Characteristic curve simulation method based on S-region unsteady CFD correction

Abstract

The invention relates to the technical field of flow simulation of pump turbines, and discloses a characteristic curve simulation method based on S-zone unsteady CFD (computational fluid dynamics) correction, which comprises the following steps of: performing CFD steady calculation on different guide vane openings to obtain a characteristic curve of a pump turbine set; unsteady calculation is introduced into the S region, and data points of partial steady calculation are corrected; according to the method, the full characteristic curve of the pump turbine is obtained by completely adopting a numerical simulation mode, unsteady calculation is introduced into the S region, part of the data points are corrected, the difference between the characteristic curve obtained through numerical simulation and the characteristic curve measured through a test in the S region is reduced, and the characteristic curve is redrawn. And the guidance value of numerical simulation on the design of the pumped storage unit in the S area is improved.

Description

Technical Field

[0001] This invention relates to the field of pump-turbine flow simulation technology, specifically to a characteristic curve simulation method based on S-region unsteady CFD correction. Background Technology

[0002] As the core equipment for peak shaving and valley filling in the power system, pumped storage units exhibit S-zone characteristics when operating at low flow rates and low opening degrees. In the rightmost part of the four-quadrant characteristic curve, one head corresponds to 2-3 flow rates, resulting in strong flow instability. This has a significant impact on the low-load operation and transition process of pumped storage units.

[0003] Due to the large number of operating points, traditional numerical simulation methods mostly employ steady-state CFD calculations to calculate the head-flow rate relationship at a specified guide vane angle and plot the unit flow rate-unit speed curve. However, near the S-region, the strong unsteady characteristics of the flow field make the calculation difficult to converge, and the unit speed obtained by forcibly averaging along the iteration steps is generally and significantly lower than the experimental value, leading to an overestimation of the S-characteristic risk of the unit. Summary of the Invention

[0004] In view of this, the present invention provides a characteristic curve simulation method based on S-region unsteady CFD correction to solve the problem of how to correct simulation deviations in the S-region.

[0005] In a first aspect, the present invention provides a characteristic curve simulation method based on S-region unsteady CFD correction, the method comprising:

[0006] CFD steady-state calculations were performed for different guide vane openings to obtain the characteristic curves of the pump-turbine unit;

[0007] Unsteady calculations are introduced into region S, and some steady calculation data points are corrected.

[0008] The characteristic curve is redrawn using the corrected data points.

[0009] This invention uses numerical simulation to obtain the full characteristic curves of the pump-turbine, and introduces unsteady calculations in the S region to correct some data points, thereby reducing the difference between the characteristic curves obtained by numerical simulation and those obtained by experiments in the S region, and improving the guiding value of numerical simulation for the design of pumped storage units in the S region.

[0010] In one optional implementation, CFD steady-state calculations are performed on different guide vane openings to obtain the characteristic curves of the pump-turbine unit, including:

[0011] For each guide vane opening, set inlet flow boundary conditions and set uniform pressure outlet boundary conditions;

[0012] CFD steady flow calculations were performed for all boundary condition combinations for all guide vane angles to obtain head data for each working condition.

[0013] Based on the head and flow data, calculate the unit parameters for each operating condition and plot the characteristic curves for each guide vane opening.

[0014] This invention obtains head data for each operating condition by setting inlet flow boundary conditions for each guide vane opening and combining them with the guide vane angle boundary conditions, thereby covering the full operating conditions of the pump turbine and plotting characteristic curves to provide a data basis for S-region correction.

[0015] In one alternative implementation, inlet flow boundary conditions are set, including:

[0016] To obtain the approximate flow distribution range at different water heads with different guide vane openings;

[0017] Lower limit of flow rate for all openings;

[0018] Expand the flow limit for all openings;

[0019] Determine the inlet flow rate of the water pump.

[0020] This invention calculates the updated flow range for different guide vane openings to obtain the main distribution range of head and flow, limits the lower limit of flow for all openings to eliminate data that is not realistic, expands the upper limit of flow for all openings to improve the integrity of the four-quadrant characteristic curve, and determines the inlet flow of the pump direction to take into account the simulation needs of various working conditions.

[0021] In one optional implementation, CFD steady flow calculations are performed for all boundary condition combinations at all guide vane angles to obtain head data for each operating condition, including:

[0022] Based on the residual convergence criterion of head, determine whether the steady-state calculation has converged;

[0023] If the steady-state calculation converges, then the head in the calculation result of the last iteration step is determined as the final head.

[0024] If the steady-state calculation does not converge, then determine whether the head exhibits periodic changes.

[0025] If the water head changes periodically, the average water head during a specific fluctuation period is taken as the final water head.

[0026] If the water head changes monotonically, increase the upper limit of the iteration step and continue the calculation until the preset conditions are met.

[0027] This invention combines accurate convergence of head residuals with different methods to calculate head data under different conditions, making the determined head data more consistent with actual working conditions.

