A method for calibrating discharge curves of cascade navigation and power hubs

Abstract

The present invention provides a method for calibrating discharge curves for cascade navigation and hydropower hubs, utilizing a combination of prototype observations, one-dimensional hydraulic formula calculations, and three-dimensional CFD numerical simulations. The method includes: prototype observations under gate-controlled discharge conditions serve to calibrate the empirical coefficients in the hydraulic formulas and verify the three-dimensional CFD numerical simulations; verified three-dimensional CFD numerical simulations under gate-open discharge conditions serve to calibrate the empirical coefficients in the one-dimensional hydraulic formulas; and a one-dimensional hydraulic formula calculation method under both controlled and open discharge conditions plays the primary computational role. Calibration considers the impact of downstream water level changes on discharge capacity, resulting in a family of curves for discharge curves under controlled discharge conditions that vary with upstream and downstream water levels and gate openings, while a family of curves for discharge curves under open discharge conditions that vary with upstream and downstream water levels. This method can address the issue of inaccurate flood discharge scheduling for existing cascade reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of hydraulic calculation for flood discharge scheduling of cascade navigation and power hubs, and in particular to a method for calibrating discharge curves of cascade navigation and power hubs. Background Art

[0002] The discharge curve is the basic characteristic curve of the water regulation system, which is directly involved in the water balance analysis and calculation of cascade hubs and the water regime forecast of the basin. Its accuracy affects the rationality and scientificity of the cascade reservoir operation plan. The Q curve is mainly obtained through hydraulic calculation and hydraulic model test in the engineering design stage. 闸 ~H0 discharge curve, but this curve is only applicable to a specific set of downstream water level-flow relationships (the current or long-term water level-flow relationship calculated based on hydrological data during the design phase). After the hub is built and operated for a period of time, the discharge capacity of the cascade hub will be significantly affected by flow changes during the joint operation of the cascade hub, the supporting effect of the downstream cascade, siltation in front of the reservoir, downcutting of the terrain behind the dam, and the time lag effect of water propagation between the cascades. Therefore, there is a deviation between the hub inflow calculated by reverse calculation of the original design discharge curve and the outflow reported by the upper-level hub. The mismatch between the flow of the upstream and downstream cascades leads to water imbalance. In addition, for cascade reservoirs, with the real-time operation and adjustment of the hubs at all levels, the inflow and outflow boundary conditions between the hubs at all levels are constantly changing, resulting in a large difference between the actual discharge capacity of the hub and the designed discharge curve, which restricts the precise operation and comprehensive benefits of the cascade hub. Therefore, carrying out the calibration of discharge curves for cascade hubs can assist in the precise joint dispatch of cascade navigation and power hubs, and provide scientific support for cascade hubs to further realize the comprehensive benefits of shipping, power generation, flood control, etc.

[0003] At present, the commonly used methods for calibrating the discharge curve include hydraulic theory formula calculation, prototype observation, hydraulic model test, etc. Theoretical calculation involves issues such as the selection of theoretical formulas and the determination of parameter values; the prototype observation method is most consistent with the actual situation and is one of the commonly used methods for calibrating the discharge curve of the sluice gate, but it has disadvantages such as uncontrollable observation conditions, limited observation data, and high observation costs, making it difficult to obtain a complete discharge curve. The hydraulic model test method has high accuracy, but it also has disadvantages such as high cost and long cycle. The specific introduction is as follows:

[0004] (1) Calculation method of hydraulic theory formula

[0005] The bottom sill of the cascade navigation and hydropower station is generally a wide-crowned weir. Based on the relationship between the gate opening e and the water head H above the weir in front of the gate, the flow pattern of the sluice gate can be divided into weir flow and gate hole outflow: when e / H ≤ 0.65, it is gate hole outflow; when e / H > 0.65, it is weir flow. The determination of free outflow and submerged outflow of the sluice gate is related to the water depth upstream and downstream of the weir crest: when When , the gate hole is free outflow; when When the gate hole is submerged outflow; where h s is the downstream water depth above the weir crest, and H0 is the total head at the weir crest.

[0006] ①Weir flow calculation formula

[0007] Under the weir flow regime, discharge calculations must consider the effects of submergence and lateral contraction:

[0008]

[0009] Where m is the discharge coefficient of the wide crest weir, ε is the side contraction coefficient, n is the number of openings, b is the net width of a single hole, σ s is the flooding coefficient of the broad crest weir, and H0 is the total water head at the weir crest.

