Method for improving flow state of pump station inlet by using bridge pier flow guide of trash remover

Abstract

The application provides a method for improving flow state of a front pool of a gate station combined pump station by using a trash cleaner bridge pier guide, and belongs to the technical field of pump station engineering, and comprises the following steps: a trash cleaner bridge is arranged at the front end of a guide wall on both sides of the downstream of the gate station combined pump station, and the trash cleaner bridge is supported by multiple pier wall type piers; a straight bridge pier is arranged in the middle of the front pool, the bridge pier is parallel to the longitudinal center line of the front pool; the outer piers are symmetrical to each other relative to the longitudinal center line of the front pool, and the outer piers adopt an "eight" shaped bridge pier, the horizontal center line of the bridge pier is deflected outward along the water flow direction, the flow direction axis and the flow velocity are adjusted, the low speed area of the front pool is reduced as the target, the deflection angle of each group of symmetrical "eight" shaped bridge piers is optimized through CFD numerical calculation and analysis on the flow field of the downstream of the pump station, especially the front pool, the flow state of the front pool is greatly improved, the area proportion of the low speed area is reduced from more than 10% to less than 1%, the silt accumulation is avoided, the deflection of the water inlet of the side unit is eliminated, and the energy efficiency of the pump device is improved.

Description

Technical Field

[0001] This invention belongs to the field of pump station engineering technology, and in particular to pump station-sluice gate combined engineering, and relates to a method for improving the inflow state of the pump station combined with the sluice gate by using the bridge pier of the cleaning machine bridge. Background Technology

[0002] Large rivers in my country's plains typically require flood control, navigation, and irrigation functions, necessitating the construction of sluice gates and pumping stations to control water levels in sections. To save land and construction costs, dams are usually built, with sluice gates and pumping stations arranged in parallel along the dam body, forming a water conservancy hub. To ensure symmetrical water flow, pumping stations are usually located in the middle of the dam, with sluice gates symmetrically arranged on both sides. Guide walls are installed downstream of the pumping stations at the boundary between the pumping stations and the sluice gates to ensure the appropriate flow pattern at the pumping station intake.

[0003] However, in practice, in combined sluice gate and pumping station systems, the flow cross-section in front of the guide walls on both sides downstream of the pumping station is very wide, including the sluice gate sections on both sides. The flow suddenly narrows from this wide cross-section to the forebay area between the two guide walls, causing large low-velocity vortex zones to form in the forebay areas near the guide walls, and significant lateral flow in front of the inlet channels of the two pumping units. The flow within the forebay is extremely uneven and non-axial, resulting in significant siltation and affecting the pumping station's efficiency. Therefore, there is an urgent need to invent a technology to improve the flow pattern in the forebay of combined sluice gate and pumping station systems, eliminate siltation, and enhance pumping station efficiency. Summary of the Invention

[0004] Purpose of the Invention: The purpose of this invention is to overcome the shortcomings of conventionally designed gate-pump combined forebays, such as large-area vortex low-velocity zones and high lateral flow velocities in front of the side inlet channels, which lead to large-area siltation in the forebay and low energy performance of the pumping unit. Addressing the need for a sludge removal bridge to install a trash rack and sludge removal machine at the pumping station inlet, this invention proposes a method to improve the flow pattern in the forebay by installing a sludge removal bridge at the front end of the downstream guide wall of the gate-pump combined forebay and optimizing the direction of the bridge piers, thereby avoiding siltation in the forebay and improving the efficiency of the pumping station.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for improving the inflow pattern of a combined sluice gate and pumping station by using a bridge pier for flow diversion includes the following steps:

[0007] A. CFD analysis of the forebay flow in Scheme 1, where only a guide wall is installed downstream of the combined sluice gate and pumping station:

[0008] The stationary velocity of sediment is the critical flow velocity at which sediment in a water flow changes from motion to stillness. Its calculation formula is as follows:

[0009]

[0010] In the formula: U S The stationary velocity of sediment flow is given in m / s; ρ s The density of sediment is kg / m³ 3 ρ is the density of pure water, kg / m³ 3 g is the acceleration due to gravity, m / s² 2 d represents the median particle size of suspended sediment, in meters.

