Method for adjusting installation elevation of pump-turbine unit of pumped storage power station based on double-end coupled simulation

Abstract

The present application belongs to the technical field of pumped storage power station, and discloses a pumped storage power station pump-turbine unit installation elevation adjustment method based on double-end coupling simulation, which comprises the following steps: establishing a full-flow passage three-dimensional model of the pumped storage power station at a certain installation elevation; determining an upstream double-end coupling section and a downstream double-end coupling section; dividing grid units, and performing load rejection transient process calculation; solving the pump-turbine, the upstream and downstream water delivery systems, the upstream and downstream double-end coupling sections; and performing total step iteration calculation, and determining whether the tailrace pipe water column separation occurs according to the water vapor volume inside the tailrace pipe and the upward axial force on the runner, and further determining whether to adjust the installation elevation of the pump-turbine in the pumped storage power station. The present application can determine whether to adjust the installation elevation of the pump-turbine in the pumped storage power station through double-end coupling simulation, and provides a reference for the installation elevation design of the pumped storage power station pump-turbine unit.

Description

Technical Field

[0001] This invention belongs to the technical field of pumped storage power stations, specifically relating to a method for adjusting the installation elevation of pump-turbine units in pumped storage power stations based on dual-end coupling simulation. Background Technology

[0002] Currently, pumped storage power stations are developing towards high head and large capacity, but high head means higher risks. This is because the start-up and shutdown of the pump-turbine unit, shutdowns due to emergency conditions (load shedding, runaway), and normal shutdowns can all cause drastic changes in flow rate and pressure. When the pressure drops to the vaporization pressure and remains there for a period of time, the liquid vaporizes to form cavitation bubbles. These cavitation bubbles flow with the liquid and may even develop, aggregate, and grow to occupy the entire flow cross-section, causing the liquid column to break and resulting in water column separation, which in turn induces a strong backflow hammer. Since the re-merging of the separated water column leads to a huge pressure rise, this may cause the rotating parts of the unit to lift (i.e., turbine lift), resulting in damage to the unit. Currently, to prevent water column separation in engineering projects, empirical formulas are used. These formulas superimpose the water hammer wave pressure at the tailrace inlet calculated using a one-dimensional transient process with the estimated pulsating pressure as the control condition for tailrace water column separation. However, these overly stringent water column separation constraints have led to a reduction in the installation elevation of high-head pump-turbine units to -100m or even lower, consequently lowering the underground powerhouse. This significantly increases construction difficulty and project investment. Therefore, empirical formulas cannot accurately determine the installation elevation of pump-turbine units, necessitating the development of a more precise method for adjusting the unit's installation elevation.

[0003] Computational Fluid Dynamics (CFD) simulation is a commonly used analytical method for solving the above problems. However, since water column separation involves two phases—liquid and vapor—and mass exchange between them, for high-head pumped storage power stations with surge tanks, the flow inside the surge tank involves two phases—air and liquid water. Current CFD numerical simulation methods based on one-dimensional and three-dimensional coupling calculate the pump-turbine in three dimensions, while calculating the pipes and surge tank in one dimension. The surge tank impedance orifice is determined using empirical coefficients. This method cannot simultaneously and accurately simulate both the water column separation in the tailrace and the free surface of the surge tank, thus failing to provide reliable guidance for adjusting the installation elevation of the pump-turbine units during the design of pumped storage power stations. Therefore, it is necessary to improve the CFD simulation method to provide a reference for accurately determining the installation elevation of the pump-turbine units in pumped storage power stations. Summary of the Invention

[0004] This invention addresses the aforementioned engineering problems by providing a method for adjusting the installation elevation of pump-turbine units in pumped-storage power stations based on dual-end coupling simulation. This method can determine whether water column separation has occurred in the tailrace tube based on the volume of water vapor inside the tailrace tube and the upward axial force on the runner during the load shedding process of the pump-turbine, thereby determining whether to adjust the installation elevation of the pump-turbine in the pumped-storage power station. This provides a reference for the design of the installation elevation of pump-turbine units in pumped-storage power stations.

