Low-water-head curve hub and flow state improvement method thereof

Abstract

The invention relates to the field of water conservancy projects, in particular to a low-water-head curve hub and a flow state improvement method thereof, and the improvement method comprises the steps: S1, building a physical model of the hub; s2, a typical working condition is selected for hydraulic characteristic verification; s3, a flow guide wall is arranged on a first bank, and the first bank is close to a backflow vortex rolling area formed by water flow bias flow; and a flaring pier structure is arranged at the tail end of the gate pier, so that the risk that water on the surface layer of the nappe impacts a gate trunnion is reduced. According to the flow state improving method for the low-water-head curve hub, the flow guide wall is arranged on the first bank, the first bank is close to a backflow vortex rolling area formed by water flow bias, the bias flow condition on a dam can be remarkably improved, the water flow is adjusted to be smooth, and the flow state is improved; by prolonging the length of the straight section of the weir crest and arranging the flaring pier structure at the tail end of the gate pier, through the synergistic effect of the weir crest and the flaring pier structure, the risk that water on the surface layer of the nappe impacts the gate trunnion can be remarkably reduced, and safe operation of the hub flood discharge gate is ensured.

Description

Technical Field

[0001] The invention relates to the field of water conservancy projects, and in particular to a low-head bend hub and a flow pattern improvement method thereof. Background Art

[0002] A low-head bend hub refers to a water conservancy hub with a low head (usually less than 30 meters) and is arranged using the curvature of the river. A low-head bend hub can make full use of the natural curvature of the river and achieve effective use of water resources by rationally arranging water intake and sediment discharge buildings.

[0003] However, if there is a large flood discharge in a low-head bend hub, there is a risk of flow problems on the dam and splashes on the surface of the water tongue impacting the gate hinges. Therefore, it is necessary to improve the flow state of the low-head bend hub in a targeted manner. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide a low-head bend hub and a method for improving the flow pattern thereof.

[0005] In a first aspect, the present invention provides a method for improving the flow pattern of a low-head bend hub, comprising:

[0006] S1: Build a physical model of the hub;

[0007] S2: Select typical working conditions to verify hydraulic characteristics;

[0008] S3: A diversion wall is set on the first bank, which is close to the backflow vortex area formed by the water deviation; the length of the straight section of the weir top is extended and a wide tail pier structure is set at the end of the gate pier to reduce the risk of water splashes on the surface of the water tongue impacting the gate hinge.

[0009] Preferably, the lengthening of the straight section of the weir crest and the structural form of the wide tail pier are determined by numerical simulation and physical simulation, including:

[0010] S31: Establish a mathematical model of a single hole of the flood discharge gate, determine the boundary conditions of the mathematical model and the initial water flow conditions, and perform numerical simulation calculations;

[0011] S32: Change the length of the weir crest and / or the wide tail pier structure of the flood discharge gate, and perform numerical simulation calculations respectively;

[0012] S33: according to the calculation result of S32, the first risk value k1 of the impact hinge is used as a judgment condition to determine the optimal range of the weir crest extension length and / or the wide tail pier structure;

[0013] S34: Establish a physical model of a single hole of the flood discharge gate, conduct physical model tests on the schemes within the optimal range of the weir crest extension length and / or the wide tail pier structure determined in S33, and determine the optimal scheme for the weir crest extension length and / or the wide tail pier structure using the second risk value k2 of the impact support hinge as a judgment condition.

[0014] Preferably, in S33, the first risk value k1 of impacting the support hinge is expressed as follows:

[0015] k1 = f (water jump head position, jump head water depth, maximum bottom flow velocity of the lock chamber, discharge flow, lock chamber water surface line);

[0016] Where f is a function.

[0017] Preferably, in S33, the first risk value k1 of impacting the support hinge is expressed as follows:

[0018] k1 = n1f1 (water jump head position) + n2f2 (jump head water depth) + n3f3 (maximum bottom flow velocity of the lock chamber)

[0019] +n4f4(discharge flow)+n5f5(water surface line of lock chamber);

[0020] In the formula, f1, f2, f3, f4, and f5 are functions respectively, n1, n2, n3, n4, and n5 are coefficients respectively, and n1+n2+n3+n4+n5=1.

[0021] Preferably, in S33, n1≥n2>n3≥n4≥n5.

