A low-head bend hub and its flow regime improvement method

Abstract

This invention relates to the field of hydraulic engineering, specifically to a low-head bend dam and its flow regulation improvement method. The improvement method includes: S1: establishing a physical model of the dam; S2: selecting typical operating conditions for hydraulic characteristic verification; S3: setting a guide wall on the first bank, which is close to the backflow vortex zone formed by the deflected flow; extending the length of the straight section of the weir crest and setting a wide tail pier structure at the end of the gate pier to reduce the risk of surface water splash impacting the gate hinges. This invention provides a flow regulation improvement method for a low-head bend dam. By setting a guide wall on the first bank, which is close to the backflow vortex zone formed by the deflected flow, the flow deviation situation above the dam can be significantly improved, the flow can be smoothed, and the flow regulation improved. By extending the length of the straight section of the weir crest and setting a wide tail pier structure at the end of the gate pier, the risk of surface water splash impacting the gate hinges can be significantly reduced through the synergistic effect of the two, ensuring the safe operation of the dam's spillway gate.

Description

Technical Field

[0001] This invention relates to the field of water conservancy engineering, and in particular to a low-head bend hub and a method for improving its flow regime. Background Technology

[0002] Low-head bend water conservancy projects refer to water conservancy projects with relatively low water heads (usually below 30 meters) that are arranged using the bends in the river channel. Low-head bend water conservancy projects can make full use of the natural bends in the river channel and achieve effective use of water resources through the rational arrangement of water intake, sediment removal and other structures.

[0003] However, if a low-head bend dam has a large discharge flow, it is prone to problems with the flow pattern above the dam and the risk of surface water splashes impacting the gate hinges. Therefore, it is necessary to specifically improve the flow pattern of the low-head bend dam. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-head bend hub and a method for improving its flow regime.

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

[0006] S1: Establish the physical model of the hub;

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

[0008] S3: A guide wall is set on the first bank, which is close to the backflow vortex area formed by the deflection of the water flow; the length of the straight section of the weir crest is extended and a wide tail pier structure is set at the end of the gate pier to reduce the risk of the surface water jet impacting the gate hinges.

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

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

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

[0012] S33: Based on the calculation results of S32, the optimal range of the dam crest extension length and / or wide tail pier structure form is determined using the first risk value k1 of the impact hinge as the judgment condition.

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

[0014] Preferably, in S33, the expression for the first risk value k1 of the impact support hinge is as follows:

[0015] k1 = f(position of the water jump, water depth at the jump, maximum near-bottom velocity of the gate chamber, discharge flow rate, water surface line of the gate chamber);

[0016] In the formula, f is a function.

[0017] Preferably, in step S33, the expression for the first risk value k1 of the impact support hinge is as follows:

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

[0019] +n4f4 (discharge flow) +n5f5 (water level in the gate chamber);

[0020] 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.

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

[0022] Preferably, in step S34, the expression for the second risk value k2 of the impact hinge is as follows:

[0023] k2 = m1g1 (position of the water jump head) + m2g2 (water level in the lock chamber) + m3g3 (pressure on the weir surface)

[0024] In the formula, g1, g2, and g3 are functions, m1, m2, and 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, orifice width before contraction, tail pier bend angle, contraction ratio, outlet width, contraction section length, and pier top elevation.

[0027] Preferably, the guide wall in S3 is a figure-eight guide wall.

[0028] Preferably, S3 further includes extending the slope line of the first bank outward.

[0029] Preferably, the typical operating conditions in S1 include: verification operating conditions, design operating conditions, and energy dissipation and shock protection operating conditions.

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

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. This invention provides a method for improving the flow pattern of a low-head bend hub. By setting a guide wall on the first bank, which is close to the backflow vortex zone formed by the deflection of the water flow, the flow deflection situation on the dam can be significantly improved, the water flow can be smoothed, and the flow pattern can be improved.

[0033] 2. This invention provides a method for improving the flow pattern of a low-head bend hub. By extending the length of the straight section of the weir crest and setting a wide tail pier structure at the end of the gate pier, the risk of water jet impacting the gate hinges can be significantly reduced through the synergistic effect of the two, ensuring the safe operation of the hub's flood discharge gate. Attached Figure Description

[0034] Figure 1 This is a plan view of the spillway structure.