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

[0006] A method for adjusting the installation elevation of a pump-turbine unit in a pumped storage power station based on two-end coupling simulation includes the following steps:

[0007] a. Establish a three-dimensional model of the entire flow channel of a pumped storage power station at a certain installation elevation. The three-dimensional model of the entire flow channel includes the upstream water conveyance system, the pump turbine and the downstream water conveyance system.

[0008] b. Select the upstream boundary section and the downstream boundary section to determine the upstream double-end coupling section and the downstream double-end coupling section;

[0009] c. Divide the upstream water conveyance system, the upstream double-end coupling section, the pump turbine, the downstream double-end coupling section, and the downstream water conveyance system into grid cells respectively. The overlapping parts of the upstream water conveyance system and the pump turbine with the upstream double-end coupling section, and the overlapping parts of the pump turbine and the downstream water conveyance system with the downstream double-end coupling section, have the same grid cells. Then import them into CFD software to calculate the load shedding transition process.

[0010] d. The pump-turbine is solved using the k-epsilon turbulence model and the Mixture cavitation model. Flow field boundary conditions are set, and the solution converges over the entire region to obtain the flow field information of liquid water and water vapor phases in each volume grid cell of the pump-turbine region during the load shedding transition, as well as the mass and momentum exchange between the two phases.

[0011] e. Both the upstream and downstream water conveyance systems are solved using the k-epsilon turbulence model and the VOF free surface model. Flow field boundary conditions are set, and the solution converges over the entire region to obtain the flow field information of liquid water and air phases in each volume grid cell of the upstream and downstream water conveyance systems during the load shedding transition, as well as the momentum exchange between the two phases.

[0012] f. The k-epsilon turbulence model is used for the upstream and downstream double-ended coupling sections. The calculation results of the volume grid cells of the upstream water conveyance system and the upstream double-ended coupling section, and the downstream water conveyance system and the downstream double-ended coupling section are used as input conditions to perform iterative solution of the single-phase liquid water flow in the upstream and downstream double-ended coupling sections, so as to obtain the flow field information of the surface grid cells of the upstream and downstream interface sections.

[0013] g. With a total duration of 50s and a time step of 0.001s, repeat steps d to f. Use the flow field information of the surface grid cells of the upstream and downstream junction sections obtained in step f as the flow field boundary conditions of the pump turbine, the upstream water conveyance system, and the downstream water conveyance system for the next time step, respectively. Perform iterative calculations of the flow field information of the volume grid cells in the pump turbine area, the upstream water conveyance system and the entire upstream water conveyance system, and the upstream double-end coupling section and the downstream double-end coupling section for the next time step. At the same time, record the water vapor volume inside the tailrace pipe and the upward axial force on the runner obtained in each calculation.

[0014] h. Based on the volume of water vapor inside the tailrace pipe and the upward axial force on the runner, determine whether tailrace pipe water column separation has occurred, and then determine whether to adjust the installation elevation of the pump turbine in the pumped storage power station.

[0015] In one technical solution, the upstream boundary section in step b is the section between the upstream water conveyance system and the water pump turbine where cavitation does not occur, and the downstream boundary section is the section between the water pump turbine and the downstream water conveyance system where cavitation does not occur. A pipe with a length of several times the pipe diameter before and after the upstream boundary section is selected as the upstream double-end coupling section, and a pipe with a length of several times the pipe diameter before and after the downstream boundary section is selected as the downstream double-end coupling section.

[0016] In one technical solution, a pipe with a length of five times the pipe diameter before and after the upstream boundary fracture is selected as the upstream double-end coupling section, and a pipe with a length of five times the pipe diameter before and after the downstream boundary fracture is selected as the downstream double-end coupling section.

[0017] In one technical solution, the grid cell is a hexahedron or a triangular prism, and the maximum side length of the grid cell does not exceed 5% of the cross-sectional diameter.

[0018] In one technical solution, step h specifically includes the following steps:

[0019] When the maximum volume of water vapor inside the tailrace pipe, V, is greater than 0.5 m³. 3 And the maximum upward axial force F Z If the weight G of the rotating parts of the pump-turbine unit is applied for more than 0.2 seconds, it is determined that the tailrace water column has separated, and the installation elevation of the pump-turbine unit needs to be lowered.

