Numerical calculation method and device for transition process of pump turbine and storage medium

Abstract

The invention provides a numerical calculation method and device for the transition process of a pump turbine and a storage medium. The method comprises the following steps: establishing a full-flow-channel numerical calculation model of the pump turbine; the initial torque and the initial rotating speed of the pump turbine under the initial steady-state working condition before the transition process are determined; performing numerical calculation according to the initial torque, the initial rotating speed, a turbulence model of numerical calculation and inlet and outlet boundary conditions; in the numerical calculation process, the rotating speed of the impeller of the pump turbine at the second moment is determined according to the rotating speed of the impeller at the first moment, the resultant moment acting on the impeller at the first moment, the rotational inertia of the impeller and the time step length of numerical calculation; wherein the first moment is before the second moment, the time difference between the first moment and the second moment is a time step length, and the resultant moment acting on the impeller at the first moment is determined according to a numerical calculation result.

Description

Technical Field

[0001] The present application relates to the field of computer numerical simulation calculations, and more specifically, to a numerical calculation method, device, and storage medium for the transient process of a pump-turbine. Background Art

[0002] The pump-turbine is an important component of a pumped-storage power station. During transient processes such as startup and shutdown, sudden load rejection, runaway, and emergency braking, the speed, torque, and other parameters related to the pump-turbine's external characteristics will undergo strong transient changes, making the internal flow field extremely unstable. This can cause transient hydraulic shocks on the unit's exterior or transient motor overloads, as well as vibration and noise, which have a significant impact on the unit's stable operation. Therefore, the study of the flow characteristics and mechanical behavior of the fluid inside the pump-turbine under transient conditions is of great significance for its optimal design, operation control, and fault diagnosis.

[0003] Numerical calculation method is a feasible way to study the transient process of pump turbine. For example, the above process can be numerically calculated by computer simulation software to determine the fluid characteristics and mechanical characteristics in the above transient process.

[0004] In related technologies, the research objects of numerical calculations are generally conventional turbines or vane pumps, rather than pumped-storage pump-turbines, and fixed values ​​are used for the inlet and outlet boundary conditions or obtained through the simultaneous one-dimensional characteristic line method. Both methods simplify the boundary conditions to a certain extent, that is, the conditions of numerical simulation do not match the actual situation, which will affect the accuracy of the external characteristic parameters of the pump-turbine and the internal flow state simulation, resulting in unreliable results of the numerical simulation.

[0005] Therefore, how to improve the accuracy of numerical calculation of the transient law of characteristic parameters of pump-turbine during the transition process and the dynamic characteristics of the internal flow field has become an urgent problem to be solved. Summary of the Invention

[0006] This application mainly provides a numerical calculation method and device, as well as a storage medium, for the transient process of a pump-turbine. The technical solution of this application is implemented as follows:

[0007] In a first aspect, a numerical calculation method for a transient process of a pump-turbine is provided, the method comprising: establishing a full-flow channel numerical calculation model of the pump-turbine; determining the initial torque and initial speed of the pump-turbine under the initial steady-state working condition before the transient process; performing the numerical calculation according to the initial torque and initial speed, the turbulence model of the numerical calculation, and the inlet and outlet boundary conditions; during the numerical calculation process, the speed of the impeller of the pump-turbine at the second moment is determined according to the speed of the impeller at the first moment, the resultant torque acting on the impeller at the first moment, the moment of inertia of the impeller, and the time step of the numerical calculation; wherein, the first moment is before the second moment, the time difference between the first moment and the second moment is the time step, and the resultant torque acting on the impeller at the first moment is determined according to the result of the numerical calculation.

[0008] In the technical solution of the embodiment of the present application, during the numerical calculation process, the speed of the impeller of the pump turbine at the second moment is determined based on the speed of the impeller at the first moment, the resultant torque acting on the impeller at the first moment, the rotational relationship of the impeller, and the time step of the numerical calculation; wherein, before the first moment, the time difference between the first moment and the second moment is the above-mentioned time step, and the resultant torque acting on the impeller at the first moment is determined based on the result of the numerical calculation. Different from the related art in which the motion law of the impeller is predefined before the numerical calculation, in the solution of the present application, the speed of the impeller at each moment is related to the numerical result of the previous moment, that is, the impeller speed is cyclically iterated in the numerical calculation. The change of the impeller speed determined based on this method is more in line with the actual working conditions.