[0035] Figure 2 This is a longitudinal section view of the floodgate.

[0036] Figure 3 This is a schematic diagram illustrating the risk of water droplets on the surface of the water jet 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 a diagram showing the overall layout of the hydraulic engineering physical model.

[0039] Figure 6 A schematic diagram for adding a figure-eight flow guide wall.

[0040] Figure 7 To verify the flow pattern above the dam under working conditions.

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

[0042] Figure 9 This is a schematic diagram of the mathematical model of a single outlet of a floodgate.

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

[0044] Figure 11 This is a cross-sectional layout diagram of the broad crest weir of the flood discharge gate.

[0045] Figure 12 This is a schematic diagram of the flow field in the floodgate chamber.

[0046] Figure 13 The water surface line along the route of the dam crest extension scheme.

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

[0048] Figure 15 This is a plan view of the wide tail pier.

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

[0050] Figure 17 This is a water surface line diagram along the route of the wide tail pier scheme.

[0051] Figure 18 Recommended shape parameter diagrams for wide-tail piers in numerical simulation.

[0052] Figure 19 The diagram shows the shape parameters of the recommended weir crest lengthening scheme for numerical simulation.

[0053] Figure 20 This is a comparison diagram of the hydraulic jump positions in the gate chamber.

[0054] Figure 21 This is a comparison diagram of the water level in the sluice chamber.

[0055] Figure 22 This is a comparison diagram of the pressure on the sluice gate weir surface. Detailed Implementation

[0056] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0057] Unless otherwise specified, the use of terms such as "upper," "lower," "left," "right," "center," "inner," and "outer" to indicate orientation or positional relationships in the description of specific embodiments of the present invention is based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationship in which the product / equipment / device is typically placed during use. These terms are merely for the purpose of facilitating the description of the present invention or simplifying the description in specific embodiments, enabling those skilled in the art to quickly understand the solution, and do not indicate or imply that a particular device / component / element must have a specific orientation, or be constructed and operated in a specific positional relationship. Therefore, they should not be construed as limitations on the present invention.

[0058] Furthermore, the use of terms such as "horizontal," "vertical," "suspended," and "parallel" does not imply that the corresponding device / component / element must be absolutely horizontal, vertical, suspended, or parallel, but rather that it can be slightly tilted or have a deviation. For example, "horizontal" merely means that its direction is more horizontal relative to "vertical," not that the structure must be completely horizontal, but that it can be slightly tilted. Alternatively, it can be simplified to mean that the corresponding device / component / element, when set in a "horizontal," "vertical," "suspended," or "parallel" direction, can have an error / deviation of ±10% relative to the corresponding direction, more preferably within ±8%, more preferably within ±6%, more preferably within ±5%, and more preferably within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its function in the present invention.

[0059] Furthermore, the use of terms such as "first," "second," and "third" in terminology is merely for distinguishing between identical or similar components and should not be interpreted as emphasizing or implying the relative importance of a particular component.

[0060] Furthermore, in the description of the embodiments of the present invention, "several", "more than", and "a number of" represent at least two. The number can be any number, such as 2, 3, 4, 5, 6, 7, 8, or 9, and can even exceed nine.

[0061] Furthermore, in the description of the technical solution of this invention, unless otherwise explicitly specified / limited / restricted, the terms "set up," "install," "connect," "link," "provided with," "laid out," and "arranged" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to common connection methods in the art, such as welding, riveting, bolting, and threaded connections. Such connections can be mechanical, electrical, or communication connections; they can be direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components.

[0062] Example 1

[0063] The spillway structure of a certain hub mainly consists of 7 floodgates and 1 bottom outlet. The dam is 122m long and the crest elevation is 17.50m. The plan layout and longitudinal section of the spillway structure are shown below. Figure 1-2 As shown.