[0020] When the maximum volume of water vapor inside the tailrace pipe, V, is greater than 0.5 m³. 3 And the maximum upward axial force F Z If the gravity G of the rotating parts of the pump-turbine unit is applied for less than 0.2 seconds, it is determined that the tailrace water column has separated, but there is no need to adjust the installation elevation of the pump-turbine unit.

[0021] When the maximum volume of water vapor V < 0.5m 3 And the maximum upward axial force F Z If the weight G of the rotating components of the pump-turbine unit is less than the weight G, it is determined that no tailrace water column separation has occurred, and the installation elevation of the pump-turbine unit needs to be increased.

[0022] In one technical solution, the reduction of the installation elevation of the water pump turbine unit is performed according to the following formula: ΔH=(p1–p2) / (t2–t1)×(t3–t2) / ρ / g, where: ρ is the density of liquid water, kg / m³ 3 g is the acceleration due to gravity, in m / s². 2 ; t1 is the initial time of water column separation; p1 is the pressure at the inlet section of the tailrace pipe at the initial time of water column separation, Pa; t2 is the time when water column separation is fully formed; p2 is the pressure at the inlet section of the tailrace pipe at the time when water column separation is fully formed, Pa; t3 is the time when water column separation collapses.

[0023] In one technical solution, the installation elevation of the booster pump turbine unit is determined according to the following formula: ΔH=(p min -p v ) / ρ / g, where: ρ is the density of liquid water, kg / m³ 3 g is the acceleration due to gravity, in m / s². 2 ;p min The minimum pressure within the pump-turbine flow channel, in Pa; p v ρ is the saturated water vapor pressure, in Pa.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention employs double-end coupling, fully considering the two-phase problem of liquid water and air in the upstream and downstream surge tanks during the pump-turbine load shedding process. Through data transfer from volume grid cells to surface grid cells and then back to volume grid cells, iterative calculations of flow field information in the volume grid cells within the pump-turbine area, the upstream water conveyance system and the entire upstream water conveyance system, and the upstream and downstream double-end coupling sections are performed over the total duration. Based on the volume of water vapor inside the tailrace and the upward axial force on the runner during the pump-turbine load shedding transition, it can be determined whether tailrace column separation has occurred, and thus determine whether the installation elevation of the pump-turbine in the pumped storage power station needs to be adjusted, providing a reference for the design of the installation elevation of the pump-turbine unit in the pumped storage power station. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall computational domain of the transition process of the present invention.

[0027] Figure 2 This is a side view of a three-dimensional model of the downstream double-ended coupling section of the present invention.

[0028] Figure 3 This is a three-dimensional model diagram of the downstream double-ended coupling section of the present invention.

[0029] Figure 4 This is a flowchart of the calculation process for the load shedding transition in this invention.

[0030] Figure 5 This is a schematic diagram of the data transmission of the body grid unit from the pump turbine area and the downstream water conveyance system (tailrace pressure regulating chamber area) of the present invention to the downstream double-end coupling section.

[0031] Figure 6 This is a schematic diagram of the data transfer of the surface grid unit from the downstream double-end coupling section to the water pump turbine area and the downstream water conveyance system (tailrace pressure regulating chamber area) of the present invention.

[0032] Figure 7 These are the calculation results, where: (a)-(c) are schematic diagrams of water column separation in the tailrace pipe; (d)-(f) are schematic diagrams of the lifting evaluation; and (g)-(i) are schematic diagrams of the inlet pressure of the tailrace pipe. Detailed Implementation

[0033] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the test methods in the following embodiments are conventional methods.

[0034] Example 1

[0035] A method for adjusting the installation elevation of pump-turbine units in pumped storage power stations based on two-end coupling simulation includes the following steps:

[0036] a. Establish a three-dimensional model of the entire flow channel of a pumped storage power station at a certain installation elevation, such as... Figure 1 As shown, the three-dimensional model of the entire flow channel includes the upstream water conveyance system, the water pump turbine, and the downstream water conveyance system.