[0028] In one optional implementation, unsteady calculations are introduced into region S, and some steady-calculation data points are corrected, including:

[0029] Specify the non-steadyness determination value;

[0030] If the steady flow cannot meet the unsteady condition criteria, then continue the unsteady calculation for a certain physical time.

[0031] The S-characteristics are corrected by utilizing the fluctuation characteristics of the water head.

[0032] This invention specifies an unsteady criterion value and calculates a certain physical time when the steady flow does not meet the criterion value, in order to ensure that the complete S-characteristic fluctuation cycle is obtained.

[0033] In one alternative implementation, the correction method includes zero-order correction, first-order correction, and second-order correction.

[0034] This invention uses zero-order correction, first-order correction and second-order correction to correct the S-region, so as to process the simulation deviation in the S-region.

[0035] In one alternative implementation, the S-characteristic is modified, including:

[0036] To address the unsteady flow characteristics when the unit operates in the S region, a zero-order correction is employed.

[0037] To address the interference of head fluctuations on the calculation conditions, a first-order correction is adopted;

[0038] A second-order correction is adopted to address the coupled fluctuations in head and flow rate.

[0039] This invention compensates for the influence of flow fluctuations by considering the unsteady flow when the unit operates in the S region, using a zero-order correction method, considering the interference of head fluctuations on the calculation conditions, using a first-order correction to reduce the interference of head fluctuations, and considering the coupled fluctuations of head and flow rate, using a second-order correction to provide a more reliable simulation basis.

[0040] Secondly, the present invention provides a characteristic curve simulation device based on S-region unsteady CFD correction, the device comprising:

[0041] The unsteady calculation module is used to perform CFD steady-state calculations on different guide vane openings to obtain the characteristic curves of the pump-turbine unit.

[0042] The correction module is used to introduce unsteady calculations into the S region and correct some steady calculation data points.

[0043] The redraw module is used to redraw the characteristic curve using the corrected data points.

[0044] Thirdly, the present invention provides a computer device, comprising: a memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the computer instructions to perform the characteristic curve simulation method based on S-region unsteady CFD correction described in the first aspect or any corresponding embodiment.

[0045] Fourthly, the present invention provides a computer-readable storage medium storing computer instructions for causing a computer to execute the characteristic curve simulation method based on S-region unsteady CFD correction described in the first aspect or any corresponding embodiment. Attached Figure Description

[0046] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0047] Figure 1 This is a flowchart illustrating the characteristic curve simulation method based on S-region unsteady CFD correction according to an embodiment of the present invention.

[0048] Figure 2 These are schematic diagrams illustrating three correction methods according to embodiments of the present invention;

[0049] Figure 3 The deviation between the second method and the first method in the zero-order correction method according to the embodiments of the present invention;

[0050] Figure 4 This is a schematic diagram of the second-order correction according to an embodiment of the present invention;

[0051] Figure 5 This is a schematic diagram of the modified characteristic curve according to an embodiment of the present invention;

[0052] Figure 6 This is a structural block diagram of a characteristic curve simulation device based on S-region unsteady CFD correction according to an embodiment of the present invention.

[0053] Figure 7 This is a schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] The existing technology has the following problems:

[0056] (1) The existing S-characteristics of water pump turbines rely heavily on experimental measurements, and the accuracy of steady-state calculations in numerical simulations is poor. Especially in the S-region, the characteristic curves obtained from steady-state numerical simulations and experimental measurements differ significantly, particularly the calculated values ​​per unit speed, which are generally and significantly lower.

[0057] (2) Three-dimensional CFD unsteady calculation can effectively improve the calculation accuracy of S region, but it takes a long time and is not suitable for scanning calculation with different guide vane openings and different loads. There is a lack of industry standards for defining the application scenarios of unsteady calculation.

[0058] (3) There is a lack of rigorous methods for comparing simulation results and test values, as well as methods for controlling the error of simulation results. It is impossible to provide a reasonable numerical simulation correction scheme based on the difference between the calculation results and the experimental results.

[0059] According to an embodiment of the present invention, a characteristic curve simulation method based on S-region unsteady CFD correction is provided. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although the logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0060] This embodiment provides a characteristic curve simulation method based on S-region unsteady CFD correction. Figure 1 This is a flowchart of a characteristic curve simulation method based on S-region unsteady CFD correction according to an embodiment of the present invention, as shown below. Figure 1 As shown, the process includes the following steps:

[0061] Step S101: Perform CFD steady-state calculations on different guide vane openings to obtain the characteristic curves of the pump-turbine unit.

[0062] In this embodiment of the invention, scanning calculations are performed for all guide vane openings and boundary condition combinations, and the Q of the pump-turbine unit is obtained entirely through steady flow numerical simulation. 11 -n 11The curve serves as the data basis for subsequent steps.