[0064] The seven-gate spillway is located in the main channel, with a single gate having a net width of 13.0m and a total frontal width of 116.0m. It employs a segmented pier design, with the left pier being 2.0m thick, the middle pier 3.5m thick, and the right pier 2.0m thick, resulting in a single-gate span width of 16.50m. The spillway crest elevation is 17.50m, the weir crest elevation is 1.00m, and the gate chamber is 35.0m long in the direction of water flow. From upstream to downstream, a flat inspection gate and an arc-shaped working gate are sequentially installed. The inspection gate is opened and closed using a mobile gantry crane on the dam crest, while the working gate is opened and closed using a hydraulic hoist. A 4.8m wide traffic bridge is located upstream of the gate crest, with a bridge crest elevation of 17.50m. Two gantry crane track beams are located adjacent to the traffic bridge, and a cable and oil pipeline box girder is located downstream. The spillway weir is a broad-crested weir, with a crest elevation of 1.00m for all sections. After the floodgate, it connects to the sea via a 1:4 slope. The sea is 100m long and has a rock-filled anti-scour trough at the end.

[0065] The hydropower station is designed to operate within a head range of 4.0m to 10.4m. It is a low-head riverbed type hydropower station with a large flood discharge and a large downstream submersion.

[0066] To address the aforementioned issues, a flow regime improvement method for low-head bend hubs is proposed, comprising:

[0067] S1: Establish the physical model of the hub.

[0068] Based on the topographic data of the key river section and considering the requirement for similar inlet and outlet flow conditions in the model, to ensure that the flow pattern within the experimental section remains unaffected, the physical model study area is taken from 510m upstream of the dam site to 650m downstream of the dam site, simulating a river section length of approximately 1.16km. For details of the model range, please refer to [link to details]. Figure 4 .

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

[0070] The terrain model was constructed using the cross-sectional method, with the model cross-section scaled down to the measured riverbed topography according to both planar and vertical scales. The model cross-section was constructed from five layers of slabs and erected using a pre-arranged control system. The elevation control error was less than ±1.0 mm, and the planar control error was less than ±1.0 cm. The terrain surface was finished with cement mortar. The spillway, bottom outlet, power station, and other flow-through structures, as well as the downstream apron section, were constructed using processed 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, and the model roughness is required to be 0.006–0.008. Cement mortar finishing and plexiglass can meet the roughness requirements. The model layout on site is as follows. Figure 5 As shown.

[0072] The main measurement and control instruments and equipment for the model test are detailed below:

[0073] Flow rate: Siemens electromagnetic flowmeters are used for control and measurement.

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

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

[0076] Average pressure: Measured using a pressure gauge.

[0077] Pulsating pressure: Measured using a resistive pulsating pressure sensor.

[0078] Flow velocity: Measured using a new type of acoustic Doppler three-dimensional point velocity meter and propeller velocity meter made in Norway.

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

[0080] Taking into account both the flood control conditions of the dam and the energy dissipation and scour prevention conditions of the downstream apron and riverbed, three typical characteristic water levels—check (P=0.1%), design (P=1%), and energy dissipation and scour prevention (P=2%)—were selected for testing, as shown in Table 1. Flow patterns, water surface elevation along the spillway, bottom velocity along the spillway, hourly average pressure on the spillway floor, and pulsating pressure on the downstream apron floor were measured at various flow rates. The water level boundary control positions above and below the dam were 400m above and 600m below the dam, respectively, and the water levels were controlled according to Table 1.

[0081] Table 1. Test conditions of the floodgate

[0082]

[0083] The experimental results show that:

[0084] Due to the influence of the upstream bend, the water flow upstream of the dam is biased towards the right bank. Under both the verification and design conditions, a strong backflow vortex zone exists near the inlet of the right-side spillway, resulting in a relatively severe flow pattern. Downstream of the dam, the submergence is significant. Under the verification condition, the hydraulic jump occurs on the steep slope of the gate chamber, with the jump head located close to the gate hinge. The surface water jet poses a risk of impacting the gate hinge, potentially negatively affecting the stability of the hinge structure. Figure 3 As shown.

[0085] S3: To improve the flow regime above the dam, optimized design was implemented, including:

[0086] (1) A guide wall is installed on the first bank, which is close to the backflow vortex area formed by the deflected water flow, to regulate the water flow and improve the flow pattern. More preferably, the guide wall is a figure-eight guide wall. In this embodiment, a guide wall (top elevation 12.50m) is installed on the right bank. Figure 6 As shown.

