The Numerical Simulation Of Flow Characteristics On Compound Channel

Most natural rivers have flood plains that extend laterally away from the main river channel at a gradient or in a series of terraces. During flood, flows rise above the bankfull stage and inundate the adjacent flood plain areas. The large lateral exchange of momentum takes place in the shear layer that forms between the generally faster moving flow in the main channel and the slower moving flow on the floodplain. The current velocity increases on the floodplain, decreasing in the part of the main channel and also in the whole cross section, which results in the longer time for the flood conveyance. Since flood alleviation schemes are the focus of much engineering work, the prediction of the hydraulic characteristics in such channels is clearly important for engineering design, the transverse transfer of pollutants, sediment transport, the existence of hydrobios, the utilization of river beaches and so on.The Reynolds stress equation model (RSM) is adopted to study the hydraulic characteristics of the channels with different cross-section shapes. The main contents of this paper are as follows:(1) The distributions of main velocity, bed shear stress, turbulent kinetic energy and the turbulence-driven secondary currents are simulated for the rectangular, trapezoidal and compound channel. All the results are compared with those of the original data. It is shown that the simulation of RSM agrees with the experimental results better.(2) The VOF model is adopted to simulate the depression of the maximum velocity below the free surface for the narrow channels.(3) The influence of the side-slope of main channel, water depth of the floodplain and the aspect ratio on velocity distribution, secondary currents and boundary shear stress distribution by are discussed. The results can be used for reference to the engineering design, the theoretical analysis and the macros-decision.