[0037] b. Select the upstream and downstream boundary sections to determine the upstream and downstream double-end coupling sections. Specifically: the upstream boundary section is the section between the upstream water conveyance system and the pump turbine where cavitation does not occur; the downstream boundary section is the section between the pump turbine and the downstream water conveyance system where cavitation does not occur. Select a pipe section with a length of five times the pipe diameter before and after the upstream boundary section as the upstream double-end coupling section; select a pipe section with a length of five times the pipe diameter before and after the downstream boundary section as the downstream double-end coupling section (e.g., ...). Figure 2 and Figure 3 (As shown).

[0038] c. Using hexahedrons, mesh elements are divided for the upstream water conveyance system, the upstream double-end coupling section, the pump-turbine, the downstream double-end coupling section, and the downstream water conveyance system. The maximum side length of each mesh element is 5% of the cross-sectional diameter. The overlapping portions of the upstream water conveyance system and the pump-turbine with the upstream double-end coupling section, and the overlapping portions of the pump-turbine and the downstream water conveyance system with the downstream double-end coupling section, all have the same mesh elements. These are then imported into CFD software for load shedding transient process calculations (e.g., ...). Figure 4 (As shown).

[0039] d. The pump-turbine is solved using the k-epsilon turbulence model and the Mixture cavitation model. Flow field boundary conditions are set, and the solution converges over the entire region. The flow field information (such as velocity and pressure) of liquid water and water vapor in each volume grid cell of the pump-turbine region during the load shedding transition is obtained, as well as the mass and momentum exchange between the two phases.

[0040] e. Both the upstream and downstream water conveyance systems are solved using the k-epsilon turbulence model and the VOF free surface model. Flow field boundary conditions are set, and the solution converges across the entire region. This yields the flow field information (such as velocity and pressure) of the liquid water and air phases in each volume grid cell of the upstream and downstream water conveyance systems during the load shedding transition, as well as the momentum exchange between the two phases.

[0041] f. The k-epsilon turbulence model is used for both the upstream and downstream double-ended coupling sections. The calculation results of the overlapping volume grid elements of the upstream water conveyance system and the upstream and downstream double-ended coupling sections are used as input conditions to iteratively solve for the single-phase liquid water flow in both sections. This yields the flow field information (such as velocity and pressure) of the surface grid elements at the upstream and downstream interface sections. Figure 5(As shown).

[0042] g. With a total duration of 50 seconds and a time step of 0.001 seconds, repeat steps d to f. Use the flow field information of the surface grid cells of the upstream and downstream junction sections obtained in step f as the flow field boundary conditions of the pump turbine, upstream water conveyance system, and downstream water conveyance system for the next time step, respectively (e.g., Figure 6 As shown in the figure, the flow field information of the volume grid elements in the pump-turbine area, the upstream water conveyance system and the entire upstream water conveyance system, the upstream double-end coupling section and the downstream double-end coupling section are iteratively calculated for the next time step. At the same time, the volume of water vapor inside the tailrace pipe and the upward axial force on the runner are recorded at each calculation. The calculation results are as follows. Figure 7 As shown.

[0043] h. Based on the volume of water vapor inside the tailrace and the upward axial force on the turbine runner, determine whether tailrace column separation has occurred, and then determine whether to adjust the installation elevation of the pump turbine in the pumped storage power station. This includes the following steps:

[0044] When the maximum volume of water vapor inside the tailrace pipe, V, is greater than 0.5 m³. 3 And the maximum upward axial force F Z If the weight G of the rotating components of the pump-turbine unit is applied for more than 0.2 seconds, it is determined that water column separation has occurred in the tailrace pipe, and the installation elevation of the pump-turbine unit needs to be lowered. The lowering of the installation elevation of the pump-turbine unit is carried out according to the following formula: ΔH=(p1–p2) / (t2–t1)×(t3–t2) / ρ / g, where: ρ is the density of liquid water, kg / m³ 3 g is the acceleration due to gravity, in m / s². 2 ; t1 is the initial time of water column separation; p1 is the pressure at the inlet section of the tailrace pipe at the initial time of water column separation, Pa; t2 is the time when water column separation is fully formed; p2 is the pressure at the inlet section of the tailrace pipe at the time when water column separation is fully formed, Pa; t3 is the time when water column separation collapses.