[0087] After the addition of the V-shaped guide wall, the water flow connection was smoother, and the flow pattern of the incoming flow above the dam was improved. Specifically, the flow pattern above the dam under the check condition was as follows: Figure 7 As shown.

[0088] In a preferred embodiment, S3 further includes extending the slope line of the first bank outward, such as... Figure 8 As shown, the scheme of expanding the right bank slope of the dam and adding a guide wall on the right bank can effectively adjust the water flow above the dam and reduce the degree of mainstream flow deviation. The backwater phenomenon on the right side of the floodgate intake is significantly reduced. Under the verification and design conditions, the range of the backflow vortex zone on the right bank of the dam is significantly reduced, and the crossflow situation of the river channel is 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 jets impacting the gate hinges.

[0090] The extended length of the straight section of the weir crest and the structural form of the wide tail pier were determined through both numerical and physical simulations, including:

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

[0092] Mathematical model of a single spillway gate as follows Figure 9 As shown. The model's research range is from 10m upstream of the dam to 120m downstream. The upstream boundary uses a water level boundary with a water level set at 15.17m, and the downstream boundary uses a water level boundary with a water level set at 11.74m. The boundary conditions and initial flow settings for the mathematical model are shown below. Figure 10 .

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

[0094] When changing the length of the spillway weir crest, the range of variation for the spillway weir crest length can be 0.5m-10m, that is, the spillway weir crest length can be increased from 0.5m to about 10m, and mathematical simulation calculations are performed accordingly.

[0095] Furthermore, when changing the length of the spillway crest, the length can change linearly or non-linearly. Typically, the increment of the spillway crest length is 0.1m-0.5m. For example, using a 0.5m increment, the increase in the spillway crest length would be 0.5m, 1m, 1.5m, 2m, and so on. Alternatively, it can change non-linearly, for example, with increases of 1m, 2m, and 5m, etc.

[0096] Considering extending the straight section of the weir crest (elevation 1.00m), the cross-sectional layout of the broad-crested weir of the flood discharge gate is as follows: Figure 11 As shown in Table 1, the calculation conditions and statistical results are presented, and the longitudinal flow field results for each scheme are as follows. Figure 12 As shown, the water surface line along the path is as follows Figure 13 As shown. According to the settlement results, lengthening the straight section of the weir crest will slightly reduce the flow rate; an increase of 5m will reduce it by approximately 0.5%.

[0097] The hydraulic jump head was moved down by about 1.5m and 3.0m respectively when the length was increased by 1m and 2m, and the water depth at the contraction section did not change much. When the length was increased by 5m, although the hydraulic jump head was moved down, the water depth at the contraction section increased significantly, which, according to the flow field distribution diagram, increased the risk of impact on the hinge.

[0098] Table 2. Calculation conditions and statistical results for the weir crest lengthening scheme.

[0099]

[0100] When changing the structural form of the wide-tail pier, the structural parameters of the wide-tail pier include: pier type, orifice width before contraction, pier tail angle, contraction ratio, outlet width, contraction section length, and pier top elevation. The shape parameters of wide-tail piers in some existing low-head projects can be referenced in Table 3. Figure 14 .

[0101] Table 3. Body shape parameters of wide-tail piers in typical completed projects

[0102]

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

[0104] Based on the layout characteristics of the flood discharge gate of the hub and referring to relevant engineering experience, the wide-tail pier body shape was designed. Two initial turning points of the wide-tail pier were initially selected. (1) According to the actual layout of the project, in order to ensure a smooth lateral transition of the water flow, the starting point of the wide-tail pier was selected at the point where the width of the original gate wall changes, 18.33m from the end of the gate pier; (2) According to engineering experience, the starting point of the wide-tail pier was selected at 8m from the end of the gate pier, with a contraction ratio of 0.5 and a corresponding tail-end turning angle of 20°. The plan layout of the two wide-tail pier body shapes is as follows. Figure 15 As shown.

