Experimental study on the effect of hydrodynamic conditions on flocculation and settling properties of fine-grain sediment  

作　　者：Bismark Odum Chunyang Xu Yongping Chen Yinpeng Yao Yan Zhou 

机构地区：[1]The National Key Laboratory of Water Disaster Prevention,Hohai University,Nanjing 210024,China [2]College of Harbor Coastal and Offshore Engineering,Hohai University,Nanjing 210024,China [3]School of Engineering,University of Liverpool,Liverpool L693BX,UK

出　　处：《International Journal of Sediment Research》2023年第6期821-833,共13页国际泥沙研究（英文版）

基　　金：This research was supported by the National Natural Science Foundation of China(Grant Nos.51979076 and 52211530103);the Fundamental Research Funds for the Central Universities(Grant No.B230201047);the National Natural Science Foundation of China(Grant No.51709084).

摘　　要：The flocculation of cohesive sediment particles is a function of the collision efficiency of sediment particles,which is mainly influenced by local flow hydrodynamics.A detailed study on local hydrodynamic characteristics in a novel stirred tank was done to measure the flow field of a turbulent flow.Instantaneous flow velocity fields were obtained and processed,and the average flow field was computed.Particle image velocimetry(PIV)results measuring the hydrodynamic characteristics(expressed as turbulent kinetic energy(TKE),local dissipation rate of TKE,velocity gradient or shear rate,turbulent shear stress,etc.)were analyzed and discussed.Particle tracking and automated image processing techniques were utilized to analyze the impact of the hydrodynamic conditions on the floc and settling properties.The differences in floc properties under the two turbulent shear states(i.e.,steady-state(SS)and unsteady-state(US))hydrodynamic conditions were examined.The results show that floc size and floc size distribution(FSD)of pure kaolin clay flocs are significantly influenced by the local dissipation rate of TKE and the turbulent intensity states.The floc size,df,84,at local dissipation rate of TKE of 11×10^(-4),29×10^(-4),44×10^(-4),83×10^(-4),and 142×10^(-4)m^(2)/s^(3)is 97,108,107,124,and 150 mm,respectively.It was found that by increasing the local dissipation rate of TKE,the FSD was skewed left.The US shear condition generated larger flocs(and in higher proportions)relative to the SS condition.The settling velocity and flux settling velocities of flocs formed under SS conditions are higher than those formed under US conditions.The fractal dimension of SS flocs also is higher than the fractal dimension of US flocs.These results highlight a significant impact of the states of hydrodynamics on floc properties such as floc size and FSD as well as the settling and morphological properties of flocs.

关 键 词：Turbulent kinetic energy Turbulent shear rate FLOCCULATION Floc size Settling velocity 

分 类 号：TV145[水利工程—水力学及河流动力学]