[0011] The initiation velocity of sediment is the critical flow velocity at which sediment on the riverbed transitions from rest to motion under the influence of water flow. Its calculation formula is as follows:

[0012]

[0013] In the formula: U e ρ is the initial velocity of sediment flow, m / s; h is the average water depth, m; ρ is the initial velocity of sediment flow. s The density of sediment is kg / m³ 3 ρ is the density of pure water, kg / m³ 3 g is the acceleration due to gravity, m / s² 2 ; d is the median particle size of suspended sediment; m.

[0014] The inlet section is a straight section of the river channel 5-8 times the water depth downstream of the sluice gate, and the outlet section is a straight section of the inlet flow channel for all operating units of the pumping station. The computational domain also includes an air domain 2m above the water surface. The computational domain is divided into unstructured meshes using Mesh, with the prototype global maximum size not exceeding 1m. The meshes are densified at the inlet, outlet, and water surface of the computational domain, and the number of meshes needs to meet the independence verification.

[0015] The computational domain is defined by a given mass flow rate at the inlet and outlet, and the solid boundary is set to a no-slip wall.

[0016] The computational model considers the influence of gravity and performs CFD (Computational Fluid Dynamics) calculations on the water flow in the computational domain downstream of the pumping station. The water surface is captured using the VOF (Volume of Fluid) method. The calculation results are post-processed to obtain the flow velocity and streamline distribution in the computational domain, including the forebay of the pumping station. The flow regime in the forebay is observed, and formula (1) is used to determine the location and size of the sedimentation zone in the forebay. Formula (2) is used to determine the location and size of the area in the forebay where sediment has accumulated and cannot be flushed away. The severity of sedimentation in the forebay is expressed as the percentage of the sedimentation area to the total area of ​​the forebay. Formula (3) is used to calculate the proportion of the low-velocity sedimentation zone in the forebay.

[0017]

[0018] In the formula: λ is the proportion of the low-velocity zone in the forebay where the flow velocity is lower than the sediment stagnant velocity; Al The area of ​​the low-velocity zone of the forebay inside the guide wall, in m 2 A t The total area of ​​the forebay inside the guide wall is m. 2 .

[0019] When all units of the pumping station are running, the flow in the forebay of Scheme 1 is turbulent, and there is a large area of ​​low-velocity vortex zone inside the guide wall. The flow velocity in the low-velocity vortex zone is lower than the sediment stagnant flow velocity, which will cause sediment accumulation. The backflow of the low-velocity zone on both sides of the forebay squeezes the main flow, causing severe lateral flow deviation in the inlet channels of the units on both sides, except for the middle unit.

[0020] B. Location selection for the inlet cleaning machine bridge of the combined sluice gate and pumping station – located at the front end of the downstream guide wall:

[0021] For pumping stations located on river channels, there are three options for the placement of the trash rack bridge: First, it can be placed at the inlet of each pump unit, with one trash rack bridge per unit. However, this method directly affects the flow pattern and performance of the pump unit due to the increased resistance to debris, and is rarely used now. Second, it can be placed on the downstream section of the diversion channel, which is currently the common practice for pumping stations located on river channels. However, for pumping stations combined with sluice gates, if the trash rack bridge is placed on the diversion channel, when the sluice gates are opened for flood discharge, the water flow direction is opposite to the water flow direction when the pumping station is pumping water. The large flow rate and the large amount of incoming debris can cause backflow blockage of the trash rack. Since the trash rack does not have the function of reverse debris removal, the trash rack and the trash rack must be lifted up during flood discharge to prevent debris from being intercepted in the water, greatly increasing the cost of engineering equipment and the difficulty of operation and management. Furthermore, when the pumping station switches to pumping operation, aquatic plants and other debris in the river channel between the cleaning machine bridge and the pumping station can flow with the water flow and enter the pumps, causing blockages. This can reduce pump flow or even break pump blades, seriously affecting the safe operation of the pump unit. To solve these problems, a cleaning machine bridge is installed between the heads of the two guide walls in the forebay of the pumping station, equipped with a trash rack and a cleaning machine. This prevents debris from entering the pumps during pumping and removes it promptly, avoiding any impact on the flood discharge of the control gate. Simultaneously, the cleaning machine bridge uses pier-wall type piers with streamlined, low-resistance heads and tails, symmetrically arranged relative to the longitudinal centerline of the forebay. The cleaning machine bridge piers guide the flow, adjusting the axial direction and uniform flow velocity, thus improving the flow pattern in the forebay.