[0022] Preferably, in S34, the expression of the second risk value k2 of impacting the support hinge is as follows:

[0023] k2=m1g1(water jump head position)+m2g2(lock chamber water surface line)+m3g3(weir surface pressure)

[0024] Wherein, g1, g2, g3 are functions, m1, m2, m3 are coefficients, and m1+m2+m3=1.

[0025] Preferably, in S34, m1≥m2≥m3.

[0026] Preferably, the structural parameters of the wide tail pier include: tail pier type, opening width before contraction, pier tail angle, contraction ratio, outlet width, contraction section length, and pier top elevation.

[0027] Preferably, the guide wall in S3 is an eight-shaped guide wall.

[0028] Preferably, the step S3 further comprises expanding the slope line of the first bank.

[0029] Preferably, the typical operating conditions in S1 include: verification conditions, design conditions and energy dissipation and anti-collision conditions.

[0030] In a second aspect, the present invention provides a low-head bend hub, which is designed by any of the flow pattern improvement methods for a low-head bend hub.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The present invention provides a method for improving the flow pattern of a low-head bend hub. By setting a guide wall on the first bank, the first bank is close to the backflow vortex area formed by the deviation of water flow, which can significantly improve the deviation situation on the dam, adjust the water flow, and improve the flow pattern.

[0033] 2. The present invention provides a method for improving the flow pattern of a low-head curved hub. By extending the length of the straight section of the weir top and setting a wide tail pier structure at the end of the gate pier, the synergistic effect of the two can significantly reduce the risk of water splashes on the surface of the water tongue impacting the gate hinge, thereby ensuring the safe operation of the hub flood discharge gate. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the floor plan of the discharge structure.

[0035] Figure 2 This is the longitudinal section of the flood discharge gate.

[0036] Figure 3 This is a schematic diagram showing the risk of water splashing on the surface of the water tongue impacting the gate hinges.

[0037] Figure 4 This is a schematic diagram of the scope of the hydraulic physical model.

[0038] Figure 5 This is the overall layout diagram of the hydraulic physical model.

[0039] Figure 6 This is a schematic diagram of adding an eight-shaped diversion wall.

[0040] Figure 7 To verify the flow state on the dam under working conditions.

[0041] Figure 8 This is a schematic diagram of the outward expansion of the right bank slope on the dam.

[0042] Fig. 9 Schematic diagram of the mathematical model of a single hole of a flood discharge gate.

[0043] Fig.10 This is the boundary condition diagram of the mathematical model of the flood discharge gate.

[0044] Fig.11 This is the cross-sectional layout of the wide crest weir of the flood discharge gate.

[0045] Fig.12 Schematic diagram of the flow field in the flood discharge gate chamber.

[0046] Fig.13 This is the water surface line along the weir crest extension plan.

[0047] Fig.14 This is a schematic diagram of the structural parameters of the wide tail pier.

[0048] Fig.15 This is the plan layout of the wide tail pier.

[0049] Fig.16 This is a schematic diagram of the flow field in the lock chamber of the wide tail pier scheme.

[0050] Fig.17 This is the water surface line diagram along the wide tail pier scheme.

[0051] Fig.18 Recommended wide tail pier body parameter diagram for numerical simulation.

[0052] Fig.19 The body parameter diagram of the weir crest extension scheme recommended for numerical simulation.

[0053] Fig. 20 This is a comparison chart of the hydraulic jump positions in the lock chamber.

[0054] Fig.21 This is a comparison chart of the water surface line in the lock chamber.

[0055] Fig. 22 This is a comparison chart of the pressure on the lock chamber weir surface. DETAILED DESCRIPTION

[0056] The present invention is further described in detail below in conjunction with specific embodiments. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

[0057] Unless otherwise specified, in the description of the specific embodiments of the present invention, the terms indicating the orientation or position relationship such as "up", "down", "left", "right", "center", "inside", "outside", etc. are all based on the expression of the orientation or position relationship shown in the drawings, or are the orientation or position relationship when the invented product / equipment / device is usually used. These terms of orientation or position relationship are only for the convenience of describing the scheme of the present invention or simplifying the description in the specific embodiments, so as to facilitate the technicians to quickly understand the scheme, and do not indicate or imply that a specific device / component / element must have a specific orientation, or be constructed and operated in a specific position relationship, and therefore cannot be understood as a limitation on the present invention.