[0105] The calculation conditions and statistical results are shown in Table 4. Traditional straight-wall wide tail piers are suitable for flood discharge in situations with high tailwater depth and large unit width. However, when the tailwater depth is small or the discharge flow is low, water flow concentration is likely to occur, which will cause a sharp increase in the impact pressure of the downstream floodplain. To increase the applicability of the wide tail pier structure to the discharge flow, an X-type wide tail pier structure was also studied.

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

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

[0108]

[0109] S33: Based on the calculation results of S32, the optimal range of the dam crest extension length and / or wide tail pier structure form is determined using the first risk value k1 of the impact hinge as the judgment condition.

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

[0111] k1 = f(position of the water jump, water depth at the jump, maximum near-bottom velocity of the gate chamber, discharge flow rate, water surface line of the gate chamber);

[0112] In the formula, f is a function.

[0113] When calculating the first risk value k1 of the impact hinge, it is necessary to first identify the influencing factors affecting the impact hinge risk. Through research and analysis, it was determined that the first risk value k1 of the impact hinge is highly correlated with the position of the hydraulic jump, the depth of the jump, the maximum near-bottom velocity of the gate chamber, the discharge flow rate, and the water surface line of the gate chamber. That is, the position of the hydraulic jump, the depth of the jump, the maximum near-bottom velocity of the gate chamber, the discharge flow rate, and the water surface line of the gate chamber are the influencing factors.

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

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

[0116] +n4f4 (discharge flow) +n5f5 (water level in the gate chamber);

[0117] In the formula, f1, f2, f3, f4, and f5 are functions, and n1, n2, n3, n4, and n5 are coefficients, with 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, with larger values ​​indicating greater importance.

[0118] In the calculation of impact hinge risk, the most important influencing factors are identified and assigned the largest coefficient. By setting different levels of importance, 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 position and depth of the hydraulic jump head are generally greater than the influence and importance of the maximum bottom velocity, discharge capacity, and water surface line of the lock chamber.

[0120] For example, regarding the length of the weir crest extension, based on the numerical simulation results of extensions of 1m, 2m, and 5m, the recommended options are 1m and 2m extensions, which are the optimal range for the weir crest extension length.

[0121] According to the settlement results, the addition of wide tail pier structures has virtually no impact on the flow rate. The recommended layouts for the three wide tail pier structure types are as follows: Figure 18 As shown.

[0122] When selecting a better solution, this invention can consider the two forms of weir crest extension scheme and wide tail pier structure separately. That is, only the weir crest 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 crest extension length and the wide tail pier structure parameters can be analyzed separately.

[0123] However, it is preferable to consider both the dam crest extension scheme and the wide tail pier structure when selecting the better scheme. That is, the dam crest extension structure and the wide tail pier structure are set up simultaneously in a numerical simulation model. 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, it is possible to select the better scheme when the two forms coexist and work together, so that the selected scheme is more realistic and reliable.

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

[0125] For example, regarding the extension of the weir crest length, based on the preliminary optimization results of the numerical model, the physical model was tested against the recommended schemes (weir crest extensions of 1m and 2m). The scheme layout is as follows: Figure 19 As shown.

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

[0127] (1) Water Jump Head Position

[0128] Hydraulic jump of the gate chamber under the original design scheme and the scheme with the weir crest lengthened (1m, 2m) Figure 20It can be seen that after the weir crest was lengthened, the position of the water jump head shifted significantly downwards. With a 1m increase in weir crest length, the water jump head position is at 0+035.56m downstream of the dam, a shift of 1m compared to the original design. With a 2m increase in weir crest length, the water jump head position is at 0+037.46m downstream of the dam, a shift of 2.9m compared to the original design. Under the weir crest lengthening scheme, the risk of water jet impacting the gate hinges is eliminated.

[0129] (2) Water level and pressure

[0130] The water level in the gate chamber and the pressure distribution on the weir surface under the original design scheme and the weir crest extension scheme (1m, 2m) are shown below (along the centerline of No. 4 spillway gate). Figure 21 , Figure 22 Corresponding to the flow diagram, under the extended weir crest scheme, the water level at the weir crest rises slightly, and the position of the hydraulic jump head shifts downward to 100m downstream of the dam. The water level lines of the original design and the extended weir crest scheme are basically consistent. The weir surface pressure is positive pressure in both cases.

