Author(s): Weidong Guo; Liping Yang; Yahui Feng
Linked Author(s): Weidong Guo
Keywords: Reynolds stress model; Junction; Separate zones; Numerical simulation; “Y” shaped open-channel junctions
Abstract: In the natural rivers, main channel and tributary confluences exist universally. The confluent reach is a key point to be considered for such projects as water conservation, navigation, flood prevention and environmental protection at all times. The hydraulic characteristics of confluent reach are frequently studied either in the form of gullet model experiments or through prototype observations, but because of nearby junctions, the influence factors such as river channel partial shape and water coming condition of the main channel and tributary, cause its hydraulic phenomenon extremely complex. Physical model experiment is restrained by time and space, making it difficult to obtain synchronizing information of the flow field and sufficient data for explicit analysis of confluent region. This paper explores “Y” shaped open-channel junctions using two-dimensional numerical model. In consideration of the flow characteristics of open-channel junction, the depth-velocity Navier-Stokes equation was closed by anisotropic Reynolds stress model. The finite volume method on staggered grids was used to discrete the equations with the result that the depth-velocity was solved through SIMPLE arithmetic. The validity of the model is verified with relevant experimental data which are in conformity with the arithmetic results. By Reynolds stress model, more hydraulic behaviors of the “Y” shaped junction are revealed including surface configuration、velocity distribution、stress distribution and the complex hydraulic characteristics of separate zones. Nearby the upstream junction corner exist flow stagnation zone. With the discharge ratio decreasing, input momentum from main channel hold dominant, flow stagnation zone skew gradually to tributary side. At the junction, the streamlines bend, causing flow away from the bank and creating flow separation zone at downstream main channel side and downstream tributary side. Flow separation at main channel side is more obvious. Outside the separation zone, flow velocity obviously increases, forming the maximum velocity zone. Separating zone size decrease with discharge ratio increasing. The flow reversal phenomenon is obvious in separation zone. The simulation results indicate that water level is obviously lower in separation region; upstream section water level at junction rises and the stagnation zone at upstream corner achieves topmost level. The drop in longitudinal water surface intensifies along with the increase in discharge ratio. Reynolds stress puts up obvious aeolotropy. Reynolds stress is very large in the separation zone and the stagnation zone, and turbulent mixing in x and y direction is very strong in both zones, especially the separating zone on the side of main channel gets strongest mixing.
Year: 2007