[0058] In addition, if the terms "horizontal", "vertical", "overhanging", "parallel" and the like appear, it does not mean that the corresponding devices / components / elements are required to be absolutely horizontal or vertical or overhanging or parallel, but may be slightly tilted or have deviations. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but may be slightly tilted. Alternatively, it can be simplified to mean that the corresponding devices / components / elements are set in directions such as "horizontal", "vertical", "overhanging", "parallel", etc., and can have an error / deviation of ±10% relative to the corresponding direction setting, more preferably an error / deviation within ±8%, more preferably an error / deviation within ±6%, more preferably an error / deviation within ±5%, and more preferably an error / deviation within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its role in the scheme of the present invention.

[0059] In addition, the expressions “first”, “second”, “third”, etc., which appear in the terms, are merely used to distinguish the description of the same or similar components and should not be understood as emphasizing or implying the relative importance of specific components.

[0060] In addition, in the description of the embodiments of the present invention, "several", "plurality" and "a number" represent at least 2. It can be any number such as 2, 3, 4, 5, 6, 7, 8, 9, and even more than 9.

[0061] In addition, in the description of the technical solution of the present invention, unless otherwise clearly specified / defined / restricted, the terms "set", "install", "connect", "connected", "provided with", "laid", and "arranged" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection, and can be welding, riveting, bolting, threading, and other commonly used connection means in the field. This connection can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection, or an indirect connection through an intermediate medium, and it can be the internal connection of two elements.

[0062] Example 1

[0063] The main layout of the water discharge structure of a hub is 7 flood discharge gates and 1 bottom discharge hole. The dam is 122m long and the dam top elevation is 17.50m. The plan layout and longitudinal section of the water discharge structure are shown in Figure 1-2 shown.

[0064] The 7-hole flood discharge gate is arranged in the main river channel, with a single hole net width of 13.0m and a total front width of 116.0m. The gate pier is split, with the left pier thickness of 2.0m, the middle pier thickness of 3.5m, and the right pier thickness of 2.0m. The width of a single hole is 16.50m. The flood discharge gate top elevation is 17.50m, the weir top elevation is 1.00m, and the gate chamber length along the water flow direction is 35.0m. From upstream to downstream, a flat inspection door and an arc-shaped working door are set in sequence. The inspection door is opened and closed by a mobile gantry crane on the dam top, and the working door is opened and closed by a hydraulic hoist. A 4.8m wide traffic bridge is set on the upstream side of the gate top, and the traffic bridge top elevation is 17.50m. Two gate top gantry track beams are arranged next to the traffic bridge, and oil pipe cable box beams are arranged on the downstream side. The flood discharge gate weir type adopts a wide top weir, and the weir top elevation is 1.00m. Behind the flood discharge gate, it is connected to the seafloor through a 1:4 slope. The seafloor is 100m long and a riprap anti-scour trough is set at the end.

[0065] The designed operating head range of the hub power station is 4.0m to 10.4m. The hub is a low-head riverbed hub with a large flood discharge and a large flooding depth below the gate.

[0066] In order to solve the above problems, a method for improving the flow pattern of low-head bend hub is proposed, including:

[0067] S1: Build a physical model of the hub.

[0068] According to the topographic data of the hub river section, and considering the similarity of the flow conditions of the model inlet and outlet, the flow pattern in the test section is guaranteed not to be affected. The research scope of the physical model is 510m upstream of the dam site to 650m downstream of the dam site, and the length of the simulated river section is about 1.16km. Figure 4 .

[0069] The model is supplied with water by a water supply system, and a flat water section and a water stabilization gate are set up upstream to ensure a stable water flow in the reservoir area. The reservoir area and the downstream river channel are simulated according to the actual terrain.

[0070] The terrain modeling adopts the cross-section method. The model cross-section is scaled down according to the measured riverbed terrain in plane and vertical scales. The model cross-section is made of five layers of boards and is set up by the arranged leading control. The cross-section elevation control error is less than ±1.0mm, the plane control error is less than ±1.0cm, and the terrain surface is plastered with cement mortar. The flood discharge gate, bottom hole, power station and other flow structures and the downstream sea section are made of plexiglass to facilitate flow field observation and parameter measurement.

[0071] The simulated river section is entirely lined with concrete, the prototype roughness is 0.012-0.014, the model roughness is required to be 0.006-0.008, cement mortar plastering and plexiglass can meet the roughness requirements. Figure 5 shown.

[0072] The main measuring and controlling instruments and equipment for the model test are described as follows:

[0073] Flow rate: Siemens electromagnetic flowmeter is used for control and measurement.