[0022] C. A cleaning machine bridge is installed at the front end of the downstream guide wall of the sluice gate and pump station, with straight piers for the cleaning machine bridge – Calculation and effect of the flow pattern improvement in the forebay under Scheme Two:

[0023] Since the vortex in the area on both sides of the forebay between the two guide walls downstream of the gate station and the pump station is caused by the sudden reduction of the cross-sectional area of ​​the water flow after entering the guide wall area, which causes the mainstream to contract, the straight piers are set at the front end of the guide wall. The straight piers are in the direction of the mainstream, and their length direction is perpendicular to the length direction of the bridge deck and parallel to the guide wall. This helps to prevent the forebay from contracting and forces the water flow to tend to flow uniformly along the axis of the forebay, thereby improving the flow in the forebay.

[0024] Using the method in step A, CFD calculations were performed on the downstream flow domain of the pumping station. The calculation results were then post-processed to obtain the streamlines and velocity distribution in the forebay between the two guide walls. The proportion of the area where the velocity is less than the velocity of the sediment stop flow was calculated. The flow direction before the inlet of the water pump was observed. Compared with the case where no cleaning bridge was installed, the proportion of the low-velocity area in the forebay was significantly reduced, and the flow deviation at the inlet of the water pump was significantly improved.

[0025] D. A sluice gate combined with the downstream guide wall of the pumping station is used to install a debris removal machine bridge, with the preferred "eight"-shaped piers for the bridge – Method for determining Scheme 3 and its effect on improving flow regime:

[0026] Considering the large spacing between the straight piers of the cleaning machine bridge at the downstream guide wall of the pump station in Scheme 2, due to the inertia of the inlet water flowing towards the center, the straight piers cannot completely eliminate the phenomenon of the inlet flow converging towards the center of the forebay. A large area of ​​low-velocity vortex zone still exists on both sides of the forebay. To further reduce or eliminate the low-velocity vortex zone on both sides of the forebay, using the horizontal longitudinal centerline of the forebay as a reference, the symmetrical straight piers on both sides are deflected outwards at a certain angle around the vertical centerline of the piers in the direction of water flow. The two symmetrical piers on both sides of the longitudinal centerline of the forebay are deflected at equal angles and in opposite directions. Looking down from the direction of the incoming flow, the pier on the left side of the longitudinal centerline of the forebay is deflected clockwise, and the pier on the right side is deflected counterclockwise. The symmetrical piers are distributed in a "V" shape. The "V" shaped piers guide the water flow to both sides of the forebay, eliminating the low-velocity vortex zone and improving the flow pattern in the forebay.

[0027] The deflection angle of the symmetrical piers in the figure-eight shape is determined as follows: the middle pier located on the center line of the forebay does not deflect; multiple sets of symmetrical piers are set with deflection angles of 5°, 10° and 15° respectively. According to the order of the total deflection angle from small to large, the method of step A is applied to each combination of pier deflection schemes. CFD calculation is performed on the downstream water flow field calculation domain of the pump station. The calculation results are post-processed to obtain the streamlines and velocity distribution in the forebay between the two guide walls. The proportion of the area of ​​the region in the forebay with a velocity less than the sediment stop velocity is calculated according to formula (3). The flow direction before the water pump inlet is observed. According to the influence law of the pier deflection angle on the inlet direction and low velocity area of ​​the forebay, with the goal of reducing the area of ​​the low velocity vortex region in the forebay, the range of the optimal deflection angle of each set of symmetrical piers is determined. The pier deflection angle is further refined until the area of ​​the region in the forebay with a velocity less than the sediment stop velocity accounts for less than 1% of the area of ​​the forebay.

[0028] E. Comparing multiple options to determine the final optimal solution:

[0029] The proportions of the low-speed zone in the forebay of each scheme were compared. Finally, the preferred scheme was the bridge pier arrangement scheme with a low-speed zone area ratio of less than 1% in the forebay and the inflow deviation of the side unit inlet channel was basically eliminated.