[0010] ② Calculation formula for gate outflow

[0011] The calculation formula for the gate hole outflow flow is as follows:

[0012]

[0013] Where μ is the free outflow coefficient of the wide crest weir gate hole, σ s is the flooding coefficient of the gate hole outflow (taken as 1.0 when the gate hole is free to flow), n is the number of open holes, b is the net width of a single hole, e is the gate hole opening, and H0 is the total water head at the weir top.

[0014] The calculation of hydraulic formula depends on the empirical coefficient, the layout and size of the project and the relationship between the downstream water level and flow. At present, it is often calculated by combining the discharge flow calculation formula and the relationship between the downstream water level and flow. The specific process is as follows: Figure 1 As shown in Figure 1, the discharge curve depends on a fixed downstream water level-flow relationship. However, during the operation of the navigation and power hub, the flooding state below the gate is unstable due to the impact of the downstream reservoir's support and riverbed changes, which has a significant impact on the flooding coefficient. When the downstream water level-flow relationship changes, the discharge curve also changes.

[0015] (2) Prototype observation method

[0016] While the prototype observation method is the most intuitive and accurate way to calibrate discharge curves, it suffers from issues such as unstable inflow and uncertain observation conditions. For example, large fluctuations in upstream and downstream water levels during flow measurement, unstable discharge during open discharge, or excessive downstream discharge causing large fluctuations in river water levels can all lead to inaccurate discharge rates derived from prototype observations. Furthermore, due to the significant time and expense associated with prototype observations, calibrating all discharge curves using the prototype observation method alone is difficult.

[0017] (3) Hydraulic model test method

[0018] While hydraulic model testing offers high accuracy in calibrating discharge curves, it also has drawbacks such as high cost and a long cycle. This is particularly true for cascade navigation and hydropower hubs, where downstream hub support, sedimentation in front of the reservoir, and downstream riverbed incision can cause changes in the water level-discharge relationship downstream of the dam. Furthermore, cascade joint scheduling causes upstream and downstream boundary conditions to continuously change, and hydraulic model testing cannot address the issue of hub discharge curves changing with boundary conditions. Summary of the Invention

[0019] In order to solve the problem that the discharge curve of the existing cascade hub is inaccurate under complex and changing environment, thereby affecting the rationality and scientificity of the formulation of cascade reservoir scheduling plan, the present invention proposes a discharge curve calibration method.

[0020] A method for calibrating discharge curves of cascade navigation and power hubs is provided. The discharge curve calibration is performed under open discharge and controlled discharge conditions, respectively, and includes:

[0021] Calibration of the discharge curve under controlled discharge conditions: This method uses a combination of prototype observations, one-dimensional hydraulic formula calculations, and three-dimensional CFD numerical simulations. The prototype observations are used to calibrate the empirical coefficients in the one-dimensional hydraulic formulas, providing a basis for verification of the three-dimensional CFD numerical simulations to verify their accuracy. Specifically, the one-dimensional hydraulic formula calculations and three-dimensional CFD numerical simulation results are compared with the prototype observation data, and the deviation in discharge flow values ​​must be controlled within 5%. Based on the verification of the accuracy of the one-dimensional hydraulic formula calculations and three-dimensional CFD numerical simulations, the discharge curve is interpolated and extrapolated to provide a discharge curve under controlled discharge conditions.

[0022] Calibration of discharge curve under open discharge conditions: The discharge curve is calibrated using one-dimensional hydraulic formula calculation and three-dimensional CFD numerical simulation methods, among which one-dimensional hydraulic formula calculation is the main calculation means, and three-dimensional CFD numerical simulation provides verification for the one-dimensional hydraulic formula calculation.

[0023] Furthermore, the discharge curve calibration under the discharge control working condition specifically includes:

[0024] Step 1: Prototype Observation

[0025] Prototype observation methods are used to measure the water level and flow rate upstream and downstream of the sluice gate under controlled discharge conditions. No less than three measurement conditions are required. Flow rate measurement is performed using a traveling ADCP, and water level observation is performed using a liquid level transmitter and a paperless recorder to measure and record water level changes during the observation period.

[0026] Step 2: 3D CFD numerical simulation and 1D hydraulic formula calculation verification

[0027] Based on the prototype observation conditions, three-dimensional CFD numerical simulation and one-dimensional hydraulic formula are used to calculate the discharge flow of the sluice gate under various working conditions. At least three working conditions are selected for comparison with the prototype observation results. If the calculation deviation between the two is within 5%, it means that the three-dimensional CFD numerical simulation method and one-dimensional hydraulic calculation formula used are accurate and reliable. If the deviation is greater than 5%, it is necessary to adjust the three-dimensional numerical calculation method and the empirical coefficient in the calibrated calculation formula until the deviation is within 5%.