[0074] Tailgate water level: controlled and adjusted by a flap-type tailgate with fine-tuning function.

[0075] Water level along the route: measured using a water level probe.

[0076] Time-averaged pressure: measured using a pressure gauge.

[0077] Pulsating pressure: measured by a resistive pulsating pressure sensor.

[0078] Flow velocity: measured using a new Norwegian-made acoustic Doppler three-dimensional point flow meter and a propeller flow meter.

[0079] S2: Select typical working conditions to verify hydraulic characteristics.

[0080] Taking into account the flood control conditions of the hub and the energy dissipation and anti-scouring control conditions of the downstream sea floodplain and riverbed, three typical characteristic water levels of verification (P = 0.1%), design (P = 1%), and energy dissipation and anti-scouring (P = 2%) were selected for testing, as shown in Table 1. The flow pattern, water surface line along the way, bottom flow velocity along the way, time-averaged pressure of the bottom plate of the flood discharge gate, and pulsating pressure of the bottom plate of the downstream sea floodplain section were tested at various flow levels. The water level boundary control positions above and below the model dam are 400m above the dam and 600m below the dam, respectively, and the water level is controlled according to Table 1.

[0081] Table 1 Flood discharge gate test conditions

[0082]

[0083] The test results show that:

[0084] Affected by the upstream bend, the water flow on the dam is biased to the right bank. Under the verification and design conditions, there is a strong backflow vortex area near the inlet of the right flood discharge gate, and the flow state is relatively bad. The flooding degree of the water flow below the dam is relatively large. Under the verification condition, the water jump occurs in the steep slope section of the gate chamber, and the jump head is close to the gate hinge. The water splash on the surface of the water tongue has the risk of impacting the gate hinge, which may be detrimental to the stability of the hinge structure. Figure 3 shown.

[0085] S3: In order to improve the flow pattern on the dam, an optimization design was carried out, including:

[0086] (1) A guide wall is set on the first bank, and the first bank is close to the backflow vortex area formed by the water flow deviation to adjust the water flow and improve the flow state. Further preferably, the guide wall is an eight-shaped guide wall. In this embodiment, a guide wall (with a top elevation of 12.50m) is set on the right bank. Figure 6 shown.

[0087] After adding the figure-eight diversion wall, the water flow connection is smoother and the flow pattern of the incoming flow on the dam is improved. Figure 7 shown.

[0088] In a preferred embodiment, the S3 further includes expanding the slope line of the first bank, such as Figure 8 As shown in the figure. The outward expansion of the right bank slope and the addition of a diversion wall on the right bank can effectively adjust the water flow on the dam and reduce the degree of mainstream deviation. The waterlogging phenomenon on the right side of the flood gate inlet was significantly reduced. Under the verification and design conditions, the scope of the backflow vortex area on the right bank of the dam was significantly reduced, and the cross-flow situation of the river was significantly improved.

[0089] (2) Extend the length of the straight section of the weir crest and set a wide tail pier structure at the end of the gate pier to reduce the risk of water splashes on the surface of the water tongue impacting the gate support hinge.

[0090] The lengthening of the straight section of the weir crest and the structural form of the wide tail pier are determined by numerical simulation and physical simulation, including:

[0091] S31: Establish a single-hole mathematical model of the flood discharge gate, determine the boundary conditions and initial water flow conditions of the mathematical model, and perform numerical simulation calculations.

[0092] The mathematical model of a single hole of a flood discharge gate is as follows Fig. 9 The model study range is from 10m above the dam to 120m below the dam. The upstream boundary uses the water level boundary and the water level is set to 15.17m. The downstream boundary uses the water level boundary and the water level is set to 11.74m. The mathematical model boundary conditions and initial water flow conditions are set in Fig.10 .

[0093] S32: Change the length of the weir crest and / or the wide tail pier structure of the spillway, and perform numerical simulation calculations respectively to study the law of hydraulic jump changes and quickly grasp the improvement effect of the optimization measures.

[0094] When changing the length of the flood discharge gate weir crest, the variation range of the flood discharge gate weir crest length can be 0.5m-10m, that is, the flood discharge gate weir crest length can be increased by 0.5m to about 10m, and mathematical simulation calculations are performed in sequence.

