The Numerical Simulation Study On Off-grid Turbulence Characteristics Of Grid Flocculation Tank Based On CFD

In 2006 the Ministry of Health and the National Standardization Management Committee released a new "Standards for drinking water quality "。The old to the new standard can not be realized Water turbidity 1NTU requirement,eliminating the need to implement the upgrading of the waterworks.The enhanced flocculation method is an effective way to improve the water quality. Through analysis of the mechanism of coagulation kinetics and water flow.The main contents of this paper are:1,Conduct numerical simulation of turbulent flow field inside a single shaft in grid flocculation tank by means of CFD software, and to optimize the design of grid flocculation tank.2,Analysis off-grid turbulence flocculation characteristics of grid flocculation tank, Determine the best spacing of single grid platets and double-grid platets.This paper established a sound analysis model of a practical engineering single shaft, made use of k-εmodel, and in the local strong-turbulence region used encryption grid way to ensure simulation accuracy.Through the graphic curve drafted by the single and double trash rack plate numerical simulation results, use simulation evaluation index--turbulent kinetic energy k, turbulent kinetic energy dissipation rateε, vortex velocity gradient G and"Flocculation effective body".1,In the shaft, adding grids can change the whole flow field flow state; changing grids density and increasing the number of girds are able to increase the turbulent kinetic energy. We could control the size and intensity of the water vortex to ensure the formation of dense flocs. The imported flow rate at the speed of 0.13m / s and the grid layouts with grid spacing of D = 40mm or 50mm have higher turbulent kinetic energy level, strong differences in the pace. The double-gate plate makes theave turbulent flow and floc concentration homogenization along the flow cross-section so that in the whole cross section there is enough floc concentration, which increases"Flocculation effective body"of grid flocculation tank;2,In the double trash rack plate layout, the turbulent kinetic energy makes the floc reasonable collision and provide a reasonable range of 50-70cm for the spacing of the growing trash rack plate. This paper indicated that reasonable space 50cm is the best for double-spaced grid plate.In this paper, we conducted limited study on pattern of flow and flow distribution and characteristics of flow field. The analysis on the simulation results can guide the design work and provide new methods.