lower region, followed by the upper region, and the lowest value is found in the middle region.