[0009] In some embodiments, the rotational speed of the impeller at the second moment is the sum of the rotational speed of the impeller at the first moment and a first parameter, and the first parameter is the product of the ratio of the resultant torque acting on the impeller at the first moment to the moment of inertia of the impeller and the time step.

[0010] According to the above technical solution, based on the rotational angular momentum balance equation, an iterative calculation method for the impeller speed is determined. The impeller speed determined according to this method is closer to the actual working conditions and can improve the reliability of the numerical calculation results.

[0011] In some embodiments, establishing a numerical calculation model of the entire flow channel of a pump-turbine includes: establishing a three-dimensional model of the pump-turbine; performing grid division on the three-dimensional model with different numbers of grids; performing grid independence verification on models with different numbers of grids to determine the optimal number of grids for the numerical calculation model; and performing grid division on the three-dimensional model according to the optimal number of grids to obtain the numerical calculation model.

[0012] In some embodiments, the pump-turbine includes a volute, an impeller, a guide vane and a tailwater pipe, and the establishment of a numerical calculation model of the entire flow path of the pump-turbine also includes: setting the impeller as a rotating dynamic domain, and setting the volute, the guide vane and the tailwater pipe as a static domain; setting a transient rotor stator at the dynamic and static interface between the rotating dynamic domain and the static domain; and setting the avoidance of each flow-passing component in the pump-turbine to a no-slip boundary.

[0013] In some embodiments, the turbulence model is an SST k-ω model; and the inlet and outlet boundary conditions are that the inlet and outlet of the pump turbine are open pressure and direction.

[0014] In some embodiments, the method further includes: during the numerical calculation, detecting a change in the resultant torque, and stopping the numerical calculation when the resultant torque approaches zero.

[0015] In a second aspect, a numerical calculation device for a water pump turbine runaway transition process is provided, the device comprising: a modeling unit for establishing a numerical calculation model of the entire flow channel of the water pump turbine; a first determination unit for determining the initial torque and initial speed of the water pump turbine under the initial steady-state working condition before the runaway; a numerical calculation unit for performing the numerical calculation based on the initial torque and initial speed, the turbulence model of the numerical calculation, and the inlet and outlet boundary conditions; during the numerical calculation process, the speed of the impeller of the water pump turbine at the second moment is determined based on the speed of the impeller at the first moment, the resultant torque acting on the impeller at the first moment, the moment of inertia of the impeller, and the time step of the numerical calculation; wherein, the first moment is before the second moment, the time difference between the first moment and the second moment is the time step, and the resultant torque acting on the impeller at the first moment is determined based on the result of the numerical calculation.

[0016] In some embodiments, the rotational speed of the impeller at the second moment is the sum of the rotational speed of the impeller at the first moment and a first parameter, and the first parameter is the product of the ratio of the resultant torque acting on the impeller at the first moment to the moment of inertia of the impeller and the time step.

[0017] In some embodiments, the modeling unit is also used to: establish a three-dimensional model of the pump-turbine and divide the three-dimensional model into different numbers of grids; perform grid independence verification on models with different numbers of grids to determine the optimal number of grids for the numerical calculation model; and divide the three-dimensional model into grids according to the optimal number of grids to obtain the numerical calculation model.