[0028] Step 3: Calculate the discharge flow and draw the discharge curve under controlled discharge conditions

[0029] Using calibrated hydraulic calculation formulas, the discharge flow is calculated under different combinations of upstream and downstream water levels and gate openings. For any upstream water level, the discharge flow varies with the downstream water level and gate opening. The discharge flow is represented by multiple discharge curves that vary with the downstream water level at different gate openings. Discharge curves are plotted separately for different upstream water levels. Under controlled discharge conditions, the discharge flow is represented by multiple sets of curves that vary with the upstream and downstream water levels and gate openings.

[0030] Step 4: Apply the discharge curve

[0031] Under the controlled discharge condition, the water level and gate opening upstream and downstream of the spillway are monitored in real time, and the accurate flow rate of the gate opening is obtained by interpolating in the family of discharge curves; or the required discharge flow rate is known, and the gate opening change is interpolated to formulate the dispatching rules of the spillway.

[0032] Furthermore, in step 2, the accuracy verification of the 3D CFD numerical simulation specifically includes:

[0033] A three-dimensional CFD mathematical model of the sluice gate was established. The simulation range of the mathematical model of the sluice gate can reflect the actual status of the project. The upstream boundary was selected to be the section where the water flow velocity approaches zero, and the downstream boundary was selected to be the section where the flow state is stable and the water level fluctuation is small.

[0034] The calculation model is given a total pressure boundary condition at the upstream boundary and a static pressure boundary condition at the downstream boundary. The upstream boundary is the total head including the flow velocity, and the downstream boundary is the head excluding the flow velocity.

[0035] The three-dimensional area is numerically solved to obtain the calculated flow rate of the gate hole, which is compared with the measured flow rate. The calculated deviation between the two is within 5%, indicating that the three-dimensional CFD numerical simulation is reliable. If the calculated deviation is greater than 5%, the numerical solution method is adjusted until the maximum deviation requirement is met.

[0036] Furthermore, in step 2, the verification of the one-dimensional hydraulic calculation formula specifically includes:

[0037] Under controlled discharge conditions, the gate flow rate formula is as follows:

[0038]

[0039] Where Q is the discharge flow rate of the gate hole, σ s is the flooding coefficient of the gate hole outflow, μ is the discharge coefficient of the free outflow of the wide-top weir gate hole, n is the number of open holes, b is the net width of a single hole, e is the gate hole opening, and H0 is the total water head at the weir top;

[0040] The coefficients used in the calculation are the discharge coefficient μ and the flooding coefficient σ. s ;

[0041] For the gate hole of the radial gate, the discharge coefficient μ is calculated by the following empirical formula:

[0042]

[0043] Where, is the velocity coefficient, α is the angle between the tangent line of the lower edge of the gate and the horizontal direction, and for the wide crest weir type gate hole with zero sill height, For the wide crested weir type gate hole with bottom sill,

[0044] Gate hole submerged outflow submerged coefficient σ s Ratio of undercurrent (h t -h c ”) / (Hh c ”) related, where h t is the downstream water depth, h c " is the shrinkage depth h c The conjugate water depth is H, and H is the head in front of the weir excluding the velocity head in front of the weir.

[0045] Furthermore, the discharge curve calibration under the open discharge condition specifically includes:

[0046] Step 1: Verification of hydraulic calculation results

[0047] First, the flow rate of the sluice gate is calculated using the hydraulic formula. At least three operating conditions are selected for comparison with the numerical simulation results. If the deviation between the two calculations is within 5%, the hydraulic calculation formula is reliable. Otherwise, the empirical coefficient in the hydraulic calculation formula is calibrated until the maximum deviation requirement is met.

[0048] For the wide crested weir of the navigation and power hub, the open discharge condition is mostly submerged outflow, according to the following formula:

[0049]

[0050] Where m is the discharge coefficient of the wide crest weir, ε is the side contraction coefficient, n is the number of openings, b is the net width of a single hole, σ s is the flooding coefficient of the broad crest weir, H0 is the total water head at the weir crest;

[0051] The coefficients that need to be calibrated in the formula are the discharge coefficient m of the broad crest weir, the lateral contraction coefficient ε and the submergence coefficient σ s ;

[0052] (1) Flow coefficient m

[0053] The discharge coefficient m of a broad-crowned weir depends on the inlet form of the weir crest and the relative height P / H of the weir. When the weir crest inlet is a right-angled broad-crowned weir, the discharge coefficient is:

[0054]

[0055] When the weir top inlet is rounded, the discharge coefficient is:

[0056]

[0057] The above empirical formula is applicable to 0≤P / H≤3; when P / H>3, the discharge coefficient of the wide crest weir with right-angle inlet and rounded-angle inlet is 0.32 and 0.36 respectively;

[0058] (2) Lateral contraction coefficient ε

[0059] For a multi-hole wide crest weir with side piers and gate piers, the lateral contraction coefficient ε is the weighted average of the side holes and the middle hole:

[0060]

[0061] Among them, ε' is the shrinkage coefficient of the middle hole side, and ε" is the shrinkage coefficient of the side hole side, which are calculated as follows:

[0062]

[0063] Where α0 is the coefficient considering the shape of the pier head and the weir crest entrance, d is the thickness of the gate pier, and Δ is the calculated thickness of the side pier;

[0064] (3) Submergence coefficient σ s

[0065] When the downstream water level is low, the broad crest weir is free outflow, and the flooding coefficient σ s Take 1.0; when the downstream water level is high, the broad crest weir is submerged outflow, and the specific submergence judgment condition is the downstream water depth above the weir crest h s ≥(0.75~0.85)H0:

[0066] Step 2: Calculation of discharge flow and drawing of discharge curve under open discharge conditions

[0067] Using the calibrated hydraulic calculation formula, the flow rate is calculated under different upstream and downstream water level combinations. For each upstream water level, the downstream water level can be any level between the gate bottom elevation and the upstream water level. Under each upstream water level condition, a discharge curve is obtained showing the change of discharge rate with downstream water level. Under open discharge conditions, the discharge curve can be expressed as a family of curves showing the change of discharge rate with upstream and downstream water levels.

[0068] Step 3: Apply the discharge curve

[0069] Under open discharge conditions, the water levels upstream and downstream of the sluice gate are monitored in real time, and the flow rate under open discharge conditions is obtained by interpolating in the discharge curve family.

[0070] The present invention combines prototype observation, one-dimensional hydraulic calculation formula, and three-dimensional CFD numerical simulation calculation, integrates the advantages of various means, and calibrates the discharge curve of the cascade hub in a complex and changing environment by combining the three means; the present invention takes into account the impact of downstream water level changes on the discharge flow, and the final calibrated discharge curve is a family of multiple groups of curves in which the discharge flow changes with the upstream and downstream water levels and the gate opening. Through the family of curves, the discharge flow under any combination of upstream and downstream water levels and gate openings can be checked, providing an accurate flow basis for the hub flood discharge scheduling. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 This is a commonly used flow chart for calculating discharge flow by combining hydraulic calculation formulas with the downstream water level-flow relationship.

[0072] Figure 2 This is a flow chart of a method for calibrating a discharge curve of a cascade navigation and power hub provided by an embodiment of the present invention;

[0073] Figure 3 This is a family of curves showing how the discharge rate changes with the downstream water level and gate opening under a fixed upstream water level under the controlled discharge working condition of the embodiment of the present invention (different upstream water levels correspond to different discharge rate curve families);

[0074] Figure 4 This is a family of discharge curves showing how the discharge flow changes with upstream and downstream water levels under open discharge conditions in an embodiment of the present invention. DETAILED DESCRIPTION

[0075] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0076] like Figure 2 As shown, an embodiment of the present invention proposes a method for calibrating discharge curves for cascaded navigation and hydropower hubs. This method considers the impact of downstream water level changes on discharge flow. The resulting calibrated discharge curves are represented as a family of curves that vary with upstream and downstream water levels and sluice openings. This family of curves can be used to determine the discharge flow for any combination of upstream and downstream water levels and sluice openings, providing an accurate flow basis for hub flood discharge scheduling. The discharge curve calibration method is performed separately for open discharge and controlled discharge conditions.

[0077] (1) Controlled discharge conditions

[0078] Under the controlled discharge condition, a combination of prototype observation, one-dimensional hydraulic calculation and three-dimensional CFD numerical simulation is adopted, among which one-dimensional hydraulic calculation is the main calculation method, and prototype observation serves to verify the other two methods. The empirical coefficients in the hydraulic formula are calibrated through prototype observation, and a verification basis is provided for the three-dimensional CFD numerical simulation to verify the accuracy of the three-dimensional CFD numerical simulation. The calculation results of the one-dimensional hydraulic formula calculation and the three-dimensional CFD numerical simulation are compared with the prototype observation data, and the calculated discharge flow value deviation is within 5%. On the basis of verifying the accuracy of the one-dimensional hydraulic calculation and the three-dimensional CFD numerical simulation, the discharge curve is interpolated and extended to give the calibrated discharge curve under the controlled discharge condition. The specific implementation process of the controlled discharge condition is as follows:

[0079] Step 1: Prototype Observation

[0080] First, a prototype observation method was used to measure upstream and downstream water levels and flow rates under controlled release conditions, with at least three measurement conditions. Flow rates were measured using a traveling ADCP, while water levels were observed using a level transmitter and paperless recorder to measure and record water level changes during the observation period.