[0095] Furthermore, when changing the length of the flood gate crest, the flood gate crest length can be linearly changed or nonlinearly changed, and usually the change increment of the flood gate crest length is 0.1m-0.5m. For example, taking 0.5m as a change increment, the increase values ​​of the flood gate crest length are: 0.5m, 1m, 1.5m, 2m... It can also be a nonlinear change, for example, the increase values ​​of the flood gate crest length are: 1m, 2m and 5m, etc.

[0096] Considering the lengthening of the straight section of the weir crest (elevation 1.00m), the cross-section of the wide crest weir of the flood discharge gate is arranged as follows: Fig.11 The calculation conditions and statistical results are shown in Table 1. The longitudinal flow field results under each scheme are shown in Fig.12 As shown, the water surface line along the way is as follows Fig.13 According to the calculation results, the flow rate will be slightly reduced if the length of the straight section of the weir top is lengthened, and the flow rate will be reduced by about 0.5% if the length is increased by 5m.

[0097] When lengthened by 1m and 2m, the water jump head moves down by about 1.5m and 3.0m respectively, and the water depth of the contraction section does not change much; when lengthened by 5m, although the water jump head moves down, the water depth of the contraction section increases significantly. According to the flow field distribution diagram, the risk of impacting the support hinge is further increased.

[0098] Table 2 Calculation conditions and statistical results of the weir crest extension scheme

[0099]

[0100] When the wide tail pier structure form is changed, the wide tail pier structure parameters include: tail pier type, opening width before contraction, pier tail angle, contraction ratio, outlet width, contraction section length, and pier top elevation. The wide tail pier can refer to the wide tail pier body parameters of some existing low head projects in Table 3. The wide tail pier body parameters are shown in Table 3. Fig.14 .

[0101] Table 3 Body parameters of wide tail piers in typical projects

[0102]

[0103] In the table, the contraction ratio ε = B' / B; the initial inflection point position parameter ξ x =X / H d .

[0104] Based on the layout characteristics of the hub flood discharge gate and referring to relevant engineering experience, the wide tail pier body shape is designed. Two wide tail pier inflection points are initially selected: (1) According to the actual layout of the project, in order to ensure the smooth lateral transition of the water flow, the wide tail pier inflection point is selected at the original gate wall width change point, 18.33m away from the end of the gate pier; (2) According to engineering experience, the wide tail pier inflection point is selected at 8m away from the end of the gate pier, the contraction ratio is selected as 0.5, and the corresponding pier tail inflection angle is 20°. The plan layout of the two wide tail pier body shapes is shown in the figure. Fig.15 shown.

[0105] The calculation conditions and statistical results are shown in Table 4. The traditional straight-wall wide tail pier is suitable for flood discharge in the case of high tailwater and large single width. When the tailwater depth is small or the flood discharge is small, water concentration is likely to occur, which will cause the impact pressure of the downstream sea section to increase sharply. In order to increase the applicability of the wide tail pier structure to the downstream discharge flow, the X-type wide tail pier structure is also studied.

[0106] The longitudinal flow field results under various schemes are as follows Fig.16 As shown, the water surface line along the way is as follows Fig.17 shown.

[0107] Table 4 Calculation conditions and statistical results of the wide tail pier scheme

[0108]

[0109] S33: According to the calculation result of S32, the first risk value k1 of the impact support hinge is used as a judgment condition to determine the optimal range of the weir crest extension length and / or the wide tail pier structure.

[0110] In S33, the expression of the first risk value k1 of impacting the support hinge can be as follows:

[0111] k1 = f (water jump head position, jump head water depth, maximum bottom flow velocity of the lock chamber, discharge flow, lock chamber water surface line);

[0112] Where f is a function.

[0113] When calculating the first risk value k1 of impacting the support hinge, it is necessary to first identify the influencing factors that affect the risk of impacting the support hinge. Through research and analysis, it is determined that the first risk value k1 of impacting the support hinge is highly correlated with the water jump head position, jump head water depth, maximum bottom flow velocity of the lock chamber, discharge flow, and lock chamber water surface line, that is, the water jump head position, jump head water depth, maximum bottom flow velocity of the lock chamber, discharge flow, and lock chamber water surface line are influencing factors.

