RESISTANCE AND DRAG REDUCTION OF FLOWS OF CLAY SUSPENSIONS

Drag reduction in flows with clay mineral particles was experimentally studied, Experiments with clay suspensions flowing over smooth gravel , and stone beds proved that resistance of the flow may be considerabl y reduced if the flow boundary is rough. The friction factor of hows o f high clay concentrations over the gravel bed was less than half of t he clear-water flow at the same discharge and energy slope. At low con centrations, a flee of clay particles having a long-chain structure ma y damp turbulence and result in drag reduction. At high concentrations , all flocs in clay suspension connect together and form a three-dimen sional net structure, which affects the resistance in two ways: (1) By damping turbulence; (2) by increasing the viscous resistance. For flo ws over rough boundaries, turbulent shear dominates the resistance and high clay concentrations cause drag reduction. For flows over a smoot h bed, the effect of damping turbulence was counterbalanced by the eff ect of increasing viscous resistance; therefore, no drag reduction occ urred.