[0063] Step S102: Introduce unsteady calculations in region S and correct some steady calculation data points.

[0064] In this embodiment of the invention, the characteristic curve of the pump-turbine exists in a special range, located at a low head and low flow rate in the turbine direction; this region is called the S-region. When the unit's operating point is in this region, the flow is highly unstable. Therefore, to overcome the problem of a large discrepancy between the characteristic curves obtained from steady-state numerical simulation and experimental measurement in the S-region, unsteady calculations are introduced to correct some data points from the steady-state calculations.

[0065] Step S103: Redraw the characteristic curve using the corrected data points.

[0066] In this embodiment of the invention, the characteristic curve is redrawn using the corrected data points to obtain a characteristic curve that is closer to the experimental method.

[0067] The characteristic curve simulation method based on S-region unsteady CFD correction provided in this embodiment obtains the full characteristic curve of the pump turbine entirely through numerical simulation, and introduces unsteady calculations in the S-region to correct some data points, thereby reducing the difference between the characteristic curve obtained by numerical simulation and the characteristic curve measured by experiment in the S-region, and improving the guiding value of numerical simulation for the design of pumped storage units in the S-region.

[0068] This embodiment provides a characteristic curve simulation method based on S-region unsteady CFD correction, the process of which includes the following steps:

[0069] Step S201: Perform CFD steady-state calculations on different guide vane openings to obtain the characteristic curves of the pump-turbine unit.

[0070] Specifically, step S201 includes:

[0071] Step S2011: Set inlet flow boundary conditions and set uniform pressure outlet boundary conditions for each guide vane opening.

[0072] Step S2012: Perform CFD steady flow calculations for all boundary condition combinations for all guide vane angles to obtain head data for each working condition.

[0073] Step S2013: Calculate the unit parameters for each operating condition based on the head data and flow rate data, and plot the characteristic curves of each guide vane opening.

[0074] In this embodiment of the invention, a series of inlet flow boundary conditions and a uniform pressure outlet boundary condition are set for each guide vane angle. CFD steady flow calculations are performed on all boundary condition combinations for all guide vane angles to obtain the convergent or average head H for each operating condition. Using the head H and flow rate Q, unit parameters for each operating condition are calculated, and characteristic curves for each guide vane opening are plotted. This embodiment of the invention primarily focuses on Q. 11 -n 11 curve.

[0075] By setting inlet flow boundary conditions for each guide vane opening and combining them with the guide vane angle boundary conditions, head data for each operating condition is obtained to cover the full operating conditions of the pump turbine. Characteristic curves are then plotted to provide a data basis for correction in the S region.

[0076] Specifically, setting the inlet flow boundary conditions in step S2011 above includes:

[0077] Step S2011a: Obtain the approximate flow distribution range at different head for different guide vane openings.

[0078] Step S2011b: Limit the lower limit of flow for all openings.

[0079] Step S2011c: Expand the flow limit for all openings.

[0080] Step S2011d: Determine the inlet flow rate of the water pump in the direction of travel.

[0081] In this embodiment of the invention, the specific curve is first calculated twice to obtain the main distribution range of head and flow rate, which serves as a reference benchmark for subsequent work.

[0082] The specific implementation process is as follows:

[0083] At 100% guide vane opening (rated operating opening), the inlet flow rate is -30% Q. r ~110% Q r The distribution is internal, with increased density near the flow rate of 0, meaning the operating points in that area are more densely distributed. If the calculation results contain operating points with negative head or very small positive head, these points should be removed, and the updated flow range λ should be provided. 100％，min Q r ~λ 35％，min Q r .

[0084] Repeat the above steps at a guide vane opening of 35% to obtain the updated flow range λ. 35％，min Q r ~λ 35％，max Q r .

[0085] Lower limit of flow rate for all openings: When the unit is running stably, there is no situation where the head is close to zero or negative. In the simulation, points where the head is close to zero or negative are represented as infinite or complex numbers on the four-quadrant characteristic curve, which is not realistic. Therefore, they need to be removed to reduce the total calculation time.

[0086] The specific implementation process is as follows:

[0087] Interpolation is performed for the applicable lower limit of flow rate for different guide vane openings, such as linear interpolation: flow rate at k% guide vane opening and Q r The lower limit of the ratio should be:

[0088]

[0089] Linear interpolation is sufficient for controlling the lower limit of flow rate. If nonlinear interpolation is required, multiple guide vane openings should be obtained repeatedly according to the above steps S2011a, an interpolation function should be selected, and then interpolation should be performed.

[0090] Maximum flow rate at full opening: Ingress flow rate is 110% of Q r At that time, the unit speed is still relatively high, especially under the condition of large opening. This causes the turbine part of the four-quadrant characteristic curve to extend insufficiently to the left, resulting in incomplete curves and insufficient information.