[0045] When the maximum volume of water vapor inside the tailrace pipe, V, is greater than 0.5 m³. 3 And the maximum upward axial force F Z If the gravity G of the rotating parts of the pump-turbine unit is applied for less than 0.2 seconds, it is determined that the tailrace water column has separated, but there is no need to adjust the installation elevation of the pump-turbine unit.

[0046] When the maximum volume of water vapor V < 0.5m 3 And the maximum upward axial force F ZIf the weight G of the rotating components of the pump-turbine unit is less than the weight G, it is determined that no tailrace column separation has occurred, and the installation elevation of the pump-turbine unit needs to be raised. The elevation of the pump-turbine unit is raised according to the following formula: ΔH=(p min -p v ) / ρ / g, where: ρ is the density of liquid water, kg / m³ 3 g is the acceleration due to gravity, in m / s². 2 ;p min The minimum pressure within the pump-turbine flow channel, in Pa; p v ρ is the saturated water vapor pressure, in Pa.

[0047] i. After adjusting the installation elevation, repeat steps a to h to verify whether the adjusted installation elevation meets the requirements of preventing water column separation and machine lifting.

[0048] The embodiments described above are merely preferred embodiments of the present invention and are only used to explain the present invention. They are not intended to limit the scope of the present invention. For those skilled in the art, other implementation methods can be easily made by substitution or modification based on the technical content disclosed in this specification. Therefore, all changes and improvements made on the principle of the present invention should be included within the scope of the patent application of the present invention.

Claims

1. A method for adjusting the installation elevation of a pump-turbine unit in a pumped-storage power station based on two-end coupling simulation, characterized in that, Includes the following steps: a. Establish a three-dimensional model of the entire flow channel of a pumped storage power station at a certain installation elevation. The three-dimensional model of the entire flow channel includes the upstream water conveyance system, the pump turbine and the downstream water conveyance system. b. Select the upstream boundary section and the downstream boundary section to determine the upstream double-end coupling section and the downstream double-end coupling section; c. Divide the upstream water conveyance system, the upstream double-end coupling section, the pump turbine, the downstream double-end coupling section, and the downstream water conveyance system into grid cells respectively. The overlapping parts of the upstream water conveyance system and the pump turbine with the upstream double-end coupling section, and the overlapping parts of the pump turbine and the downstream water conveyance system with the downstream double-end coupling section, have the same grid cells. Then import them into CFD software to calculate the load shedding transition process. d. The pump-turbine is solved using the k-epsilon turbulence model and the Mixture cavitation model. Flow field boundary conditions are set, and the solution converges over the entire region to obtain the flow field information of liquid water and water vapor phases in each volume grid cell of the pump-turbine region during the load shedding transition, as well as the mass and momentum exchange between the two phases. e. Both the upstream and downstream water conveyance systems are solved using the k-epsilon turbulence model and the VOF free surface model. Flow field boundary conditions are set, and the solution converges over the entire region to obtain the flow field information of liquid water and air phases in each volume grid cell of the upstream and downstream water conveyance systems during the load shedding transition, as well as the momentum exchange between the two phases. f. The k-epsilon turbulence model is used for the upstream and downstream double-ended coupling sections. The calculation results of the volume grid cells of the upstream water conveyance system and the upstream double-ended coupling section, and the downstream water conveyance system and the downstream double-ended coupling section are used as input conditions to perform iterative solution of the single-phase liquid water flow in the upstream and downstream double-ended coupling sections, so as to obtain the flow field information of the surface grid cells of the upstream and downstream interface sections. g. With a total duration of 50s and a time step of 0.001s, repeat steps d to f. Use the flow field information of the surface grid cells of the upstream and downstream junction sections obtained in step f as the flow field boundary conditions of the pump turbine, the upstream water conveyance system, and the downstream water conveyance system for the next time step, respectively. Perform iterative calculations of the flow field information of the volume grid cells in the pump turbine area, the upstream water conveyance system and the entire upstream water conveyance system, and the upstream double-end coupling section and the downstream double-end coupling section for the next time step. At the same time, record the water vapor volume inside the tailrace pipe and the upward axial force on the runner obtained in each calculation. h. Based on the volume of water vapor inside the tailrace pipe and the upward axial force on the runner, determine whether tailrace pipe water column separation has occurred, and then determine whether to adjust the installation elevation of the pump turbine in the pumped storage power station.