[0030] Beneficial effects: This invention, by setting up a cleaning machine bridge at the front end of the forebay of the gate station and the pump station, and using the preferred "eight"-shaped bridge piers, guides the inflow into the forebay, prevents contraction, adjusts the axial direction of the water flow and makes the flow velocity uniform, eliminates the large-area vortex low-speed zone on both sides of the forebay and the inflow deviation of the water inlet channel, thereby improving the flow state of the forebay, avoiding siltation, and improving the energy efficiency of the pump station. Attached Figure Description

[0031] Figure 1 It is a schematic diagram of the layout of the gate station in conjunction with the downstream river channel of the hub, the fluid calculation domain, and the surface, middle and bottom layers of the water body;

[0032] Figure 2 This is a schematic diagram of the grid partitioning of the downstream fluid computational domain of the gate station and hub.

[0033] Figure 3 This is a diagram showing the flow lines and velocity distribution when the downstream guide wall of the gate station combined with the hub is 30m long and there is no cleaning machine bridge.

[0034] Figure 4 This is a schematic diagram of a conventional cleaning and sludge removal machine bridge arranged in the river channel downstream of the pumping station;

[0035] Figure 5 This is a schematic diagram of the cleaning machine bridge of the present invention arranged at the front end of the downstream guide wall of the gate station combined with the pump station;

[0036] Figure 6 This is a diagram showing the flow lines and velocity distribution when the downstream guide wall of the gate station and hub is 50m long and there is no cleaning machine bridge.

[0037] Figure 7 This is a diagram showing the flow lines and velocity distribution when the gate station is combined with the downstream guide wall of the hub, which is 50m long, and the front end is equipped with a straight bridge pier for cleaning and sludge removal machines.

[0038] Figure 8 This is a comparison chart of the low-velocity zone ratio of the pump station forebay for eight different schemes, with a 50m long downstream guide wall for the combined gate and hub.

[0039] Figure 9This is a downstream streamline and velocity distribution diagram of the preferred pier layout scheme of the present invention, which has the smallest proportion (0.4%) of the low-velocity zone in the forebay of the gate station combined with the hub pump station. Detailed Implementation

[0040] The following specific application case further illustrates the specific implementation of the present invention and verifies the provided technical solution. The main parameters of the gate station combined with the pump station and its forebay are as follows:

[0041] A pumping station in Jiangsu Province, such as Figure 1 The system adopts a combination of gate and pump station, with control gates at both ends and a pump station in the middle. It is equipped with 1800HD-10.5 type vertical guide vane mixed-flow pumps. After upgrading, TJ11-HL-05 hydraulic models were selected, with a rotational speed of 250 r / min and an impeller diameter of 1.68 m, totaling 5 sets. Five TL1600-20 / 2150 main motors are also installed, with a power of 1600 kW, for a total installed capacity of 8000 kW. The design flow rate per unit is 10.8 m³ / h. 3 / s, design head 9.5m, pump station design flow rate 54m³ / s 3 / s. Considering the diversion effect, two rows of guide walls are installed on both sides of the downstream pumping station section, perpendicular to the station building. The design pumping water level combination is: 21.5m upstream and 12m downstream. The downstream river channel layout is as follows. Figure 1 .

[0042] The method for improving the inflow pattern of a combined sluice gate and pumping station by using a bridge pier for flow diversion provided by the present invention in the above case includes the following steps:

[0043] A. CFD analysis of the forebay flow in Scheme 1, where only a guide wall is installed downstream of the combined sluice gate and pumping station:

[0044] like Figure 1 The sluice gate combined with the water conservancy hub is shown. The guide walls on both sides of the downstream section of the pumping station are each 30m long. The downstream flow computation domain mesh is as follows. Figure 2 When the grid number reaches 2.3 million, the grid independence condition is met. The CFD calculation results are processed to obtain the streamlines and velocity distribution downstream of the pumping station, including the forebay, as shown below. Figure 3 .

[0045] In formulas (1) and (2), ρ s =2650kg / m 3 ρ=1000kg / m 3 g = 9.81 m / s 2 Given d = 0.05~0.1mm, and the forebay water depth is 4.5m during pumping, substitute into equations (1) and (2) to obtain the sediment stagnant velocity U. S =0.06-0.1m / s, take U S =0.1m / s; initial velocity of sediment flow Ue =0.44-0.55m / s. When the water flow velocity in the river channel is lower than the stationary velocity, siltation occurs; when the water flow velocity is higher than the siltation initiation velocity, the silt can be washed away by the water flow.

