基于耗散粒子动力学的剪切流中黏性沙絮凝机理研究

Study on mechanism of cohesive sediment flocs in turbulence based on dissipative particles dynamics

基于介观尺度下的耗散粒子动力学方法,建立了包含力场势函数的均匀各向同性紊流模型,对不同剪切率条件下黏性泥沙的絮凝过程及絮团形态进行了模拟计算。结果表明:随着剪切率的增大,体系中絮团初始出现的时间先急剧减小,后经短暂平稳过渡,又迅速增大,最后基本保持不变;水体剪切率较小时,非键能减小速度较快,随着剪切率进一步增大,非键能减小速度逐渐变缓,体系稳定性逐渐降低;当剪切率较小时,絮团形态更为致密,分形维数逐渐增大;随着剪切率的进一步增大,伴随有多个小絮团出现,分形维数逐渐减小,最终保持在1.12左右;在紊动剪切条件下,体系中絮团一直处于碰撞、絮凝、破碎的动态过程。

Based on the dissipative particle dynamics method at mesoscale scale,a uniform isotropic turbulence model with force field potential function is established and the process of cohesive sediment flocculation and flocs morphology under different shear rate conditions are simulated.Results show that the appear time of flocculation decreases sharply at first with the increase of shear rate,then smooth and steady transition and then increases rapidly,and finally remains unchanged.When the shear rate is small,the non-bond energy decreases faster.As the shear rate increases further,the non-bond energy decreases gradually and the stability of the system gradually decreases.When shear rate is small,the number of final flocs decreases with the increase of shear rate,the morphology of flocs are more dense,and the fractal dimension increases gradually.With the further increase of shear rate,the number of flocs increased,accompanied by the appearance of multiple small flocs,the fractal dimension gradually decreased,and finally remained at about 1.12.The flocs have dynamic processes of collision,flocculation and crush in a shear condition.