The Eddy-prevention Methods In The Closed Sump Of Pumping Station By CFD

The open sump had characteristic with low flow, variable water level, and was easy to form free water vortex. The concrete plate was added to the open sump to avoiding free water vortex. This type of sump was defined as the closed sump. The closed sump could avoid the forming of surface vortex and decrease the intensity of vortex. However, the harm caused by vortex in the sides and bottom wall still exist in the closed sump.CFD numerical simulation was used to simulate and solved the vortex problem by designing different schemes.The effect of eddy-prevention and hydraulic performance was as evaluation index.The results could be applied to eddy-prevention fields in closed sump and was useful to the operating stability of pump station.(1) Commercial software ANSYS 14.5 was used to simulate the vertical type pump station. The total mesh nodes’number was 1.1 million, which was chose by mesh independence experiment. Compared with different turbulence models, standard k-ε turbulence model was used to do numerical simulation.(2) To research the hydraulic characteristics of eddy-prevention methods behind the bell mouth attached to the wall of the closed sump, the CFD numerical simulation was used to research the different impact of eddy-prevention and hydraulic performance by changing the pillar height, pillar diameter, pillar shape, baffle slope and the shape of back wall with the suction sump.Numerical calculation shows that, increasing pillar height can prevent vortex; Increasing the pillar diameter can press the water to the behind of bell-mouth better, improving the flow pattern; Contrast to the circle and diamond pillar, the eddy-prevention effect of the square pillar was better; With the decrease of the baffle slope i, the vortex region was compressed upwards, the intensity of vortex has subsided, but the vortex has not been completely prevented, with the decrease of the baffle slope i, the pumping head and efficiency showed a trend of decrease after the first increase; Adopting the semicircle and symmetric volute can remove the two corner vortex where are most likely to form, the symmetric volute form conforms to the requirements of the water flow best, and the vortex after the above of the bell-mouth was prevented, its corresponding hydraulic performance and the velocity uniformity are characterized higher. Combined with the eddy-prevention, w-shaped back wall was the first choice to the closed sump.(3) To research the hydraulic characteristics of eddy-prevention methods under the bell mouth attached to the bottom of the closed sump, the CFD numerical simulation was used to study the impact of the height of triangular guide cone, the radius of triangular guide cone, the conical face shape of triangular guide cone, the height of trapezoid platform guiding cone, the radius of trapezoid platform guiding cone, the conical face shape of trapezoid platform guiding cone, the length of the cross plate, the height of the cross plate, the angle of the cross plate on preventing eddy. The numerical simulation shows that triangular guide cone can prevent eddy, but the high triangular guide cone have effect on water flowing into the bell mouth, small radius of triangular guide cone have little effect on guiding water flowing into the bell mouth. The ellipse conical face shape of triangular guide cone was more correspond with streamline and there was no bad flow pattern. Trapezoid platform guiding cone could prevent the bottom vortex. The high trapezoid platform guiding cone can influence water flowing into the bell mouth. With the increasing radius of trapezoid platform, the streamline on conical face becomes uniformity, the changes of efficiency and pump head are not obvious. The pressure on ellipse conical face decrease gradually, flow velocity increase uniformly. The streamline of conical face match with the shape. The cross plate did not well in eddy-prevention. The long cross plate will lead to water flow into bottom of the cross plate through surface. The efficiency and pump head would decrease with the height of the cross plate increasing. When the cross plate was too high, it will increase the interfere to water flow under the bell mouth. The bottom vortex was founded in the bottom of the high cross plate. The bottom vortex will move from the bottom to the outside of the cross plate. With the angle between the cross plate increasing, when the angle was 90°, the cross plate can effectively improve flow regime and eddy-prevention.(4) The closed sump was added eddy-prevention methods, which had little effect on hydraulic performance. Engineering application showed that eddy-prevention methods ensure pumping station running steady. Vibration and noise were significantly reduced.Steady flow and model test show that the eddy existence in the back of the bell mouth. Compared with the hydraulic performance, the CFD numerical simulation was verified as valid.