[0081] ADCP flow measurement sections must account for uncertainties such as large water level fluctuations near the dam and significant intermediate water losses in areas far from the dam. Optimally, the flow measurement section should be located within 1.5 km of the dam, with minimal water level fluctuations and no tributaries or water intakes.

[0082] Preferably, the ADCP instrument is equipped with a 9-beam system, including 2 groups of 4 beams each for measuring velocity profiles (each group has a different operating frequency) and 1 vertical beam for measuring water depth.

[0083] Upstream and downstream water level monitoring points must be arranged at locations where water level fluctuations are small and the water flow velocity is basically zero, such as within the hub navigation channel.

[0084] Step 2: 3D CFD numerical simulation and 1D hydraulic formula calculation and parameter calibration

[0085] Based on the prototype's observed operating conditions, calculate the discharge flow rate of the sluice gate under various operating conditions using three-dimensional CFD numerical simulation and one-dimensional hydraulic calculation formulas. Compare at least three operating conditions with the prototype's observed results. If the calculated deviation between the two is within 5%, the three-dimensional CFD numerical simulation method and one-dimensional hydraulic calculation formula used are accurate and reliable. If the deviation is greater than 5%, adjust the three-dimensional numerical calculation method and the empirical coefficients in the calibrated one-dimensional calculation formula until the deviation is within 5%.

[0086] (1) Verification of the accuracy of three-dimensional CFD numerical simulation

[0087] A three-dimensional CFD mathematical model of the spillway is established. The scope of the mathematical model of the spillway should be able to reflect the actual status of the project. The upstream boundary should be the section where the water flow velocity approaches zero, and the downstream boundary position should be selected from the section with stable flow and small water level fluctuation.

[0088] The total pressure boundary condition is given at the upstream calculation boundary of the calculation model, and the static pressure boundary condition is given at the downstream. The upstream boundary is the total head including the traveling flow velocity, and the downstream boundary is the head excluding the traveling flow velocity.

[0089] The three-dimensional area is numerically solved to obtain the calculated flow rate of the gate hole, which is compared with the measured flow rate. The calculated deviation between the two is within 5%, indicating that the three-dimensional numerical calculation method is reliable. If the calculated deviation is greater than 5%, the numerical solution method is adjusted until the maximum deviation requirement is met.

[0090] The calibrated three-dimensional CFD numerical simulation method provides a calculation basis for subsequent open-discharge conditions.

[0091] (2) One-dimensional hydraulic formula calculation and parameter calibration

[0092] Under the controlled discharge condition, the gate flow rate formula is shown in formula (2). The coefficients that need to be calculated in the formula are the flow coefficient μ and the flooding coefficient σ s .

[0093] According to research by Wuhan University, for the gate opening of a radial gate, the flow coefficient μ can be calculated using the following empirical formula:

[0094]

[0095] Where α is the angle between the tangent line of the lower edge of the gate and the horizontal direction. In actual use, for the wide crested weir gate hole with zero sill height, For wide crested weir gate holes with bottom sill,

[0096] Gate hole submerged outflow submerged coefficient σ s Ratio of undercurrent (h t -h c ”) / (Hh c”) related (H is the head before the weir excluding the head of the flow velocity before the weir, h t is the downstream water depth, h c " is the shrinkage depth h c The conjugate water depth of ) can be selected according to Table 1.

[0097] Table 1 Submergence coefficients corresponding to different underflow ratios of submerged outflow from the gate hole of the wide crest weir

[0098] 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.92 0.94 0.96 0.98 0.99 0.995 1.0 0.86 0.78 0.71 0.66 0.59 0.52 0.45 0.36 0.23 0.19 0.16 0.12 0.07 0.04 0.02

[0099] Select several working conditions and compare the gate discharge calculated by formula (2) with the three-dimensional numerical calculation results. According to the discharge of three-dimensional numerical simulation, the flow coefficient μ in formula (2) is calibrated. Under the submerged outflow condition, the submergence coefficient σ is also required to be calibrated. s , and obtain the empirical coefficient in formula (2). The calibrated formula provides a basis for calculating the excess flow rate under controlled discharge conditions under other working conditions.