[0091] The specific implementation process is as follows:

[0092] First, define the minimum unit rotational speed n required for calculation. 11，min This value should be as close to 0 as possible; it is recommended that n be [value]. 11，min ≤0.1n r For example, for units with a rated operating speed of around 50 rpm, it is recommended to specify n. 11，min =5. Then, based on the data not in zone S from the two trial calculations in steps S2011a and S2011b (it is recommended to use a flow rate greater than 50% of the rated flow rate as the criterion), perform an exponential function fitting of head-flow rate to obtain the fitting relationship of H-λ:

[0093]

[0094] Where α and Q0 are the fitting coefficients.

[0095] According to the definition of unit speed, the minimum unit speed n is satisfied. 11，min The water head is:

[0096]

[0097] Where D is the characteristic diameter of the unit.

[0098] Therefore, for the opening degree calculated in the two trials, the upper limit of flow rate should be extended to:

[0099]

[0100] Finally, interpolation is performed to determine the applicable flow rate upper limit for different guide vane openings, such as linear interpolation: flow rate at k% guide vane opening and Q. r The upper limit of the ratio should be:

[0101]

[0102] The determination of the inlet flow rate in the direction of the water pump is primarily specific to the S-region of the turbine direction in this embodiment of the invention. However, if calculations are required for the water pump direction, steps S2011a and S2011b are used for both the water pump and turbine directions. For step S2011c, the degree to which the characteristic curves of different pump openings extend to the right is essentially the same; therefore, interpolation between different openings is unnecessary. Only a given n is required. 11，min The maximum flow rate can be any value λ. max or the average of the two:

[0103] λ k％，max =(λ 35％，max +λ 100％，max ) / 2

[0104] In some alternative implementations, the pressure outlet boundary conditions are set according to the following procedure:

[0105] For unidirectional flow calculations, the outlet pressure value for each operating condition has no impact on the calculation results, so it is uniformly set to atmospheric pressure (gauge pressure = 0 Pa). For multiphase flow calculations, the outlet pressure is specified according to the actual excavation depth of the power plant and the elevation of the lower reservoir water surface to ensure that the simulation and the actual machine have the same cavitation margin.

[0106] By calculating the updated flow range for different guide vane openings, the main distribution range of head and flow rate is obtained, the lower limit of flow rate for all openings is limited to eliminate data that is not realistic, the upper limit of flow rate for all openings is expanded to improve the integrity of the four-quadrant characteristic curve, and the inlet flow rate of the pump direction is determined to take into account the simulation needs of various working conditions.

[0107] Specifically, step S2012 includes:

[0108] Step S2012a: Determine whether the steady-state calculation has converged based on the residual convergence criterion of the head.

[0109] In step S2012b, if the steady-state calculation converges, the head in the calculation result of the last iteration step is determined as the final head.

[0110] In step S2012c, if the steady-state calculation does not converge, determine whether the head exhibits periodic changes.

[0111] In step S2012d, if the water head changes periodically, the average water head of a specific fluctuation period is taken as the final water head.

[0112] In step S2012e, if the water head changes monotonically, the upper limit of the iteration step is increased and the calculation continues until the preset condition is met.

[0113] In this embodiment of the invention, when determining the steady-state head, the residual convergence criterion for the head should first be specified. In this embodiment, the residual head is set to ≤10. -6 At that time, it is assumed that the steady-state calculation is convergent.

[0114] Within a given upper limit for the number of iteration steps, for any operating condition, if the steady-state calculation converges, the head from the last iteration step is used as the final head. If the steady-state calculation does not converge, the head-iteration step curve should be checked to determine if the head exhibits periodic variation. If the head exhibits periodic variation, the average of the head results from at least the last five fluctuation periods should be used as the final head. If the head exhibits monotonic variation, the upper limit for the number of iteration steps should be increased, and the calculation should continue until convergence or the head curve exhibits periodic fluctuations.

[0115] By combining accurate convergence of head residuals and using different methods to calculate head data under different conditions, the determined head data is made to better reflect the actual working conditions.

[0116] In some alternative implementations, the unit parameter is calculated as follows:

[0117]

[0118] Step S202: Introduce unsteady calculations into region S and correct some of the steady-calculation data points.

[0119] Specifically, step S202 includes:

[0120] Step S2021: Specify the non-steadyness determination value.

[0121] Step S2022: If the steady flow cannot meet the unsteady condition judgment value, then continue the unsteady calculation for a certain physical time.

[0122] Step S2023: Correct the S-characteristics by utilizing the fluctuation characteristics of the water head.

[0123] In this embodiment of the invention, an unsteady criterion value is first established. For steady flow conditions that cannot meet the unsteady criterion value, unsteady calculations are performed for a certain physical time to obtain the peak-to-peak value and spectral characteristics of the head H in its stable fluctuation range. The fluctuation characteristics of the head H are then used to perform a specific correction for S.