[0046] Depend on Figure 3 It is known that during the operation of all units in the Scheme 1 pumping station, the flow in the forebay is turbulent, with a large low-velocity vortex zone near the inner side of the guide wall, the width of which is almost 50% of the width of the forebay. The flow velocity in the low-velocity vortex zone is lower than the sediment stabilization velocity, which will cause sediment accumulation; the backflow of the low-velocity zone on both sides of the forebay compresses the main flow, resulting in severe lateral flow deviation in the inlet channels of the units on both sides, except for the middle unit.

[0047] B. Location selection for the inlet cleaning machine bridge of the combined gate station and pump station – to be installed at the front end of the downstream guide wall.

[0048] The cleaning and sludge removal bridge is located on the downstream diversion channel of the pumping station, such as... Figure 4 This is the common practice in current river-blocking pumping stations; the cleaning machine bridge proposed in this invention is arranged at the front end of the two guide walls of the forebay, such as... Figure 5 As shown, a trash rack and a trash cleaner are installed in front of the trash cleaner bridge to prevent dirt in the water from entering the water pump during pumping, reduce the hydraulic loss of the trash rack and its impact on the pumping device, and at the same time avoid the impact on flood discharge.

[0049] The cleaning machine bridge at the front end of the forebay guide wall is constructed using bridge columns in the outer gate chamber area of ​​the guide wall. These columns are 0.8m in diameter and spaced 9m apart. The inner area of ​​the guide wall uses straight-line piers, each 10.8m long and 0.7m thick, spaced 4.15m apart. The pier heads and tails are streamlined, with a total of five piers symmetrically arranged relative to the longitudinal centerline of the forebay. Due to the significant length of the piers along the water flow direction, the guide wall was actually extended to 50m, with the front end serving as the pier.

[0050] C. A cleaning machine bridge is installed at the front end of the downstream guide wall of the sluice gate and pump station, with straight piers for the cleaning machine bridge – Calculation and effect of the flow pattern improvement in the forebay under Scheme Two:

[0051] A cleaning machine bridge is installed at the front end of the downstream guide wall of the gate station and pump station. The cleaning machine bridge uses 5 rows of evenly distributed straight piers for flow guidance within the two guide walls, as shown in the following layout scheme. Figure 5 As shown, the length of the guide wall reaches 50m.

[0052] For ease of comparison, the downstream guide wall length of Scheme 1 in step A was first changed to 50m. CFD calculations were then applied to process the streamlines and velocity distribution of the forebay with a 50m guide wall and no sludge removal bridge, as shown below. Figure 6 As shown, the width of the low-velocity vortex zone on both sides accounts for about 50% of the width of the forebay. Using formula (3), it is calculated that the area ratio of the low-velocity zone on both sides of the forebay is relatively large, reaching 10.7%, and there is a mainstream zone with a large velocity in the middle of the forebay.

[0053] The calculated streamlines and velocity distribution of the forebay in Scheme 2, with a guide wall length of 50m and straight piers at the front, are as follows: Figure 7 As shown. Comparison Figure 7 and Figure 6 It can be seen that after the straight bridge piers are set at the front end of the forebay to guide the flow, the width of the low-speed vortex zone on both sides decreases from 50% of the width of the forebay to about 30%, and the area ratio of the low-speed vortex zone decreases from 10.7% to 6.9%. Except for a small low-speed vortex zone near the inner wall of the guide wall, the streamlines in other areas are basically uniform and parallel, and the flow state of the forebay and the inflow of the side unit inlet channel are significantly improved.

[0054] D. A sluice gate combined with the downstream guide wall of the pumping station is used to install a debris removal machine bridge, with the preferred "eight"-shaped piers for the bridge – Method for determining Scheme 3 and its effect on improving flow regime:

[0055] Option 2 involves installing a straight-line pier cleaning machine bridge at the front end of the two guide walls downstream of the pumping station. Small low-velocity zones still exist near the guide walls on both sides of the forebay. Considering the cleaning machine bridge has five piers, with the middle pier remaining in a straight line, six different combinations of outward tilting angles are used for the two side piers and the two secondary side piers. Together with Options 1 and 2, there are a total of eight options, as shown in Table 1. The arrows in the rightmost column of the table indicate the direction of the incoming flow. The eight options are arranged in ascending order of the overall pier deflection angle.