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

[0132] k2 = g(position of the water jump, water level in the lock chamber, pressure on the weir surface);

[0133] In the formula, g is a function.

[0134] When calculating the second risk value k2 of the impact hinge, it is first necessary to identify the influencing factors affecting the impact hinge risk. Numerical simulation results show that the position of the hydraulic jump and the water surface line of the gate chamber have a significant impact on the impact hinge risk. Therefore, the position of the hydraulic jump and the water surface line of the gate chamber are selected as influencing factors for the second risk value k2 of the impact hinge. Weir pressure is also added as an influencing factor. This demonstrates that the selection of influencing factors can be further optimized through numerical simulation results. For example, the position of the hydraulic jump and the water surface line of the gate chamber can be selected as influencing factors for the second risk value k2 of the impact hinge, while the gate head water depth, the maximum near-bottom velocity of the gate chamber, and the discharge flow rate are no longer considered as influencing factors. This further optimizes the calculation expression for the second risk value k2, facilitating a more accurate risk assessment result.

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

[0136] k2 = m1g1 (position of the water jump head) + m2g2 (water level in the lock chamber) + m3g3 (pressure on the weir surface)

[0137] In the formula, g1, g2, and g3 are functions, and m1, m2, and m3 are coefficients, with m1 + m2 + m3 = 1. The values ​​of m1, m2, and m3 can be different, with larger values ​​indicating greater importance.

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

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

[0140] For example, in this embodiment, among the recommended schemes (schemes with a 1m and 2m increase in weir crest length) determined by numerical simulation, the scheme with a 2m increase in weir crest length is further determined to be the optimal scheme because the position of the water jump head is farther from the spur in the scheme with a 2m increase in weir crest length, and the water surface line is basically consistent with the original design scheme, and the weir surface pressure is positive pressure in both cases.

[0141] This invention provides a method for improving the flow regime of a low-head bend dam. First, by establishing a physical model of the dam and conducting hydraulic tests, problems in the preliminary design can be identified: due to the influence of the upstream bend, the water flow upstream of the dam is biased towards the right bank. Under both the verification and design conditions, a strong backflow vortex zone exists near the inlet of the right-side spillway, resulting in a poor flow regime. Downstream of the dam, the submergence is high. Under the verification condition, the hydraulic jump occurs on the steep slope of the gate chamber, with the jump head close to the gate hinge. The surface water jet poses a risk of impacting the gate hinge, potentially affecting its stability. Based on this problem, this invention optimizes the design by installing a guide wall on the first bank, close to the backflow vortex zone formed by the flow deviation, to regulate the flow and improve the flow regime. The length of the straight section of the weir crest is extended, and a wide tail pier structure is installed at the end of the gate pier to reduce the risk of surface water jet impacting the gate hinge. Furthermore, to reduce the material consumption and cost of the physical model and improve the efficiency of the physical model tests, this invention effectively combines numerical simulation and the physical model. Specifically:

[0142] First, a mathematical model of a single-hole spillway is established to study the hydraulic jump variation pattern. This allows for a rapid understanding of the improvement effects of optimization measures and a preliminary determination of the optimal solution, thereby reducing the number of modifications to the physical model. For example, in this embodiment, the physical model was only modified twice in the weir crest lengthening scheme (1m and 2m lengthening schemes), reducing the material consumption and cost of the physical model and improving the efficiency of physical model testing. Next, the optimal solution determined by the mathematical model is further confirmed through physical model testing, ultimately determining the optimal solution for the weir crest length of the spillway.

[0143] This invention, through the combined use of mathematical simulation calculations and physical model experiments, can initially determine a superior scheme based on the mathematical model, and then further confirm the superior scheme determined by the mathematical model through physical model experiments. Finally, it determines the optimal scheme for the spillway crest length / wide-tail weir structure, which can significantly reduce the number of modifications to the physical model, reduce the material consumption and cost of the physical model, and improve the efficiency of physical model experiments. Furthermore, the dual verification through mathematical simulation calculations and physical model experiments can further ensure the feasibility and accuracy of the optimized scheme. The optimized spillway can effectively reduce the risk of surface water splash impacting the gate hinges, ensuring the safe operation of the spillway, and can significantly improve the flow deviation situation above the dam, regulate the water flow, and improve the flow pattern.