[0124] By specifying an unsteady criterion value and determining the physical time for unsteady calculations when steady flow does not meet this criterion value, the complete S-characteristic fluctuation cycle can be obtained.

[0125] Specifically, step S2021 above includes:

[0126] Step S2021a: Select criterion.

[0127] Step S2021b: Select at least one criterion and specify the non-steadyness determination value.

[0128] In this embodiment of the invention, the selection criteria include the residual levels of all grids, the residual pressure difference between inlet and outlet, the output residual, the efficiency residual, and the velocity residual at a specified point in the bladeless region of the flow field. The specified point is selected in the bladeless region because the instability of the S-characteristics mainly occurs in the bladeless region. Even if other factors can produce unsteadiness, they will not significantly affect the S-characteristics and do not need to be considered.

[0129] Choose one or more of the above criteria for combined use and specify the judgment value, i.e., the value at which the criterion is considered to indicate significant non-stationarity of the calculation example. It is recommended that the residual level of the inlet and outlet pressure difference be below 10 during periodic fluctuations. -4 When the value decreases monotonically, it is recommended to keep it below 10. -5 The residual level of the entire grid is one order of magnitude more lenient than the residual level of the inlet and outlet pressure difference; the residual levels of output and efficiency are one to two orders of magnitude more lenient than the residual levels of the inlet and outlet pressure difference; and the residual level of velocity at a specified point is two orders of magnitude more lenient than the residual level of the inlet and outlet pressure difference.

[0130] Specifically, step S2022 above includes:

[0131] Step S2022a: Determine the physical time for unsteady calculations.

[0132] In this embodiment of the invention, the physical time length of the unsteady calculation should ensure that the complete S-characteristic fluctuation cycle can be obtained. Generally, the calculation length should be higher than 5 wheel rotation cycles.

[0133] The time step for unsteady calculations should be sufficient to plot the pressure pulsation waveform generated by dynamic-static interference. It is recommended that the maximum value of the simulation time step be determined as follows:

[0134] The static-dynamic interference frequency n in the stationary coordinate system can be calculated using the following formula. fsi(Unit: rpm):

[0135]

[0136] Where, k, m∈N + Z b This refers to the number of leaves.

[0137] For the smallest n that satisfies this equation fsi To accurately describe a sinusoidal waveform, each cycle should have at least 16 time steps, meaning the time intervals must satisfy the following formula:

[0138]

[0139] Specifically, such as Figure 2 As shown, the correction methods include zero-order correction, first-order correction, and second-order correction.

[0140] Specifically, step S2023 above includes:

[0141] Step S2023a: For the unsteady flow when the unit is operating in region S, a zero-order correction is adopted.

[0142] Step S2023b: To address the interference of head fluctuations on the calculation conditions, a first-order correction is adopted.

[0143] Step S2023c involves employing a second-order correction to address the coupled fluctuations in head and flow rate.

[0144] In this embodiment of the invention, the zero-order correction considers the unsteadiness of the flow when the unit operates in region S. Since the head H fluctuates, the calculated unit parameter should be averaged: either the average value or root mean square of the unsteady head H can be used directly to calculate the unit parameter, or the unit parameter can be calculated first and then averaged. The calculation formula is as follows:

[0145]

[0146] or,

[0147]

[0148] like Figure 3 As shown, according to Jensen's inequality, the second method yields a higher unit rotational speed than the first method. (The last sentence appears to be incomplete and possibly refers to a different method, so it's left as is.) 11 Taking the turbine's directional S-characteristics near 50 as an example, when the head fluctuation level reaches 0.4 times the head, the unit speed increases by 2%, and the greater the inlet and outlet pressure difference pulsation, the more significant this increase is.

[0149] In practical applications, the corresponding zero-order correction method should be selected according to the unit rotational speed calculation method used in the experiment. That is, a choice should be made between "calculate the average head first, then calculate the unit parameter" and "calculate the unit parameter first, then calculate the average unit parameter." The simulation should be consistent with the experiment. Offline analysis generally uses the former method, while real-time analysis generally uses the latter method.

[0150] Considering the interference of head fluctuations (H) on the calculation conditions, a first-order correction method is adopted. When H rises, it is equivalent to the operating point shifting to the left along the characteristic curve; when H falls, it is equivalent to the operating point shifting to the right along the characteristic curve. Based on the fluctuation range of H, the curve segment covered by the H fluctuation is obtained from the characteristic curve. Using this curve segment, the HQ mapping relationship can be obtained. Based on the probability distribution X(Q) of H, the probability distribution of Q and the probability distribution of the unit parameter X(n) are mapped to obtain... 11 ), X(Q) 11 Then, a zeroth-order correction method is chosen to calculate the mathematical expectation, i.e.:

[0151]

[0152] or,

[0153] n 11 =E(X(n) 11 ))

[0154] Q 11 =E(X(Q) 11 ))

