The 3-D Numerical Simulation Of Flow Characteristics In Channel Regulation River Reach

Spur dike is a kind of hydraulic structure that is widely used in channel regulation engineering for controlling the shape of the nature river. Some complex flow characteristics such as separation, circumfluence appears around spur dikes. It is of great importance for the design of channel regulation structure to explore the effect of spur dikes on flow, and to study the flow structure near the spur dike. Through flume experiment and numerical simulation, preliminary work on computation of water surface profile in regulation river reach, numerical simulation of flow with single spur dike in flume, and 3-D numerical solution of flow around spur dikes group are carried out in this paper.The flume experiment with single spur dike is carried out. Water surface profile and velocity field of flow in flume are measured by manometer tube and propeller current meter respectively. Variations of water surface along longitudinal and horizontal direction are analyzed. The experiment data shows that the region with large surface gradients in longitudinal and horizontal direction locates at the vicinity of spur dike. Backwater appear upstream the spur dike, and there exist a recirculation area at the same side downstream the spur dike.Based on the cross-sectional velocity distribution of flow in natural river, computation expression for correction coefficient of kinetic energy is derived. Actually correction coefficient of kinetic energy reflects the non-uniform characteristics of cross-sectional velocity in natural rivers. It is related with hydraulic parameters and can be expressed by Chezy's coefficient. The larger the resistance of boundary, the more non-uniform the distribution of cross-sectional velocity. Thevalue of correction coefficient of kinetic energy increases as a result.The water surface profiles of flume experiments are computed by three different methods: adjusting the local head loss coefficient, deduction of backwater area, and application of backwater expression. Comparison of water level between measured and computation shows that the local head loss coefficient cannot give head loss by spur dike completely, and the effective area of passage is difficult to be ascertain. For this reason the two methods for water surface profile computation cannot predict the raise of water level upstream the spur dike accurately. Only the method for using backwater expression can predict the variation of water surface near the spur dike very well.Numerical simulations of the flume experiment cases are carried out with the standard k-e turbulence model. Comparison between the numerical results and the measured data shows that it is adequate for the standard k ~ e turbulence model to simulate the complicated flow pattern with the existence of separation and circulation zones. Flow structure near the spur dike is very complicated, and areas with apparent three-dimensional characteristic exist in the vicinity of spur dike.The standard k-e model is adopted to simulate the flow of practical channel regulation projects. The numerical results show that the velocity distribution of flow in the regulation project river reach are mainly controlled by the geometries of natural river. But in local region it is mainly controlled by the regulating structures. The planar velocity is of the parabola distribution. The velocity value in the middle of the river is larger than that of the two banks. The effects of spur dikes group to the flow are different to that of single spur dike. The first one among spur dikes group in regulation river reach has the most important holdback effect than the others. Velocities in regions between upstream and downstream spur dikes are very small, and are often less than the sediment deposit velocity. Silt will deposit there. Velocities around groin head are larger than the scour velocity and scour hole may develop in this area. This would affect the stability of spur dikes.