[0100] Step 3: Calculate the discharge flow and draw the discharge curve under controlled discharge conditions

[0101] On the basis of verifying the accuracy of the hydraulic calculation formula, the sluice discharge under different upstream and downstream water levels and gate opening combinations is calculated according to the calibrated hydraulic calculation formula (2). For any upstream water level condition, the discharge flow varies with the downstream water level and sluice opening. The discharge flow is a number of discharge curves that vary with the downstream water level under different gate openings, and are drawn separately according to different upstream water levels, such as Figure 3 Therefore, under the controlled discharge condition, the discharge flow can be expressed as a family of multiple curves that vary with the upstream and downstream water levels and the gate opening.

[0102] Step 4: Apply the discharge curve

[0103] Under the controlled discharge condition, the water level and gate opening upstream and downstream of the sluice gate are monitored in real time, and the accurate flow rate of the gate opening is obtained by interpolating in the discharge curve family; or the change in gate opening is interpolated based on the known discharge flow rate to formulate the scheduling rules of the sluice gate.

[0104] (2) Open discharge condition

[0105] Under open discharge conditions, due to the difficulty of prototype observation, the discharge curve is calibrated using one-dimensional hydraulic formula calculation and three-dimensional CFD numerical simulation method. The one-dimensional hydraulic calculation is the main calculation method, and the three-dimensional CFD numerical simulation provides verification for the one-dimensional calculation. The specific implementation process of the open discharge condition is as follows:

[0106] Step 1: Calculation and verification of hydraulic formulas and parameter calibration

[0107] First, the hydraulic calculation formula is used to calculate the discharge flow of the sluice gate under various working conditions. At least three working conditions are selected for comparison with the results of the three-dimensional numerical simulation method. If the calculation deviation between the two is within 5%, it means that the hydraulic calculation formula is reliable. Based on the numerical calculation of the discharge flow, the flow coefficient m and the flooding coefficient σ in formula (1) are calibrated. s The calibration method is the same as that of the controlled leakage condition.

[0108] (1) Flow coefficient m

[0109] The discharge coefficient m of a broad-crowned weir depends on the inlet form of the weir crest and the relative height P / H of the weir. When the weir crest inlet is a right-angled broad-crowned weir, the discharge coefficient is:

[0110]

[0111] When the weir top inlet is rounded, the discharge coefficient is:

[0112]

[0113] The above empirical formula applies when 0 ≤ P / H ≤ 3. When P / H > 3, the discharge coefficients for the wide-crested weir are 0.32 and 0.36 for the right-angle and rounded-angle inlets, respectively. As can be seen from the formula, the maximum discharge coefficient for the wide-crested weir is 0.385.

[0114] (2) Lateral contraction coefficient ε

[0115] For a multi-hole wide crest weir with side piers and gate piers, the lateral contraction coefficient ε is the weighted average of the side holes and the middle hole:

[0116]

[0117] Among them, ε' is the shrinkage coefficient of the middle hole side, and ε" is the shrinkage coefficient of the side hole side, which are calculated as follows:

[0118]

[0119] Where α0 is the coefficient considering the shape of the pier head and the weir crest entrance (α0 = 0.1 when the pier head is arc-shaped), d is the pier thickness, and Δ is the calculated thickness of the side pier.

[0120] (3) Submergence coefficient σ s

[0121] When the downstream water level is low, the broad crest weir is free outflow, and the flooding coefficient σ s Take 1.0; when the downstream water level is high, the broad crest weir is submerged outflow, and the specific submergence judgment condition is the downstream water depth above the weir crest h s ≥(0.75~0.85)H0, flooding coefficient σ s Decreases with increasing relative submergence:

[0122] The calculation formula of the flooding coefficient in the Sluice Design Code is:

[0123]

[0124] Yuan Xinming et al. pointed out that the above formula is not accurate when the flooding degree is greater than 0.9, and put forward a formula that is applicable to 0.9≤h s The calculation formula for the flooding coefficient of a high flooding flat-bottomed wide-crowned weir with H0 < 1.0 is:

[0125]

[0126] Step 2: Calculation of discharge flow and drawing of discharge curve under open discharge conditions

[0127] According to the calibrated flow calculation formula, the flow is calculated under different upstream and downstream water level combinations. For each upstream water level, the downstream can take any water level between the gate bottom elevation and the upstream water level elevation. Therefore, for each upstream water level, a discharge curve showing the change of discharge flow with downstream water level can be obtained. Finally, under the open discharge condition, the discharge curve is a family of curves showing the change of discharge flow with downstream water level under different upstream water levels, such as Figure 4 shown.