[0114] Furthermore, in S3, the expression of the first risk value k1 of impacting the support hinge can be as follows:

[0115] k1 = n1f1 (water jump head position) + n2f2 (jump head water depth) + n3f3 (maximum bottom flow velocity of the lock chamber)

[0116] +n4f4(discharge flow)+n5f5(water surface line of lock chamber);

[0117] In the formula, f1, f2, f3, f4, and f5 are functions, n1, n2, n3, n4, and n5 are coefficients, and n1+n2+n3+n4+n5=1. n1, n2, n3, n4, and n5 represent the importance of different influencing factors. The values ​​of n1, n2, n3, n4, and n5 can be different, and the larger the value, the more important it is.

[0118] In the calculation of the impact hinge risk, the most important influencing factor is identified and assigned the largest coefficient. By setting different importance levels, the first risk value k1 of the impact hinge can be obtained more accurately.

[0119] Furthermore, n1≥n2>n3≥n4≥n5. That is, the influence and importance of the water jump head position and the water depth of the jump head are usually greater than the influence and importance of the maximum bottom flow velocity, discharge flow and water surface line of the lock chamber.

[0120] For example, for the extension of the weir crest, based on the numerical simulation calculation results of extensions of 1m, 2m and 5m, it is recommended that the schemes of extension by 1m and 2m are the better options, that is, extension of 1-2m is the better range for extending the weir crest.

[0121] According to the settlement results, adding a wide tail pier structure has basically no effect on the flow rate. The recommended layouts of the three wide tail pier structures are as follows: Fig.18 shown.

[0122] When selecting a better solution, the present invention can consider the two forms of the weir top extension solution and the wide tail pier structure separately, that is, only the weir top extension structure is set in one numerical simulation model, and only the wide tail pier structure is set in another numerical simulation model. In this way, the influence of the weir top extension length and the wide tail pier structure parameters can be analyzed respectively.

[0123] However, it is preferred to consider both the weir crest extension scheme and the wide tail pier structure when selecting a better scheme, that is, the weir crest extension structure and the wide tail pier structure are set up at the same time in a numerical simulation model, and various combinations of the two forms are considered in the simulation analysis, and the possibility of mutual influence between the two structural forms is considered. Therefore, a better scheme can be selected when the two forms coexist and work together, making the selected scheme more realistic and reliable.

[0124] S34: Establish a physical model of a single hole of the flood discharge gate, conduct physical model tests on the schemes within the optimal range of the weir crest extension length and / or the wide tail pier structure determined in S33, and determine the optimal scheme for the weir crest extension length and / or the wide tail pier structure using the second risk value k2 of the impact support hinge as a judgment condition.

[0125] For example, for the lengthening of the weir crest, based on the preliminary optimization results of the numerical model, the physical model was tested for the recommended solutions (1m and 2m lengthening of the weir crest). Fig.19 shown.

[0126] The water jump head position after the weir crest was lengthened, the water surface line of the lock chamber and the pressure distribution on the weir surface were tested under the specified working conditions. The specific results are as follows.

[0127] (1) Water jump first position

[0128] The hydraulic jump of the lock chamber under the original design and the weir crest extension (1m, 2m) scheme is shown in Figure 2. Fig. 20It can be seen that the position of the water jump is significantly lowered after the weir crest is lengthened. When the weir crest is lengthened by 1m, the water jump is at 0+035.56m below the dam, which is 1m lower than the original design. When the weir crest is lengthened by 2m, the water jump is at 0+037.46m below the dam, which is 2.9m lower than the original design. Under the weir crest lengthening scheme, the risk of water tongue impacting the gate hinge is eliminated.

[0129] (2) Water surface line and pressure

[0130] The water surface line of the lock chamber and the pressure distribution of the weir surface (along the center line of No. 4 flood discharge gate) under the original design scheme and the weir top extension (1m, 2m) scheme are shown in Fig.21 , Fig. 22 Corresponding to the flow pattern diagram, under the weir crest extension scheme, the water surface line at the weir crest is slightly raised, and the water jump position moves down. At 100m below the dam, the water surface lines of the original design scheme and the weir crest extension scheme are basically consistent. The weir surface pressure is positive pressure.

[0131] Specifically, in S4, the expression of the second risk value k2 of impacting the support hinge is as follows:

[0132] k2 = g (water jump head position, lock chamber water surface line, weir surface pressure);

[0133] Where g is a function.

