Abstract

The experiments on the 3D movement of bed load particles in open-channel steady flow were performed by a Particle Tracking Velocimetry system. The trajectories of coarse particles with specific density 1.54 and mean diameter 1.90mm were recorded in 5 kinds of steady flow with different slopes. Consequently, the 3D velocity components of particles were calculated, and a statistical analysis of large amounts of particles was carried out. The results showed that the average longitudinal velocity of bed load versus particle Renolds number conformed to an exponential curve, while the mean velocities in the vertical and transverse directions were so low that the particles could be considered to have no significant motion tendency in the two directions. The longitudinal turbulence intensity and turbulence energy turned larger with the increase in Shields number. The mean values of longitudinal and vertical turbulence intensities of particle were about half of those in clear water flow because of the restraints of particle’s diameter and specific density. The probability density distribution of longitudinal velocity approached the normal distribution, except that the peak leaned to the negative direction, and the skewness coefficient increased with the increase in slope. The shape of probability density distribution of vertical velocity was thinner than the normal distribution, while the skewness coefficient tended to be zero. The probability density distribution of the transverse velocity was almost the same with the normal distribution.

Keywords: Shields number, bed load, 3D movement