[0056] Table 1. Bridge pier schemes for different cleaning machine bridges

[0057]

[0058]

[0059] E. For the downstream flow field calculation domain of the pump station in Scheme 3 (1) to Scheme 3 (6) of Table 1, CFD calculations were performed using the method in step A. The calculation results were post-processed to obtain the velocity and streamline distribution in the forebay between the two guide walls. The proportion of the area where the velocity is less than the sediment stabilization velocity was calculated. The flow direction before the inlet of the water pump was observed. The proportion of the low-velocity zone in the forebay of the pump station was calculated for a total of 8 schemes, including Scheme 1 in step A and Scheme 2 in step C. Figure 8 As shown, the area ratio of the low-velocity vortex zone in the forebay of Scheme 1 without a cleaning machine bridge reaches 10.7%; the area ratio of the low-velocity vortex zone in the forebay of Scheme 2 with straight piers is 6.9%, which is a decrease; while the smallest proportion of the low-velocity zone is in Scheme 3 (6), where the outermost and second outermost piers have an angle of 10°. Its downstream streamlines and velocity distribution are as follows. Figure 9As shown, the area ratio of the low-speed zone is only 0.4%, which is less than 1%, which basically eliminates the low-speed zone and siltation in the forebay and corrects the flow deviation phenomenon of the side unit inlet. Scheme 3 (6) has the best forebay flow. This sludge cleaning machine bridge pier arrangement scheme is the preferred scheme and is recommended for the project.

[0060] This invention improves the flow pattern in the forebay by setting up a cleaning machine bridge at the front end of the forebay in conjunction with the gate station and the pump station, and adopting the preferred "eight"-shaped bridge piers. This prevents the flow from converging, adjusts the axial direction of the water flow and makes the flow velocity uniform, and eliminates the large-area vortex low-speed zone on both sides of the forebay and the flow deviation in the inlet channel. This achieves the purpose of improving the flow pattern in the forebay, avoiding siltation, and improving the energy efficiency of the pump station.