[0128] Step 3: Apply the discharge curve

[0129] Under open discharge conditions, the water levels upstream and downstream of the spillway are monitored in real time, and the accurate flow rate of the sluice hole can be finally obtained by interpolating in the family of discharge curves.

[0130] Verification was carried out in a certain project and found that the discharge flow obtained by the discharge curve provided by the present invention deviated from the on-site measured flow within 5%. This shows that the discharge curve calibration method provided by the present invention is accurate and reliable, and can provide an accurate flow basis for flood discharge scheduling of cascade navigation and power hubs.

[0131] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for calibrating discharge curves of cascade navigation and power hubs, characterized in that: The discharge curve calibration is divided into open discharge and controlled discharge conditions and is carried out separately, including: discharge curve calibration under controlled discharge conditions: using a combination of prototype observation, one-dimensional hydraulic formula calculation and three-dimensional CFD numerical simulation methods, wherein the empirical coefficients in the one-dimensional hydraulic calculation formula are calibrated through prototype observation, and a verification basis is provided for the three-dimensional CFD numerical simulation to verify the accuracy of the three-dimensional CFD numerical simulation. Specifically, the one-dimensional hydraulic formula calculation and three-dimensional CFD numerical simulation results are compared with the prototype observation data, and the deviation of the discharge flow value must be controlled within 5%; on the basis of verifying the accuracy of the one-dimensional hydraulic formula calculation and three-dimensional CFD numerical simulation, the discharge curve is interpolated and extended to give the discharge curve under controlled discharge conditions; Calibration of discharge curve under open discharge conditions: The discharge curve is calibrated using one-dimensional hydraulic formula calculation and three-dimensional CFD numerical simulation methods, with one-dimensional hydraulic formula calculation as the main calculation method and three-dimensional CFD numerical simulation providing verification for the one-dimensional hydraulic formula calculation; The discharge curve calibration under the controlled discharge condition specifically includes: Step 1: Prototype Observation Prototype observation methods are used to measure the water level and flow rate upstream and downstream of the sluice gate under controlled discharge conditions. No less than three measurement conditions are required. Flow rate measurement is performed using a traveling ADCP, and water level observation is performed using a liquid level transmitter and a paperless recorder to measure and record water level changes during the observation period. Step 2: 3D CFD numerical simulation and 1D hydraulic formula calculation verification Based on the prototype observation conditions, three-dimensional CFD numerical simulation and one-dimensional hydraulic formula are used to calculate the discharge flow of the sluice gate under various working conditions. At least three working conditions are selected for comparison with the prototype observation results. If the calculation deviation between the two is within 5%, it means that the three-dimensional CFD numerical simulation method and one-dimensional hydraulic calculation formula used are accurate and reliable. If the deviation is greater than 5%, it is necessary to adjust the empirical coefficients in the three-dimensional numerical calculation method and the calibrated hydraulic calculation formula until the deviation is within 5%. Step 3: Calculate the discharge flow and draw the discharge curve under controlled discharge conditions The calibrated hydraulic calculation formula is used to calculate the discharge flow under different combinations of upstream and downstream water levels and gate openings. For any upstream water level condition, the discharge flow varies with the downstream water level and gate opening. The discharge flow is represented by multiple discharge flow curves that vary with the downstream water level under different gate openings. The discharge flow curves are drawn separately for different upstream water levels. Under the controlled discharge condition, it can be expressed as a family of curves showing the discharge flow varying with the upstream and downstream water levels and gate opening. Step 4: Apply the discharge curve Under controlled discharge conditions, the upstream and downstream water levels and gate opening of the sluice gate are monitored in real time, and the accurate flow rate of the gate opening is obtained by interpolating in the discharge curve family; or the required downstream flow rate is known, and the gate opening change is interpolated to formulate the scheduling rules of the sluice gate.

2. The method for calibrating the discharge curve of a cascade navigation and power hub according to claim 1, wherein: In step 2, the accuracy verification of the 3D CFD numerical simulation specifically includes: A three-dimensional CFD mathematical model of the sluice gate was established. The simulation range of the mathematical model of the sluice gate can reflect the actual status of the project. The upstream boundary was selected to be the section where the water flow velocity approaches zero, and the downstream boundary was selected to be the section where the flow state is stable and the water level fluctuation is small. The calculation model is given a total pressure boundary condition at the upstream boundary and a static pressure boundary condition at the downstream boundary. The upstream boundary is the total head including the flow velocity, and the downstream boundary is the head excluding the flow velocity. The three-dimensional area is numerically solved to obtain the calculated flow rate of the gate hole, which is compared with the measured flow rate. The calculated deviation between the two is within 5%, indicating that the three-dimensional numerical calculation method is reliable. If the calculated deviation is greater than 5%, the numerical solution method is adjusted until the maximum deviation requirement is met.

