Experimental research on the flocculation characteristics of cohesive sediment in turbulent flow

The flocculation characteristics of cohesive fine sediment under different conditions of turbulence shear are investigated.The conclusions are as follow.(1) Under a given shear rate,long time evolution of flocculation approaches a state of equilibrium that the statistical mean of the flocs size is steady.(2) Under low shear rate(G 30 or 41s-1) the mean size increases with shear rate as a result of the domination of aggregation over breakup,while under higher shear rate(G 30 or 41s-1) the mean size decreases with shear rate.At intermediate shear rate(G = 30 or 41s-1),the mean size and the flocculation rate are maximized.(3) Under the same turbulence shear condition,the mean flocs size increases with the initial sediment concentration.(4) Evolution of flocculation could be improved by increasing the cation of electrolyte or concentration of electrolyte.(5) The formed flocs stay inside the eddies of size in the same order as Kolmogorov scale,and the maximum floc size decreases with turbulence intensity.The flow around these flocs is laminar,which may cause a surface erosion of the aggregates.