Numerical Study Of Sandstone Wastewater Of Hydropower Stations In A Vortex-type Grit Chamber By Large Eddy Simulation

High turbidity wastewater is produced during the processing of sandstone aggregates in powerhouses and can result in environmental pollution and channel deposition. Therefore, it is imperative to treat sandstone wastewater to protect the quality of receiving water.In this paper, the Eulerian-Lagrangian large eddy approach coupled with VOF (Volume of Fluid) was applied to study flow of the sandstone wastewater of hydropower stations in a vortex-type grit chamber, and the internal flow mechanism,the particles motion law, the influence of blade structures and operating parameters of the vortex grit chamber were discussed, furthermore blade rotating speed, blade quantity, and the distance between the impeller and the bottom are studied.(1)Eulerian-Lagrangian LES (Large Eddy Simulation) coupled with VOF method of high concentration sandstone wastewater was established in a vortex-type grit chamber.Aiming at the gas–liquid–solid multiphase flow in vortex-type grit chamber with complex free surface and flow pattern, Eulerian-Lagrangian large eddy numerical simulation coupled with VOF method of high concentration sandstone wastewater was established. The turbulent flow of liquid was modeled using the LES model, the interface between the liquid and air core was modeled using the VOF multiphase model, and particle flow was simulated by the stochastic Lagrangian model.(2)The solving method of mathematical model, the grid and reasonable boundary conditions were obtained.Closure of the subgrid-scale stress model was achieved using the static Smagorinsky model. The unsteady three-dimensional interaction between rotating impeller and fixed region in a whole flow field was numerically investigated with QUICK scheme, PISO algorithmic and sliding mesh technology. Reasonable boundary condition was employed by increasing calculation domain.(3)The VOF distribution, flow pattern, and particle distribution were analysed in vortex-type grit chamber.The gas–liquid–solid multiphase flow in vortex-type grit chamber was studied under the best working conditions, which was got from the experimental results. The result shows that the water surface fluctuations are observed, and the fluctuation is stronger in the process of water filling than the end of water filling. The water surface is low in the middle region of the chamber, and in the outer region of the chamber the water surface is high.The changing process of the liquid large eddy structure was discussed, and the flow filed simulated by LES was compared with that by the RANS. The result shows that LES can better reveal the turbulent phenomenon in the vortex grit chamber.The sensitivity of particle behavior to the collision force was studied, and particles distribution and particles trajectory are obtained. The results show that the particle performance is different with different particle size. The particles smaller than 10μm are hardly to be removed because they easily follow large eddy flow. The majority of particles larger than 50μm rapidly settle to the sludge hoppers of first-stage vortex grit chamber. Small part of particles smaller than 10μm are removed in the second-stage vortex grit chamber when the impeller speed is 50r/min, the HRT (Hydraulic Retention Time) is 20min.(4)The influences of blade structures and operating parameters, including blade rotating speed, blade quantity, and the distance between the impeller and the bottom were studied.The best condition is achieved that blade rotating speed is 105rap/min,impeller number is 4, the distance between the impeller and the bottom is 120mm.