[0155] Considering the coupled fluctuations of head H and flow rate Q, a second-order correction method is adopted. The second-order correction process is as follows: Figure 4 As shown, in a small region near a certain operating point of a rotating hydraulic machine, H and Q exhibit a fluctuation pattern with essentially the same phase. When both rise, it is equivalent to the operating point moving to the upper left outside the characteristic curve; when they fall, it is equivalent to moving to the lower right outside the curve. However, the first-order correction method does not satisfy this pattern because it directly provides the probability distribution of Q based on the steady-state calculation results and the probability distribution of H, without considering the reaction of Q changes to H. Furthermore, the volatility of H is highly sensitive to the volatility of Q, meaning that slight Q fluctuations can produce strong H fluctuations. The core purpose of the second-order correction method is to provide a calculation method for the reaction of Q to H. Based on this method, more iterations of H and Q fluctuations can be performed.

[0156] First, the H time-domain signal is obtained from the unsteady calculation results. Then, the HQ mapping relationship obtained by the first-order correction method is used to obtain the Q time-domain signal. The fixed inlet flow boundary condition of the example is replaced with the Q time-domain signal, and an unsteady calculation is performed to obtain a new H time-domain signal. The average of the unit parameters is calculated using the Q time-domain signal and the new H time-domain signal. Here, the second zero-order correction method must be used because the first method ignores the phase difference between H and Q, causing the second-order correction to almost degenerate into a first-order correction. If repeated iterations are required, a first-order correction is performed using the new H time-domain signal to obtain a new Q time-domain signal, and then another unsteady calculation is performed to complete one cycle.

[0157] Step S203: Redraw the characteristic curve using the corrected data points.

[0158] Please see details Figure 1 Step S103 of the illustrated embodiment will not be described again here.

[0159] The characteristic curve simulation method based on S-region unsteady CFD correction provided in this embodiment considers the unsteadiness of the flow when the unit is operating in the S region. It adopts a zero-order correction method to compensate for the influence of flow fluctuations, considers the interference of head fluctuations on the calculation conditions, adopts a first-order correction to reduce the interference of head fluctuations, and considers the coupled fluctuations of head and flow rate to adopt a second-order correction, so as to provide a more reliable simulation basis.

[0160] As a specific application embodiment of the present invention, it is assumed that a water pump turbine has a rated head H = 30m and a unit rotational speed n under rated operating conditions. 11 =50. Implementation steps (some data are hypothetical) are as follows:

[0161] (1) Specify the guide vane angle range as 1° to 30°, with an interval of 1°;

[0162] (2) Calculate the rated operating condition opening (assuming guide vane angle = 24°) flow rate as -0.3Q. r ~1.1Q r The steady-state calculation results, after removing the results with negative head, yield the coefficient λ. 100％，min =-0.1;

[0163] (3) Calculate the flow rate as -0.3Q under 35% load condition (assuming guide vane angle = 10°). r ~1.1Q r The steady-state calculation results, after removing the results with negative head, yield the coefficient λ. 35％，min =-0.1;

[0164] (4) Specify n 11，min =5. Use 0.53Q in steps (2) and (3) r~1.1Q r The calculation results are fitted with an exponential function to obtain the fitting relationship in H-λ, and n is then used as the setpoint for the function. 11，min Substituting λ max The calculation formula is then used to obtain λ. 100％，max =5 and λ 35％，max =1;

[0165] (5) Specify the flow inlet for calculating any guide vane angle. For the example with a guide vane angle of k°, divide the λ range into 20 equal parts between (k-18) / 70 and (2k-18) / 7, and densify the flow near 0.

[0166] (6) For all guide vane angles and all flow points, perform steady-state calculations, and take the final head after convergence or the average head of the last 5 fluctuation cycles before convergence as the final head H. Calculate the unit parameters and plot Q for each guide vane angle. 11 -n 11 curve;

[0167] (7) Specify the unsteady criterion: head residuals, select all head residuals > 10. -4 The example performs unsteady calculations, with a physical duration of 300 / n. r seconds, time step is 1 / 16n fsi Obtain the head-time curve;

[0168] (8) Take the average value of the head or unit parameter as the final result to achieve first-order correction. Alternatively, obtain the curve range covered by the head fluctuation on the steady characteristic curve, calculate the head, flow rate and unit parameter to achieve first-order correction. Alternatively, based on this, give the fluctuation inlet flow rate boundary condition to obtain a new head-time curve, and then perform zero-order correction to achieve second-order correction;

[0169] (9) Using the corrected data points, the characteristic curve is redrawn to obtain a characteristic curve that is closer to the experimental method. The redrawn specific curve is as follows: Figure 5 As shown.

