Research On Hydraulic Performance Improvement Of Inlet Flow Pattern Of Small And Medium-sized Irrigation And Drainage Pumping Station

By serving agricultural irrigation and drainage,irrigation and drainage pumping station has become the important public infrastructure for China's economic and social development,which has played a huge role in improving agricultural production conditions,guaranteeing food security and promoting rural economic development,farmers' income,rural drinking water safety.Irrigation and drainage pumping station's intake construction contains forebay and intake sump.Forebay is set to ensure water's diffusing from approach channel to intake sump smoothlyand provide outstanding flow pattern for intake sump.Open intake sump has free water surface which used in the middle and small pumping station for sucking water.Intake sump is used to adjust the flow pattern and supply excellent suction condition for the pump.The flow pattern in the forebay and intake sump directly effects pumping station operation.In this paper,by using CFD,model test and local measurement,flow in the forebay and open intake sump,influence of the structure,anti-swirl method and hydraulic optimization on closed intake sump are analyzed.The outcome can be applied to the similar pumping station.(1)To get the suitable turbulent model,several turbulent models which contains of Standard k-? turbulent model,RNG k-s turbulent model,Realizable k-s turbulent model and SST turbulent model,are applied to solve the governing equations,so that the prediction results are compared to experiment results,and Standard k-s turbulent model is the final chosen turbulent.By analyzing the mesh quantities of forebay of irrigation and drainage pumping station,the suited mesh quantity is 0.16 million.The intensity of flow wake behind the double row columns is stronger than that behind single row columns,so the double row columns are better in restraining recirculation area in forabay.The location of columns have significant effect on the flow pattern.The flow pattern is impacted by the Carmen vortex behind the columns,while the location of columns is near the intake sump.It is recommended that the column is located at the distance of 0.45B from the entrance to the intake sump.The cross-section size of column is also animportant factor to the result of rectification,and the recommended size is 0.0375B.The height and shape of column have little influence on the velocity distribution in the forebay,and the recommended height of column is 0.8H.The research shows that it is useful to set column in the forbay,because the column can rectify the flow pattern in the forebay.The rotation of flow through the column make the velocity of water be re-distributed,and that,the flow tends to be uniform and smooth.So that the recirculation area is restrained and the velocity of water before intake sump is re-distributed.The intake sump get better flow pattern after column setting.(2)The flow field distribution and 3-D flow pattern is simulated by CFD in the intake sump of pump station.There is little difference about flow pattern in intake sump in different flow rate condition.There is a quadratic linear relation between hydraulic loss and flow rate.The simulation calculation method is applied to research the influence of hydraulic performance and flow pattern by change single factor of different geometric parameters.There are three conclusions can be got in this research.1)The good flow pattern result from the suitable range of main structural size of intake sump,which ensure the good velocity distribution in the inlet of pump.The suitable width of inlet sump is 3-4D,because the narrow width of intake sump can result in the high hydraulic loss and the big streamline curvature around bell mouth,which lead to vortex in intake sump.Also,the big width will result in bias flow and recirculation,and that can lead to vortex in intake sump.2)The increasing of velocity on the surface leads to bad flow pattern in intake sump and high hydraulic loss in the condition of over low submerged depth of bell mouth.In the other condition,over high submerged depth cost much investment for the increasing of digging depth of intake sump.3)The water flow through bell mouth to get in impeller chamber,so the shape of bell mouth has a significant influence on pump hydraulic performance.Research result shows that the shape of bell mouth has an influence on the pressure distribution of suction tube and the uniformity of water flow velocity.The recommend shape of bell mouth is 1/4 times circle.The recommend diameter of bell mouth is 1.5D.(3)Calculation results show that efficiency of pump set will change a little and the flow pattern in the sump will be effected when pump beam,maintenance platform and breast wall is added in the open intake sump separately.When the pump set is added in the open intake sump,the flow pattern in the intake sump changes a little.When the width of the pump beam increases and maintenance platform is set on the back of intake pipe,the flow pattern in the sump get worse,disordered flow happens around the bell mouth and back wall.When the breast wall is set in the intake sump,the water is squeezed vertically by the breast wall,then the way of flow on the surface in the sump is changed,the bell mouth suck the water with the unidirectional way.Discharge effects the pressure distribution on the vertical profile a little.When the breast wall is added,the axial velocity on the suction pipe will change a lot.