3. The method for calibrating the discharge curve of a cascade navigation and power hub according to claim 1, wherein: In step 2, the verification of the one-dimensional hydraulic calculation formula specifically includes: Under controlled discharge conditions, the gate flow rate formula is as follows: ； Where Q is the discharge flow rate of the gate hole, σ s is the flooding coefficient of the gate hole outflow, μ is the discharge coefficient of the free outflow of the wide-top weir gate hole, n is the number of open holes, b is the net width of a single hole, e is the gate hole opening, and H0 is the total water head at the weir top; The coefficients used in the calculation are the discharge coefficient μ and the flooding coefficient σ. s ; For the gate hole of the radial gate, the discharge coefficient μ is calculated by the following empirical formula: ； Where φ is the velocity coefficient, α is the angle between the tangent line of the lower edge of the gate and the horizontal direction. For a wide-crowned weir gate with zero sill height, φ=0.95~1.0 is used; for a wide-crowned weir gate with a bottom sill, φ=0.85~0.95 is used. Gate hole outflow submergence coefficient σ s Ratio of undercurrent (h t -h c ”) / (Hh c ”) related, where h t is the downstream water depth, h c " is the shrinkage depth h c The conjugate water depth is H, and H is the head in front of the weir excluding the velocity head in front of the weir.

4. The method for calibrating the discharge curve of a cascade navigation and power hub according to claim 1, wherein: The discharge curve calibration under the open discharge condition specifically includes: Step 1: Verification of hydraulic formula calculation results First, the flow rate of the sluice gate is calculated using hydraulic formulas. At least three operating conditions are selected and compared with the results calculated by the three-dimensional numerical simulation method. If the deviation between the two calculations is within 5%, it means that the hydraulic calculation formula is reliable. Otherwise, the empirical coefficient in the hydraulic calculation formula is calibrated until the maximum deviation requirement is met. For the crest weir, the open discharge condition is mostly submerged outflow, according to the following formula: ； Where m is the discharge coefficient of the wide crest weir, ε is the side contraction coefficient, n is the number of openings, b is the net width of a single hole, σ s is the flooding coefficient of the broad crest weir, H0 is the total water head at the weir crest; The coefficients that need to be calibrated in the formula are the discharge coefficient m of the broad crest weir, the lateral contraction coefficient ε and the submergence coefficient σ s ; (1) Flow coefficient m The discharge coefficient m of a broad-crowned weir depends on the inlet form of the weir crest and the relative height P / H of the weir. When the weir crest inlet is a right-angled broad-crowned weir, the discharge coefficient is: ； When the weir top inlet is rounded, the discharge coefficient is: ； The above empirical formula is applicable to 0≤P / H≤3; when P / H>3, the discharge coefficient of the wide crest weir with right-angle inlet and rounded-angle inlet is 0.32 and 0.36 respectively; (2) Lateral contraction coefficient ε For a multi-hole wide crested weir with side piers and gate piers, the lateral contraction coefficient ε is the weighted average of the contraction coefficients of the side holes and the middle hole: ； Among them, ε' is the shrinkage coefficient of the middle hole side, and ε" is the shrinkage coefficient of the side hole side, which are calculated as follows: ； ； Where α0 is the coefficient considering the shape of the pier head and the weir crest entrance, d is the thickness of the gate pier, and Δ is the calculated thickness of the side pier; (3) Submergence coefficient σ s When the downstream water level is low, the broad crest weir is free outflow, and the flooding coefficient σ s Take 1.0; when the downstream water level is high, the broad crest weir is submerged outflow, and the specific submergence judgment condition is the downstream water depth above the weir crest h s ≥(0.75~0.85)H0; Step 2: Calculation of discharge flow and drawing of discharge curve under open discharge conditions Using the calibrated hydraulic calculation formula, the flow rate is calculated under different upstream and downstream water level combinations. For each upstream water level, the downstream water level can be any level between the gate bottom elevation and the upstream water level. Under each upstream water level condition, a discharge curve is obtained showing the change of discharge rate with downstream water level. Therefore, under open discharge conditions, the discharge curve can be expressed as a family of curves showing the change of discharge rate with upstream and downstream water levels. Step 3: Apply the discharge curve Under open discharge conditions, the water levels upstream and downstream of the sluice gate are monitored in real time, and the flow rate under open discharge conditions is obtained by interpolating in the discharge curve family.

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