[0170] This embodiment also provides a characteristic curve simulation device based on S-region unsteady CFD correction. This device is used to implement the above embodiments and preferred embodiments, and details already described will not be repeated. As used below, the term "module" can be a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0171] This embodiment provides a characteristic curve simulation device based on S-region unsteady CFD correction, such as... Figure 6 As shown, it includes:

[0172] The unsteady calculation module 601 is used to perform CFD steady-state calculations on different guide vane openings to obtain the characteristic curves of the pump-turbine unit.

[0173] The correction module 602 is used to introduce unsteady calculations into the S region and correct some steady calculation data points.

[0174] The redrawing module 603 is used to redraw the characteristic curve using the corrected data points.

[0175] In some alternative implementations, the unsteady calculation module 601 includes:

[0176] The setting unit is used to set the inlet flow boundary conditions and the uniform pressure outlet boundary conditions for each guide vane opening.

[0177] The calculation unit is used to perform CFD steady flow calculations for all boundary condition combinations for all guide vane angles, and obtain head data for each working condition.

[0178] The plotting unit is used to calculate the unit parameters for each operating condition based on head and flow data, and to plot the characteristic curves of each guide vane opening.

[0179] In some optional implementations, the setting unit includes:

[0180] The acquisition sub-unit is used to obtain the approximate flow distribution range at different guide vane openings and different heads.

[0181] The limiting subunit is used to limit the lower limit of flow for all openings.

[0182] The extended sub-unit is used to extend the flow limit for all openings.

[0183] The sub-unit is determined to determine the inlet flow rate of the water pump in the direction of travel.

[0184] In some alternative implementations, the computing unit includes:

[0185] The first judgment subunit is used to determine whether the steady-state calculation has converged based on the residual convergence criterion of the head.

[0186] The first determining sub-unit is used to determine the head in the calculation result of the last iteration step as the final head if the steady-state calculation converges.

[0187] The second judgment subunit is used to determine whether the head exhibits periodic changes if the steady-state calculation does not converge.

[0188] The second determining sub-unit is used to determine the final head by averaging the head over a specific fluctuation period if the head changes periodically.

[0189] The sub-unit is improved to increase the upper limit of the iteration step if the head changes monotonically, and continue the calculation until the preset conditions are met.

[0190] In some alternative implementations, the correction module 602 includes:

[0191] The specified unit is used to specify the unsteady determination value.

[0192] The physical time calculation unit is used to continue unsteady calculations and calculate a certain physical time if the steady flow cannot meet the unsteady determination value.

[0193] The correction unit is used to revise the S-characteristics by utilizing the fluctuation characteristics of the water head.

[0194] In some optional implementations, the correction unit further includes:

[0195] The first correction sub-unit is used to apply zero-order correction to address the unsteadiness of the flow when the unit is operating in the S region.

[0196] The second correction sub-unit is used to address the interference of head fluctuations on the calculation conditions by employing first-order correction.

[0197] The third correction sub-unit is used to address the coupled fluctuations in head and flow rate, employing a second-order correction.

[0198] Further functional descriptions of the above modules and units are the same as those in the corresponding embodiments described above, and will not be repeated here.

[0199] In this embodiment, the characteristic curve simulation device based on S-region unsteady CFD correction is presented in the form of functional units. Here, a unit refers to an ASIC (Application Specific Integrated Circuit) circuit, a processor and memory that execute one or more software or fixed programs, and / or other devices that can provide the above functions.

[0200] This invention also provides a computer device having the above-described features. Figure 6 The characteristic curve simulation device shown is based on S-region unsteady CFD correction.

[0201] Please see Figure 7 , Figure 7 This is a schematic diagram of the structure of a computer device provided in an optional embodiment of the present invention, such as... Figure 7As shown, the computer device includes one or more processors 10, memory 20, and interfaces for connecting the components, including high-speed interfaces and low-speed interfaces. The components communicate with each other via different buses and can be mounted on a common motherboard or otherwise installed as needed. The processors can process instructions executed within the computer device, including instructions stored in or on memory to display graphical information of a GUI on external input / output devices (such as display devices coupled to the interfaces). In some alternative implementations, multiple processors and / or multiple buses can be used with multiple memories and multiple memory modules, if desired. Similarly, multiple computer devices can be connected, each providing some of the necessary operations (e.g., as a server array, a group of blade servers, or a multiprocessor system). Figure 7 Take a processor 10 as an example.

[0202] Processor 10 may be a central processing unit, a network processor, or a combination thereof. Processor 10 may further include a hardware chip. The hardware chip may be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a combination thereof. The programmable logic device may be a complex programmable logic device (CAMP), a field-programmable gate array (FPGA), a general-purpose array logic (GDA), or any combination thereof.

[0203] The memory 20 stores instructions executable by at least one processor 10 to cause at least one processor 10 to perform the method shown in the above embodiments.