Claims

1. A method for improving the inflow pattern of a combined sluice gate and pumping station by using the piers of a bridge with a cleaning machine to guide the flow, characterized in that, Includes the following steps: A. Propose Option 1: A guide wall is only installed downstream of the gate station combined with the pump station; perform CFD calculations and analysis on the forebay flow of Option 1: The stationary velocity of sediment is the critical flow velocity at which sediment in a water flow changes from motion to stillness. Its calculation formula is as follows: （1） In the formula: U s The stationary velocity of the sediment flow is expressed in m / s. ρ s The density of the sediment is expressed in kg / m³. ρ The density of water is kg / m³. g The acceleration due to gravity, m / s² 2 ; d The median particle size of suspended sediment is given in meters. The initiation velocity of sediment is the critical flow velocity at which sediment on the riverbed transitions from rest to motion under the influence of water flow. Its calculation formula is as follows: （2） In the formula: U e The initial velocity of the sediment flow is in m / s; h The average water depth is in meters (m). ρ s The density of the sediment is expressed in kg / m³. ρ The density of water is kg / m³. g The acceleration due to gravity, m / s² 2 ; d The median particle size of suspended sediment; m; The inlet section is a straight section of the river channel 5-8 times the water depth downstream of the sluice gate, and the outlet section is a straight section of the inlet channel for all operating units of the pumping station. The computational domain also includes an air domain 2 m above the water surface. The computational domain is divided into unstructured grids, and the grids are refined at the inlet, outlet and water surface of the computational domain. The number of grids satisfies the independence verification. The computational domain inlet and outlet are given a given mass flow rate, and the solid wall boundary is set as a no-slip wall. The calculation model considers the influence of gravity and performs CFD calculations on the water flow in the downstream calculation domain of the pumping station. The water surface is captured using the VOF method. The calculation results are post-processed to obtain the flow velocity and streamline distribution of the calculation domain, including the forebay of the pumping station. The flow regime in the forebay is observed. Formula (1) is used to determine the location and size of the siltation area in the forebay. Formula (2) is used to determine the location and size of the siltation area in the forebay that cannot be flushed away. The severity of siltation in the forebay is expressed as the percentage of the siltation area to the area of ​​the forebay. Formula (3) is used to calculate the proportion of the low-velocity siltation area in the forebay. （3） In the formula: The proportion of the low-velocity zone in the forebay where the flow velocity is lower than the sediment stagnant flow velocity; A l The area of ​​the low-velocity zone of the forebay inside the guide wall, in m 2 ; A t The total area of ​​the forebay inside the guide wall is m. 2 ; B. The inlet cleaning bridge of the gate station combined with the pump station is located at the front end of the downstream guide wall: A cleaning machine bridge is installed between the heads of the two guide walls in the forebay of the pumping station. A trash rack and a cleaning machine are installed to prevent dirt in the water from entering the pump during pumping and to remove it in time, so as to avoid affecting the flood discharge of the control gate. At the same time, the bridge piers of the cleaning machine bridge are used to guide the flow, adjust the axial direction of the water flow and make the flow velocity uniform, and improve the flow state of the forebay. C. Option 2: A cleaning machine bridge is installed at the front end of the downstream guide wall of the gate station and the pump station, and the cleaning machine bridge adopts straight piers; A series of piers are installed at the front end of the guide wall, with the piers aligned with the main flow direction and parallel to the guide wall. Using the method in step A, CFD calculations were performed on the downstream flow calculation domain of the pumping station. The calculation results were then post-processed to obtain the streamlines and velocity distribution in the forebay between the two guide walls. The proportion of the area where the velocity is less than the velocity of the sediment stop flow was calculated, and the flow direction before the inlet of the pump was observed. D. Option 3: A cleaning machine bridge is installed at the front end of the downstream guide wall of the sluice gate station and the pump station. The cleaning machine bridge adopts an "eight"-shaped pier. Using "eight" shaped piers, the water flow is directed to both sides of the forebay, adjusting the axial direction and uniform flow velocity of the forebay water flow, eliminating low-speed vortex zones, and improving the flow pattern of the forebay. Determine the deflection angle of the "eight"-shaped symmetrical piers: the middle pier located on the center line of the forebay does not deflect; set multiple sets of symmetrical piers with deflection angles of 5°, 10° and 15° respectively, and apply the method of step A to each set of pier deflection schemes in order of increasing total deflection angle. Perform CFD calculation on the downstream water flow field calculation domain of the pump station, and perform post-processing on the calculation results to obtain the streamlines and velocity distribution in the forebay between the two guide walls. Calculate the proportion of the area of ​​the region in the forebay where the velocity is less than the sediment stop velocity according to formula (3), observe the flow direction before the inlet of the water pump, and determine the range of the optimal deflection angle of each set of symmetrical piers with the goal of reducing the area of ​​the low-velocity vortex region in the forebay according to the influence law of the pier deflection angle on the inlet flow direction and the area of ​​the low-velocity region in the forebay. Further refine the pier deflection angle until the area of ​​the region in the forebay where the velocity is less than the sediment stop velocity accounts for less than 1% of the area of ​​the forebay. E. Comparing multiple options to determine the final optimal solution: Comparing the proportions of the low-velocity zone in the forebay among Schemes 1, 2, and 3, the bridge pier arrangement scheme with a low-velocity zone area ratio of less than 1% and a basic elimination of flow deviation in the side unit inlet channels was selected as the preferred scheme.

2. The method for improving the inflow pattern of a combined sluice gate and pumping station by using a bridge pier for flow diversion according to claim 1, characterized in that, The bridge piers of the cleaning machine bridge mentioned in step B are pier-wall type piers to ensure the flow guiding effect; the head and tail of the piers are streamlined to reduce flow resistance; the main body of the piers is rectangular in plan; multiple piers between the two guide walls are symmetrically arranged along the longitudinal centerline of the forebay to ensure flow symmetry.

3. The method for improving the inflow pattern of a combined sluice gate and pumping station by using a bridge pier for flow diversion according to claim 1, characterized in that, The straight piers mentioned in step C are piers symmetrically distributed about the longitudinal centerline of the forebay. The figure-eight shaped piers mentioned in step D are based on the horizontal longitudinal centerline of the forebay. The straight piers mentioned in step C are deflected outward by a certain angle around the vertical centerline of the piers in the direction of water flow. The two symmetrical piers on both sides are deflected at the same angle and in opposite directions. Looking down from the direction of the incoming flow, the pier on the left side of the longitudinal centerline of the forebay is deflected clockwise, and the pier on the right side is deflected counterclockwise. The symmetrical piers are distributed in a figure-eight shape.

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