A numerical study of the flow structure in a gravel river bed

The flow structure on rough bed is a fundamental issue of sediment research. The relationship between the flow structure and the bed form in gravel river bed is generally close and complex. Concerning the microstructures in bed-form, the nearbed flow structure, which plays an important role in bed load transport, becomes more complicated. In this paper, a numerical study was presented over a fixed gravel bed by using RSM (Reynolds Stress Model) turbulent models in staggered grid. The specific objectives of the study are: (1) obtaining the velocity and Reynolds stress profile on the rough bed; (2) determining the variation of turbulence parameters (Reynolds stress) along the flow depth; (3) obtaining detailed turbulence parameters. The simulation results have been validated with the corresponding experimental data. The results are coincident with the measured values to some extents, which reveal that the flow structure near the bed tends to be three-dimensional; the velocity profile no longer fits with the logarithmic law in near wall region, and the turbulence intensity increases in the near wall region as the presence of particles protrusion. With the detailed data of numerical simulation, it can help to further understand the interaction mechanism between the flow structure and the bedform. © 2008 Civil-Comp Press.