[0204] The memory 20 may include a program storage area and a data storage area. The program storage area may store the operating system and applications required for at least one function; the data storage area may store data created based on the use of the computer device. Furthermore, the memory 20 may include high-speed random access memory and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some alternative embodiments, the memory 20 may optionally include memory remotely located relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0205] The memory 20 may include volatile memory, such as random access memory; the memory may also include non-volatile memory, such as flash memory, hard disk or solid-state drive; the memory 20 may also include a combination of the above types of memory.

[0206] The computer device also includes an input device 30 and an output device 40. The processor 10, memory 20, input device 30, and output device 40 can be connected via a bus or other means. Figure 7 Taking the example of a connection between China and Israel via a bus.

[0207] Input device 30 can receive input numerical or character information, and generate key signal inputs related to user settings and function control of the computer device, such as a touch screen. Output device 40 may include a display device, etc.

[0208] This invention also provides a computer-readable storage medium. The methods described above according to embodiments of the invention can be implemented in hardware or firmware, or implemented as computer code that can be recorded on a storage medium, or implemented as computer code downloaded via a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that computers, processors, microprocessor controllers, or programmable hardware include storage components capable of storing or receiving software or computer code, which, when accessed and executed by the computer, processor, or hardware, implements the methods shown in the above embodiments.

[0209] A portion of this invention can be applied as a computer program product, such as computer program instructions, which, when executed by a computer, can invoke or provide the methods and / or technical solutions according to the invention through the operation of the computer. Those skilled in the art will understand that the forms in which computer program instructions exist in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways in which computer program instructions are executed by a computer include, but are not limited to: the computer directly executing the instructions, or the computer compiling the instructions and then executing the corresponding compiled program, or the computer reading and executing the instructions, or the computer reading and installing the instructions and then executing the corresponding installed program. Here, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible to a computer.

[0210] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope of this application.

Claims

1. A characteristic curve simulation method based on S-region unsteady CFD correction, characterized in that, The method includes: CFD steady-state calculations were performed for different guide vane openings to obtain the characteristic curves of the pump-turbine unit; Unsteady calculations are introduced into region S, and some steady calculation data points are corrected. The characteristic curve is redrawn using the corrected data points.

2. The method according to claim 1, characterized in that, The step of performing CFD steady-state calculations on different guide vane openings to obtain the characteristic curves of the pump-turbine unit includes: For each guide vane opening, set inlet flow boundary conditions and set uniform pressure outlet boundary conditions; CFD steady flow calculations were performed for all boundary condition combinations for all guide vane angles to obtain head data for each working condition. Based on the head and flow data, calculate the unit parameters for each operating condition and plot the characteristic curves for each guide vane opening.

3. The method according to claim 2, characterized in that, The set ingress flow boundary conditions include: To obtain the approximate flow distribution range at different water heads with different guide vane openings; Lower limit of flow rate for all openings; Expand the flow limit for all openings; Determine the inlet flow rate of the water pump.

4. The method according to claim 2, characterized in that, The CFD steady flow calculations are performed for all boundary condition combinations for all guide vane angles to obtain head data for each operating condition, including: Based on the residual convergence criterion of head, determine whether the steady-state calculation has converged; If the steady-state calculation converges, then the head in the calculation result of the last iteration step is determined as the final head. If the steady-state calculation does not converge, then determine whether the head exhibits periodic changes. If the water head changes periodically, the average water head during a specific fluctuation period is taken as the final water head. If the water head changes monotonically, increase the upper limit of the iteration step and continue the calculation until the preset conditions are met.

5. The method according to claim 1, characterized in that, The introduction of unsteady calculations into region S and the correction of some steady-calculation data points include: Specify the non-steadyness determination value; If the steady flow cannot meet the unsteady condition criteria, then continue the unsteady calculation for a certain physical time. The S-characteristics are corrected by utilizing the fluctuation characteristics of the water head.

6. The method according to claim 5, characterized in that, The correction methods include zero-order correction, first-order correction, and second-order correction.

7. The method according to claim 6, characterized in that, The modification of the S-characteristics includes: To address the unsteady flow characteristics when the unit operates in the S region, a zero-order correction is employed. To address the interference of head fluctuations on the calculation conditions, a first-order correction is adopted; A second-order correction is adopted to address the coupled fluctuations in head and flow rate.

8. A characteristic curve simulation device based on S-region unsteady CFD correction, characterized in that, The device includes: The unsteady calculation module is used to perform CFD steady-state calculations on different guide vane openings to obtain the characteristic curves of the pump-turbine unit. The correction module is used to introduce unsteady calculations in the S region and correct some steady calculation data points. The redraw module is used to redraw the characteristic curve using the corrected data points.

9. A computer device, characterized in that, include: The system includes a memory and a processor, which are interconnected. The memory stores computer instructions, and the processor executes the computer instructions to perform the characteristic curve simulation method based on S-region unsteady CFD correction as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing the computer to execute the characteristic curve simulation method based on S-region unsteady CFD correction as described in any one of claims 1 to 7.

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