(4)9 kinds of anti-vortex methods such as diversion wall at the bottom of intake sump,diversion column under the water and diversion plate on the back wall is installed in the intake sump,flow pattern in the intake sump is numerically analyzed.The research results show that:1)Velocity near the back wall is small.Flow in the intake sump is complex.Two symmetrical recirculation zone maybe happen which will result into surface vortex.Vortex zone maybe occur near the bottom of side wall.Low velocity recirculation zone exists near the bottom of the back wall center which will result into plane wall vortex.2)When horizontal cover plate is applied,distance from the back wall decreases.Surface vortex behind the nozzle is prevented pumping into the bell mouth,which will reduce the probability of bottom vortex.3)When ? type cover plate is set on the bell mouth,the flow pattern improves a little,obvious recirculation zone happens on the side wall and the both sides of vertical plate of ? type cover plate.4)Cover plate above water will improve the suction condition of pump,but spiral flow probably happen below the cover plate of the nozzle which not benefit flow adjustment on the back wall.5)Diversion wall at the bottom of intake sump will prevent the formation of singular point zone effectively.Recirculation zone maybe exist at the side wall and back wall of the intake sump.Obvious gathering streamline and singular point zone occurs at the back wall.There is no improvement for the flow pattern in the intake sump.6)When the diversion plate is added,distance from the back wall decreases which will enhance the unidirectional suction.Vortex at the corner of the intake sump aggravates.Anti-swirl effect is not ideal.7)Vortex happens at the side wall,back wall and the bottom the rectangular diversion plate.8)When the circle diversion column is installed,there is no new recirculation zone,but the flow pattern will not be improved.9)The vertical diversion plate will result into the unidirectional suction for bell mouth and disordered flow behind the suction pipe.10)The declining diversion plate will result into the unidirectional suction for bell mouth.Velocity decreases on the back wall of suction pipe.Back wall vortex is suppressed.Circulation maybe happen around the declining diversion plate.(5)The hydraulic design rules of a pump station are given to reconstruct the open-style intake sump to closed-style intake sump by numerical simulation,model test and field test.1)An integrated pump station is simulated to analyze and compare the hydraulic performance of original scheme in different flow rate condition.Furthermore,the factors of width,distance fromback wall,bottom clearance and shape of back wall are simulated to get hydraulic optimization.The optimization results,in other words,are design rules to closed-style intake sump reconstruction.2)With the increase of pool width,the pumping station efficiency will increase from the calculation of hydraulic performance.But the over big width of intake sump leads to bias flow and recirculation,further vortex,in intake sump.On the other hand,the over small width of intake pump results in high hydraulic loss and bad flow pattern around bell mouth.The recommended width of intake sump is(0.25-3)DL.3)With the increasing of distance from back wall,the efficiency increases and reach the peak point until that TID equals to 0.5.The over small distance from back wall results in bad uniformity of flow velocity and large hydraulic loss of bell mouth.On the other hand,the over large distance from back wall may lead to air-core vortices for the increasing degree of freedom.The recommended distance from back wall is(0.4?0.7)DL· 4)The suitable bottom clearance is essential for bell mouth to suck water around it.The over high bottom clearance not only cost high investment in civil construction,but also make bell mouth suck water in single side.Further,that situation leads to bad uniformity of velocity in pump inlet and decrease the energy and cavitation performance.On the other hand,the over low bottom clearance leaves small space for lager water to go through and that leads to high hydraulic loss and bade flow pattern in pump inlet.So the recommended bottom clearance is(0.5?0.7)DL·5)The circle back wall and co-style back wall are simulated to analyze the influence on hydraulic performance on the base of optimizing geometric parameters.The calculation results show that the flow pattern in the ?-style back wall scheme is better than that in original scheme.6)The result predicted by CFD is consistent with the result of model test,and the result of CFD calculation is credible.7)According to result of field test,the degree of noise and vibration of pump station meet the national standard requirement.The measured flow rate is over the design flow rate in design head point.The results of CFD calculation and model test are successfully applied to a pump station,which have good application value.