[0134] When calculating the second risk value k2 of impacting the hinge, the influencing factors that affect the risk of impacting the hinge must be identified first. The numerical simulation results show that the water jump position and the water surface line of the lock chamber have a greater impact on the risk of impacting the hinge. Therefore, the water jump position and the water surface line of the lock chamber are selected as the influencing factors of the second risk value k2 of impacting the hinge, and the weir surface pressure is added as an influencing factor. It can be seen that the selection of influencing factors that affect the risk of impacting the hinge can be further optimized through the numerical simulation results. For example, the water jump position and the water surface line of the lock chamber are selected as the influencing factors of the second risk value k2 of impacting the hinge, while the water depth of the lock head, the maximum bottom flow velocity of the lock chamber, and the discharge flow are no longer used as influencing factors, thereby further optimizing the calculation expression of the second risk value k2, so as to obtain more accurate risk assessment results.

[0135] In S4, the expression of the second risk value k2 of impacting the support hinge can be as follows:

[0136] k2=m1g1(water jump head position)+m2g2(lock chamber water surface line)+m3g3(weir surface pressure)

[0137] In the formula, g1, g2, g3 are functions, m1, m2, m3 are coefficients, and m1+m2+m3=1. The values ​​of m1, m2, m3 can be different, and the larger the value, the more important it is.

[0138] In the calculation of the risk of impacting the support hinge, the most important influencing factor is identified and assigned the largest coefficient. By setting different importance levels, the second risk value k2 of the impacting the support hinge can be obtained more accurately.

[0139] Furthermore, m1≥m2≥m3. That is, usually the influence and importance of the water jump head position is greater than the influence and importance of the lock chamber water surface line, and the influence and importance of the lock chamber water surface line is greater than the influence and importance of the weir surface pressure.

[0140] For example, in this embodiment, in the recommended schemes determined by numerical simulation (schemes with the weir top extended by 1m and 2m), since the position of the water jump head in the scheme with the weir top extended by 2m is farther away from the support, and the water surface line is basically consistent with the original design scheme, the weir surface pressure is positive pressure, which further determines that extending the weir top by 2m is the optimal scheme.

[0141] The present invention provides a method for improving the flow pattern of a low-head bend hub. First, by establishing a physical model of the hub and conducting hydraulic tests, problems in the preliminary design scheme can be identified: affected by the upstream bend river flow, the water flow on the dam deviates to the right bank. Under the verification and design conditions, there is a strong backflow vortex zone near the inlet of the right flood discharge gate, and the flow pattern is relatively poor; the flooding degree of the water flow below the dam is relatively large. Under the verification conditions, the water jump occurs in the steep slope section of the gate chamber, and the jump head is close to the gate hinge. The water splash on the surface of the water tongue has the risk of impacting the gate hinge, which may be detrimental to the stability of the hinge structure. Based on this problem, the present invention has been optimized to set a guide wall on the first bank, which is close to the backflow vortex zone formed by the biased water flow, so as to smooth the water flow and improve the flow pattern; extend the length of the straight section of the weir top and set a wide tail pier structure at the end of the gate pier to reduce the risk of water splash on the surface of the water tongue impacting the gate hinge. In order to reduce the consumables and costs of the physical model and improve the efficiency of the physical model test, the present invention also effectively combines numerical simulation and physical model, specifically:

[0142] First, a mathematical model of a single hole of the flood discharge gate is established to study the law of hydraulic jump changes, so that the improvement effect of the optimization measures can be quickly grasped and the optimal solution can be preliminarily determined, thereby reducing the number of model modifications of the physical model. For example, in the weir crest lengthening solution in this embodiment, the physical model was only modified twice (the weir crest lengthening solution of 1m and 2m), reducing the consumables and costs of the physical model and improving the efficiency of the physical model test. Then, the optimal solution determined by the mathematical model is further confirmed through the physical model test, and finally the optimal solution for the weir crest length of the flood discharge gate is determined.

[0143] The present invention can preliminarily determine a better solution based on the mathematical model by combining mathematical simulation calculations and physical model tests, and further confirm the better solution determined by the mathematical model through physical model tests, and finally determine the optimal solution of the flood discharge gate crest length / wide tail weir structure, which can greatly reduce the number of model modifications of the physical model, reduce the consumables and costs of the physical model, and improve the efficiency of the physical model test. Moreover, through the dual verification of mathematical simulation calculations and physical model tests, the feasibility and accuracy of the optimization plan can be further guaranteed. The optimized flood discharge gate can effectively reduce the risk of water splashes on the surface of the water tongue impacting the gate hinge, ensure the safe operation of the hub flood discharge gate, and significantly improve the deviation of the dam, adjust the water flow, and improve the flow state.

