固液混相開水路流れの水理特性に関する研究 (2)

Abstract

The effect of suspended sediment on flow resistance has been one of the most interesting andcomplicated problems in fluvial hydraulics. The behavior of sediment-laden flow can not beunderstood in detail without sufficient knowledge of the variation of flow resistance. This paperdeals mainly with the resistance characteristics of free surface shear flows over smooth and/or roughbeds with suspended sand particles, comparing with the clear water flow of the same discharge.Main results obtained through the experimental investigation are as follows; 1) According tothe velocity profile plotted on the semi-log paper, the flow above viscous sublayer is devided intotwo regions; one is the lower region corresponding to so called logarithmic-law region and theother the higher corresponding to the outer region where the velocity profile has steeper slope.2) When sand particles are suspended, the velocity of a flow over smooth bed is decreased especiallynear the bed, while, over rough bed, it is increased especially near the water surface. Therefore, the velocity gradient becomes larger. 3) The friction factor of sediment-laden flow over smoothbed increases with increasing in the sediment concentration, while that over rough bed decreasescontrarily. Such property of friction factor is reconfirmed by the relation between the relativefriction factor and the roughness Reynolds number in a constant sediment concentration. 4) In asediment-laden flow, longitudinal sand streaks associated with low speed streaks are found out nearthe bed. The histogram of sand streaks is approximately described by the log-normal distribution, and the mean value of lateral interval of adjacent streaks is about 1.4 times of the water depth.