Author(s): Qingyuan Yang; Tonghuan Liu; Weizhen Lu; Xiekang Wang
Linked Author(s):
Keywords: Free surface; Dynamic meshes; Confluence flow; Rigid-lid; VOF
Abstract: Due to the interaction between branch flow and main stream at confluence zone in open channel, the water level of free surface often varies dramatically. For the three dimensional simulations of confluence flow, multi-phase models are usually adopted in treating the free surface boundary, e. g., the Volume of Fluid (VOF) model. The major dilemmas for adopting multi-phase models are solving multi-governing equations, meanwhile, more refine meshes are needed to cover all regions where water probably cover, and the impact of air on water is often over-predicted. The method of multi-phase modes always consumes more time and computation resources. In this study, the new mesh technique, the dynamic meshes are adopted to track the position of free surface, and so, it will solve less governing equations with fewer meshes near the surface. The results of numerical simulation show that the method of adopting dynamic meshes converges rapidly and produces good agreement with the experimental data. At the beginning, the water level of free surface is assumed flat. During the phases of numerical modeling, the position of free surface is adjusted according to the updated flow field at previous time step. The simulation will keep continuous until the kinematic condition and dynamic condition are both satisfied concurrently. In addition, simulations and comparisons of different turbulence models coupled with dynamic meshes, rigid-lid, or the VOF method are carried out to investigate the impact by tracing the free surface boundary. The simulated position of free surface, velocity distribution and vector field are all compared to the data collected in the flume test. The comparisons show that tracing the free surface is more important than choosing the turbulence models in the simulations of confluence flows. The results of numerical simulations of confluence flow using the dynamic meshes present much better accuracy than that of VOF or rigid-lid method, although they take the same turbulence model.
Year: 2013