[0144] Example 2

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

[0146] The floodgate described in this invention is designed using the method of Embodiment 1. By optimizing the length of the floodgate weir crest, adding a guide wall and a wide tail pier structure, the risk of surface water splash impacting the gate hinges can be effectively reduced, the flow pattern above the dam can be improved, and the safe operation of the floodgate of the dam 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 within the protection scope of the present invention.

Claims

1. A method for improving the flow regime in a low-head bend hub, characterized in that, include: S1: Establish the physical model of the hub; S2: Select typical working conditions to verify hydraulic characteristics; S3: A guide wall is set on the first bank, which is close to the backflow vortex area formed by the deflection of the water flow; the length of the straight section of the weir crest is extended and a wide tail pier structure is set at the end of the gate pier to reduce the risk of the surface water jet impacting the gate hinges. The extended length of the straight section of the weir crest and the structural form of the wide tail pier were determined through a combination of numerical and physical simulations, including: S31: Establish a mathematical model of a single outlet of the flood discharge gate, determine the boundary conditions and initial water flow of the mathematical model, and perform numerical simulation calculations; S32: Change the length of the spillway weir crest and / or the structure of the wide tail pier, and perform numerical simulation calculations respectively; S33: Based on the calculation results of S32, the first risk value of the impact hinge is... k 1. Used as a criterion to determine the optimal range of the weir crest extension length and / or the wide tail pier structure; S34: Establish a single-hole physical model of the flood discharge gate, and conduct physical model tests on schemes within the optimal range of the weir crest extension length and / or wide tail pier structure determined in S33, using the second risk value of the impact hinge. k 2. Use these as criteria to determine the optimal solution for extending the weir crest length and / or the structure of the wide tail pier; In S33, the first risk value of the impact support hinge k The expression for 1 is as follows: k 1= n 1 f 1 (Water Jump Head Position) + n 2 f 2 (leaping head water depth) + n 3 f 3 (Maximum flow velocity at the bottom of the gate chamber) + n 4 f 4 (outflow) + n 5 f 5 (Water level in the lock chamber); In the formula, f 1. f 2. f 3. f 4. f 5 are functions, n 1. n 2. n 3. n 4. n 5 represents the coefficients. n 1+ n 2+ n 3+ n 4+ n 5 = 1; In S34, the second risk value of the impact support hinge k The expression for 2 is as follows: k 2= m 1 g 1 (Water Jump Head Position) + m 2 g 2 (water level in the lock chamber) + m 3 g 3 (Weir pressure) In the formula, g 1. g 2. g 3 are functions, m 1. m 2. m 3 represents the coefficients. m 1+ m 2+ m 3 = 1.

2. The flow pattern improvement method for a low-head bend hub according to claim 1, characterized in that, In S33 n 1≥ n 2> n 3≥ n 4≥ n 5.

3. The flow pattern improvement method for a low-head bend hub according to claim 1, characterized in that, In S34 m 1≥ m 2≥ m 3.

4. The flow pattern improvement method for a low-head bend hub according to claim 1, characterized in that, The structural parameters of the wide tail pier include: tail pier type, opening width before contraction, tail pier angle, contraction ratio, outlet width, contraction section length, and pier top elevation.

5. The flow pattern improvement method for a low-head bend hub according to claim 1, characterized in that, The guide wall in S3 is a figure-eight guide wall.

6. The flow pattern improvement method for a low-head bend hub according to claim 1, characterized in that, S3 further includes extending the slope line of the first bank outward.

7. A method for improving the flow regime of a low-head bend hub according to any one of claims 1-6, characterized in that, The typical operating conditions in S1 include: verification operating conditions, design operating conditions, and energy dissipation and shock protection operating conditions.

8. A low-head bend hub, characterized in that, This method is designed using a flow regime improvement method for a low-head bend hub as described in any one of claims 1-7.

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