Numerical Simulation Of Aeration Flow In Stepped Spillway

Stepped spillway is a facility which is very good at energy dissipation.The author conducted an experiment on stepped spillway based on previous experiments.In this paper,stepped spillway is simulated in three-dimension by using the software named FLOW-3D,Starting from the Navier-Stokes equation and finite volume method,discrete controlling equations were used in the experiment.The mathematical models used were air entrainment model,drift-flux model,viscosity,turbulence model(RNG ?-?)and GMRES algorithm.Multi-block and Favor technology were used for mesh gencration.Flow-3d softwarc was used to simulate the self-aerated and aerartor flow of discharge wall.Our results matched well with previous experiments.According 10 the simulation on three different types of stepped spillways the water level upstream reservoirs are:10cm,15ccm 20cm,25cm,and 28cm.The corresponding flow is 0.0499m2/s,0.118 m2/s,0.187 m2/s,0.269 m2/s,and 0,319 m2/s.The initial aerated position occurs point,the disiribulion of air concentration,flow regime,flow velocity distribution,stepped inside the flow regime,and steppted cross section effect of energy dissipation law are all acquired in the simulation,The result show that when the water flow reaches the crest fhrough the transition section,the surface level will significantly decrease.Once entering the downstream face of dam,the surface level will firstly decrease and then stay stable.With the increase of water depth,thw phenomenon of appearing contration section in initial steps will become less obviou,A large clockwise swirl flow will appear inside the steps.Because of the increased water depth,it will be hard for air to be involved in water and aerated initial position will also come down,At the same level of the section,less changes of air concentration happen at the bottom of the stairs than the upper portion of the stairs.The closer to the surface,the more mixed gas.Same wih the aerated growth rate.The results from the stepped simulation is completely consistent with the experimental results.Having the same flow rate,the water flow will switch into the falling mode from its original sliding mode wilh the increase of its step size.The pressure of horizontal section will firstly decrease and then gradually increase from the concave portion to the convex portion,With the increase of upstream heads,the pressure level of the horizontal section will also increase.The pressure of its vertical section will decrease from the bottom to the top and it will finally reach its max level at the concave point of the step.Correspondingly,the maximum of negative pressure will appear at the lower edge of its convex point which is at the top of the step.