Research On Elimination Measures Of Harmful Vortex At X-shapes Conduit Inlet Of Bidirectional Pumping Station In Weicun Junction

Weicun junction project is a large-scale project combining water conservancy and shipping.The hub project adopts the form of parallel arrangement of ship lock,sluice and bidirectional pumping station.The center line of the pumping station is far from the center line of the river,so the water flow from the river to the pumping station needs to make a large turn,and the water flow conditions are complicated.When the pumping station under parallel arrangement of sluice and pumping station is in operation,there is an angle between the flow direction of the water flow into the forebay of the pumping station and the center line of the forebay,which easily leads to the transverse velocity in the forebay of the pumping station.In serious cases,the air-core vortex will be generated,affecting the safe and stable operation of the pump unit.Therefore,certain engineering measures should be taken to eliminate harmful vortices at the inlet of the inlet passage.At the same time,the flow velocity distribution uniformity and the flow average angle at the inlet section of the inlet passage should be improved as much as possible to ensure good inlet conditions for the pump unit.Taking the forebay of the bidirectional pumping station of Weicun junction project as the research object,this paper uses the three-dimensional numerical simulation software FLUENT to simulate the three-dimensional turbulent flow pattern of the forebay flow of the bidirectional pumping station under drainage and diversion conditions based on the N-S equation and standard k-ε turbulence model.Based on the analysis of the forebay flow pattern of the original scheme of the pumping station under different startup combinations,the measures of eliminating harmful vortex at the inlet of the inlet passage by combining partition wall and baffle are put forward,and the numerical simulation is carried out.The specific research results of this paper are as follows.（1）When the original scheme of the forebay of the bidirectional pumping station of Weicun junction project is under different startup combinations,there are large transverse velocity and vertical vortex before the inlet passage of each pump units.When the vortex is serious,it is likely to entrap air into the pump unit and affect the safe and stable operation of the pump unit.Under the influence of transverse velocity before the inlet of the inlet passage,the velocity distribution uniformity of inlet section of each inlet passage is 71.38%～86.61%,and the average flow angle is 79.11%～87.97%in the drainage condition.The velocity distribution uniformity of inlet section of unit 1#where is near the control gate is the lowest when 5 units are fully open.The average flow Angle of inlet section of unit 2#is the lowest.Under diversion condition,the velocity distribution uniformity of inlet section of each inlet passage is 79.83%～87.27%,and the average flow angle is 86.74%～88.87%.When only unit 5#is opened,the velocity distribution uniformity of inlet section and the average flow Angle are the lowest.（2）The trash rack bridge pier is connected with the partition block between the corresponding units to form partition wall.When 5 pump units are fully open,the average flow Angle of the inlet section of each inlet passage is 86.68%～88.19%,which is significantly improved compared with the original scheme.The partition wall which is in front of the inlet passage of each pump unit is beneficial to reduce the transverse velocity,but there is still vertical vortex above the front of the inlet passage.（3）Shortening the length of the diversion partition wall between the sluice and the pumping station can reduce the range of the vortex area at the head of the diversion partition wall which on the side of the pumping station.Shorten the head of the diversion partition wall to be flush with the head of trash rack bridge pier can eliminate the vortex;The diversion pier which is in front of the trash rack bridge pier corresponding to the two unilateral pump units can effectively improve the velocity distribution uniformity and the average flow angle of the inlet section of the unilateral unit’s inlet passage,but the vertical vortex still exists above the front of the inlet passage.（4）The horizontal position,bottom elevation and horizontal dip angles of the vertical baffle have significant effects on the flow pattern before the inlet passage.As the distance between vertical baffle and inlet section increases,the average flow angle of inlet section of each inlet passage increases,but velocity distribution uniformity decreases.At the same time,the range of vertical vortex above the inlet of each inlet passage decreases.When the distance between the vertical partition and the inlet section of each inlet passage is 12m,the vertical vortex above the inlet passage of each pump unit is eliminated;There is no vertical vortex above the front of the inlet of the inlet passage at different bottom elevations of vertical baffles.With the increase of bottom elevations,the velocity distribution uniformity at the inlet section increases but the average flow Angle decreases.When the bottom elevations are-1.38m,the average flow angle at the inlet section of inlet passage basically stays the same and the velocity distribution uniformity is good;There is no vertical vortex above the front of the inlet of inlet passage at different horizontal dip angles of baffles.Decreasing the horizontal dip angle of baffles can effectively improve the velocity distribution uniformity,but it has little effect on the average flow angle.When the horizontal dip angle is 30 degrees,the velocity distribution uniformity at inlet section of inlet passage is better;Adding baffles in the front tank of the bidirectional pumping station has little influence on the head loss when it is used as outlet channel.（5）The three-dimensional flow numerical simulation of the forebay flow pattern what is the proposed scheme under different startup combinations of the drainage and diversion conditions in Weicun junction project is carried out.The results indicate:the proposed scheme of improving the flow pattern of the forebay can achieve the goal of eliminating the harmful vertical vortex and ensuring the stable operation of the water pump unit under different startup combinations.In this paper,elimination measures of harmful vortex which in the inlet passage of pumping station under parallel arrangement of sluice and pumping station are studied,which has important reference significance for similar water conservancy projects.