[0144] Example 2

[0145] A low-head bend hub is designed by a flow pattern improvement method for a low-head bend hub as described in Example 1.

[0146] The flood discharge gate described in the present invention is designed using the method of Example 1. By optimizing the length of the flood discharge gate crest and adding a guide wall and a wide tail pier structure, the risk of water splashes on the surface of the water tongue impacting the gate hinge can be effectively reduced, the flow state on the dam can be improved, and the safe operation of the hub flood discharge gate can be ensured.

[0147] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the flow pattern of a low-head bend hub, characterized in that: include: S1: Build a physical model of the hub; S2: Select typical working conditions to verify hydraulic characteristics; S3: A diversion wall is set on the first bank, which is close to the backflow vortex area formed by the water deviation; the length of the straight section of the weir top is extended and a wide tail pier structure is set at the end of the gate pier to reduce the risk of water splashes on the surface of the water tongue impacting the gate hinge.

2. A method for improving the flow pattern of a low-head bend hub according to claim 1, characterized in that: The lengthening of the straight section of the weir crest and the structural form of the wide tail pier are determined by numerical simulation and physical simulation, including: S31: Establish a mathematical model of a single hole of the flood discharge gate, determine the boundary conditions of the mathematical model and the initial water flow conditions, and perform numerical simulation calculations; S32: Change the length of the weir crest and / or the wide tail pier structure of the flood discharge gate, and perform numerical simulation calculations respectively; S33: according to the calculation result of S32, the first risk value k1 of the impact hinge is used as a judgment condition to determine the optimal range of the weir crest extension length and / or the wide tail pier structure; S34: Establish a physical model of a single hole of the flood discharge gate, conduct physical model tests on the schemes within the optimal range of the weir crest extension length and / or the wide tail pier structure determined in S33, and determine the optimal scheme for the weir crest extension length and / or the wide tail pier structure using the second risk value k2 of the impact support hinge as a judgment condition.

3. A method for improving flow pattern of a low-head bend hub according to claim 2, characterized in that: In S33, the expression of the first risk value k1 of impacting the support hinge is as follows: k1 = f (water jump head position, jump head water depth, maximum bottom flow velocity of the lock chamber, discharge flow, lock chamber water surface line); Where f is a function.

4. A method for improving flow pattern of a low-head bend hub according to claim 3, characterized in that: In S33, the expression of the first risk value k1 of impacting the support hinge is as follows: k1 = n1f1 (water jump head position) + n2f2 (jump head water depth) + n3f3 (maximum bottom flow velocity of the lock chamber) +n4f4(discharge flow)+n5f5(water surface line of lock chamber); In the formula, f1, f2, f3, f4, and f5 are functions respectively, n1, n2, n3, n4, and n5 are coefficients respectively, and n1+n2+n3+n4+n5=1.

5. A method for improving flow pattern of a low-head bend hub according to claim 4, characterized in that: In S33, n1≥n2>n3≥n4≥n5.

6. A method for improving flow pattern of a low-head bend hub according to claim 4, characterized in that: In S34, the expression of the second risk value k2 of impacting the support hinge is as follows: k2=m1g1(water jump head position)+m2g2(lock chamber water surface line)+m3g3(weir surface pressure) Wherein, g1, g2, g3 are functions, m1, m2, m3 are coefficients, and m1+m2+m3=1.

7. A method for improving flow pattern of a low-head bend hub according to claim 6, characterized in that: In S34, m1≥m2≥m3.

8. The method for improving the flow pattern of a low-head bend hub according to claim 2, characterized in that: The structural parameters of the wide tail pier include: tail pier type, opening width before contraction, pier tail angle, contraction ratio, outlet width, contraction section length, and pier top elevation.

9. A method for improving flow pattern of a low-head bend hub according to claim 1, characterized in that: The guide wall in S3 is an eight-shaped guide wall.

10. The method for improving the flow pattern of a low-head bend hub according to claim 1, characterized in that: The step S3 further includes expanding the slope line of the first bank.

11. A method for improving the flow pattern of a low-head bend hub according to any one of claims 1 to 10, characterized in that: The typical working conditions in S1 include: verification working conditions, design working conditions and energy dissipation and anti-collision working conditions.

12. A low-head bend hub, characterized in that: The method is designed by a flow pattern improvement method for a low-head bend hub as described in any one of claims 1-11.

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