| The inlet sump is an important part of the city's pumping station.It is an important structure connecting the pumping station's front sump and the pump.If the pumping station's influent water flow disorder will seriously affect the pump's water inlet conditions and reduce the pump efficiency.Due to different starting conditions,the flow state of the pump station is complicated,which affects the safe operation of the pump.Therefore,through certain measures to improve the inlet water flow state of the pumping station,it can provide good water inlet conditions for the water pump to absorb water.In this paper,based on the actual background of the Nanjing Qiqiaoweng water pumping station,based on the CFD numerical simulation method,the influent flow state of the pumping station under different starting conditions is analyzed.The effects of rectification measures such as columns,grids and water conducting cones on the improvement of the influent flow state of the pumping station are mainly studied.(1)Using the large commercial software ANSYS,numerical simulation of the entire Qiqiaoweng pumping station is carried out.Through the grid-independent analysis,the total number of grids in the pumping station is determined to be 1.2 million.Through the comparison of different turbulence models,the turbulence model is determined as the standard k-? model,and the hydraulic performance of the pumping station is predicted and compared with the field measured performance.When there is no rectification,the units 1 and 2 are operated(operating condition ?),and the water flow in front of the inlet of the pumping station is affected by the wall resistance.There are two recirculating zones with opposite symmetry and opposite rotation directions near the inlet pipe.The influent flow pattern is uneven and very disordered,and there is a large deflection of the streamline near the pier.Unit 3 is operated separately(operating condition ?).Although the recirculation zone near the inlet pipe of the pumping station is significantly reduced,the inflowing water flow is more disordered,the streamline is more curved,and the de-flow phenomenon in the sump is serious.The streamline near the pier is very uneven and the water flow is severely skewed.(2)Based on the numerical simulation of CFD,the effects of column and conventional grid on the improvement of influent flow state and hydraulic performance are studied.The calculation results show that:1)the distance between the column and the back wall of the sump.When operating condition I,when the distance is too close(0.4L0),the water flow is disturbed by the column and then redistributed.The flow velocity of each part of the bottom layer,the middle layer and the surface layer of the longitudinal section I fluctuates greatly,and the flow velocity difference is different at different positions of the same section;When the distance is far(0.8L0),the low-speed area in the upper left corner of longitudinal section ? has a smaller trend,and the rectification effect is better.The velocity distribution of the bottom layer,the middle layer and the surface layer of the longitudinal section? is more uniform than that without rectification measures,which effectively reduces the distance.The flow velocity at the side wall of the pier is better.When operating condition?,when the distance is too close(0.4L0),the column not only does not perform rectification,but worsens the flow state around the pump body;when the distance is far(0.8L0),the water flows through the column and then redistributes and enters the water.The drift in the sump is reduced and the rectification effect is the best.2)Column width.When operating condition ?,when the width is 0,125D0,the column spacing becomes larger,and the flow velocity distribution is basically the same as that of the unrectifying measure.When the width is increased to 0.25D0,the water is redistributed after passing through the column,and the column is arranged at a long distance(0.8L0),so that the water flow has a large space for energy exchange and flow rate adjustment,and the water flow line is smooth,However,when the width is too large to 0.4D0,the pitch becomes small,so that the flow area of the water flow is reduced,and the flow state after the column is disordered,and the flow state in the water sump is further deteriorated.When operating condition ?,the flow state of the pumping station is basically the same as that of the operating condition 1.3)Number of columns.When operating condition ?,when the number of columns is N=2,the interval between the columns becomes larger,resulting in vortex near the column,the flow stream is bent more,and the column does not rectify.When the number of columns increases to N=6,the interval becomes smaller,and the flow line is evenly distributed after the water flows through the column,which can effectively reduce the flow velocity on both sides of the longitudinal section ? and reduce the speed difference on the section.The uniformity of flow velocity distribution in the inlet sump with the number of columns N=6 is significantly improved.4)Grid rectification measures.Compared with the no-rectification measures,the flow velocity distribution on the cross-section ? of the bottom plate in the inlet sump is relatively uniform,but as the water depth increases,the flow line becomes turbulent,the flow velocity distribution is asymmetrical,and the flow state improvement in the inlet sump is not obvious.The axial flow velocity uniformity of the longitudinal section ? is increased after the addition of the grid.(3)Through the CFD,the influence of the height of the triangular water guide cone and the bottom diameter of the water guide cone and the 1/4 elliptical water guide cone on the hydraulic performance of the unit are studied.The calculation results show that:1)the height of the triangular water guide cone.Under operating condition ?,for the units 1 and 2,the height of the water guide cone is 0.35D0,the improvement of the flow state under the horn tube is not obvious.After the height of the water guide cone increases to 0.5D0,the horn tube two The side water bodies are symmetrically distributed as a whole.Under operating condition ?,for unit 3,the trend of the flow pattern under the horn tube after the water guiding cone is set is basically the same as that of units 1 and 2.2)The bottom diameter of the triangular water guide cone.Under operating condition ?,for the units 1 and 2,the smaller the diameter of the water guiding cone is 0.4D0,the improvement of the flow state below the horn tube is not obvious.When the bottom diameter of the water guide cone is 0.6D0,it can effectively fill the flow disorder area under the horn tube,and guide the water flow in the lower left of the horn tube into the horn tube,and the water flow on both sides shows a symmetric distribution trend.Under operating condition ?,for unit 3,the flow improvement effect is best when the bottom diameter of the triangular water guide cone is 0.6D0.3)1/4 elliptical water guide cone.Under the same height and bottom diameter conditions,the 1/4 elliptical water guiding cone and the triangular water guiding cone improve the flow capacity under the horn tube in two operating conditions,and the 1/4 elliptical water guiding cone is also It can improve the uniformity of flow velocity distribution in the flare tube,but the lifting range is slightly lower than the triangular water guiding cone.(4)This paper mainly studies different rectification measures to improve the influent flow state of the pumping station.Adding a column in the inlet sump and setting a water guiding cone under the horn tube can effectively improve the influent flow state.It is recommended that the column is arranged at a distance of 0.8L0 from the back wall of the inlet sump,the width is 0.25D0,the number is 6,and the height of the triangular water guide cone is set to 0.5D0 under the bell tube,and the bottom diameter is 0.6D0,which is a superior solution,meeting the actual needs of the project. |
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