粘土悬浮液明渠流的减阻现象

THE PHENOMENON OF DRAG REDUCTION IN FLOWS OF CLAY SUSPENSIONS

水和粘土悬浮液在水槽中的流动试验证明，在粗糙边界上的粘土悬浮液明渠流阻力明显小于清水流．在同样水力条件下粘土悬液的时均流速比清水流速大得多．当悬液浓度较高时，流动阻力系数比清水流阻力系数的一半还小．实验表明粘土悬液的高粘性和屈服应力抑制了紊动的发展，减小了紊动剪力，导致阻力降低．对于光滑边界湍流，粘土悬液的阻力系数与清水流的相近。

Experiments with clay suspensions flowing over smooth, gravel and stone beds prove that resistance of the flow may be considerably reduced by the suspended sediment if the flow boundary is rough The measured mean velocity of clay suspensions is much higher than the flow of water The friction factor of flows of high clay concentrations over the gravel bed was less than half of the clear water flow on the same hydraulic conditions The high viscosity and yield stress of clay suspensions suppressed the development of turbulent eddies and thus reduced the turbulence intensity The effect of damping turbulence is the cause of the drag reduction For flows over the smooth bed, the effect of damping turbulence is counterbalanced by the effect of increasing viscous resistance, therefore, no drag reduction occurred in this case