2. The method for adjusting the installation elevation of the pump-turbine unit in a pumped storage power station based on dual-end coupling simulation according to claim 1, characterized in that, In step b, the upstream boundary section is the section between the upstream water conveyance system and the pump turbine where cavitation does not occur, and the downstream boundary section is the section between the pump turbine and the downstream water conveyance system where cavitation does not occur. A pipe with a length of several times the pipe diameter before and after the upstream boundary section is selected as the upstream double-end coupling section, and a pipe with a length of several times the pipe diameter before and after the downstream boundary section is selected as the downstream double-end coupling section.

3. The method for adjusting the installation elevation of the pump-turbine unit in a pumped storage power station based on dual-end coupling simulation according to claim 2, characterized in that, The pipe with a length of five times the pipe diameter before and after the upstream boundary section is selected as the upstream double-end coupling section, and the pipe with a length of five times the pipe diameter before and after the downstream boundary section is selected as the downstream double-end coupling section.

4. The method for adjusting the installation elevation of the pump-turbine unit in a pumped storage power station based on dual-end coupling simulation according to claim 1, characterized in that, The grid cells are hexahedrons or triangular prisms, and the maximum side length of the grid cells does not exceed 5% of the cross-sectional diameter.

5. The method for adjusting the installation elevation of the pump-turbine unit in a pumped storage power station based on dual-end coupling simulation according to claim 1, characterized in that, Step h specifically includes the following steps: When the maximum volume of water vapor inside the tailrace pipe, V, is greater than 0.5 m³. 3 And the maximum upward axial force F Z If the weight G of the rotating parts of the pump-turbine unit is applied for more than 0.2 seconds, it is determined that the tailrace water column has separated, and the installation elevation of the pump-turbine unit needs to be lowered. When the maximum volume of water vapor inside the tailrace pipe, V, is greater than 0.5 m³. 3 And the maximum upward axial force F Z If the gravity G of the rotating parts of the pump-turbine unit is applied for less than 0.2 seconds, it is determined that the tailrace water column has separated, but there is no need to adjust the installation elevation of the pump-turbine unit. When the maximum volume of water vapor V < 0.5m 3 And the maximum upward axial force F Z If the weight G of the rotating components of the pump-turbine unit is less than the weight G, it is determined that no tailrace water column separation has occurred, and the installation elevation of the pump-turbine unit needs to be increased.

6. The method for adjusting the installation elevation of the pump-turbine unit of a pumped storage power station based on dual-end coupling simulation according to claim 5, characterized in that, The reduction of the installation elevation of the water pump turbine unit is carried out according to the following formula: ΔH=(p1–p2) / (t2–t1)×(t3–t2) / ρ / g, where: ρ is the density of liquid water, kg / m³ 3 g is the acceleration due to gravity, in m / s². 2 ; t1 is the initial time of water column separation; p1 is the pressure at the inlet section of the tailrace pipe at the initial time of water column separation, Pa; t2 is the time when water column separation is fully formed; p2 is the pressure at the inlet section of the tailrace pipe at the time when water column separation is fully formed, Pa; t3 is the time when water column separation collapses.

7. The method for adjusting the installation elevation of the pump-turbine unit of a pumped storage power station based on dual-end coupling simulation according to claim 5, characterized in that, The installation elevation of the booster pump turbine unit is determined according to the following formula: ΔH=(p min -p v ) / ρ / g, where: ρ is the density of liquid water, kg / m³ 3 g is the acceleration due to gravity, in m / s². 2 ;p min The minimum pressure within the pump-turbine flow channel, in Pa; p v ρ is the saturated water vapor pressure, in Pa.

Images