[0018] According to a third aspect, a computer-readable storage medium is provided, wherein the storage medium is used to store a computer program, and the computer program implements the method according to the first aspect when executed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A schematic flow chart of a numerical calculation method for a pump-turbine transient process provided in an embodiment of the present application;

[0020] Figure 2 A schematic structural diagram of a water pump turbine provided in an embodiment of the present application;

[0021] Figure 3 A first schematic diagram of a user-defined program provided in an embodiment of the present application;

[0022] Figure 4 A second schematic diagram of a user-defined program provided in an embodiment of the present application;

[0023] Figure 5 A third schematic diagram of a user-defined program provided in an embodiment of the present application;

[0024] Figure 6 A fourth schematic diagram of a user-defined program provided in an embodiment of the present application;

[0025] Figure 7 A schematic flow chart of a method for establishing a full-flow channel numerical calculation model of a pump-turbine according to an embodiment of the present application;

[0026] Figure 8 is a schematic flow chart of a numerical calculation method provided in another embodiment of the present application;

[0027] Figure 9 It is a schematic structural diagram of a numerical calculation device for the runaway transient process of a pump-turbine provided in an embodiment of the present application. DETAILED DESCRIPTION

[0028] The embodiments of the present application provide a numerical calculation method, device, and storage medium for the transient process of a pump-turbine. The technical solution of the present application is further specifically described below through the embodiments and in conjunction with the accompanying drawings. In the specification, the same or similar figure numbers indicate the same or similar components. The following description of the implementation methods of the present application with reference to the accompanying drawings is intended to explain the overall concept of the present application and should not be understood as a limitation on the present application.

[0029] In the power system, pumped storage power stations are an important energy storage method. Compared with other energy storage methods, they have large energy storage capacity and controllable power generation time, and have high energy storage efficiency. They have been constructed on a large scale in recent years.

[0030] Pumped-storage units are characterized by frequent starts and stops and numerous operating condition changes. Consequently, they frequently experience a variety of complex hydraulic transients, including startup and shutdown, sudden load rejection, runaway, and emergency braking. Furthermore, unexpected power outages during pump-turbine operation are a significant and important phenomenon that cannot be ignored during the pump-turbine transient process. Parameters related to the pump-turbine's external characteristics, such as speed and torque, undergo significant transient changes, making the internal flow field extremely unstable. This is significantly different from the periodic unsteady flow produced during stable operation. This produces a certain degree of transient effects, which are a key factor in causing transient hydraulic shocks or motor overloads. These effects also lead to vibration and noise, significantly impacting the unit's stable operation. Therefore, studying the flow characteristics and mechanical behavior of the fluid within a pump-turbine under transient conditions is of great significance for its optimal design, operational control, and fault diagnosis.

[0031] At present, a feasible way to study the transient process of a pump-turbine is the numerical calculation method. For example, the numerical calculation of the above process is performed through computer simulation software to determine the fluid characteristics and mechanical characteristics in the above transient process.

[0032] However, the simulation-based methods in related technologies still have some shortcomings. More specifically, in some related technologies, numerical calculations usually rely on simplified one-dimensional models, which make it difficult to accurately capture the complex flow characteristics within the flow channel.

[0033] Alternatively, in some related technologies, three-dimensional turbulence numerical simulation can be performed using computational fluid dynamics (CFD) simulation software. This method usually gives fixed inlet and outlet boundary conditions or uses a one-dimensional characteristic line method to obtain the inlet and outlet boundary conditions to numerically simulate the transition process of the turbine model.

[0034] The research objects of the above methods are generally conventional turbines or vane pumps, rather than pumped-storage pump-turbines, and fixed values ​​are used for the inlet and outlet boundary conditions or obtained through the simultaneous one-dimensional characteristic line method. Both methods simplify the boundary conditions to a certain extent, that is, the conditions of the numerical simulation do not match the actual situation, which will affect the accuracy of the external characteristic parameters of the pump-turbine and the internal flow state simulation, resulting in unreliable numerical simulation results.

[0035] Therefore, how to improve the accuracy of numerical calculation of the transient law of characteristic parameters of pump-turbine during the transition process and the dynamic characteristics of the internal flow field has become an urgent problem to be solved.

[0036] In view of the above problems, the present application provides a numerical calculation method, device and storage medium for the transient process of a pump-turbine. The technical solution of the present application will be described in detail below in conjunction with the accompanying drawings.

[0037] Figure 1 is a schematic flow chart of a numerical calculation method for a transient process of a pump-turbine provided in an embodiment of the present application, Figure 1 The method includes steps S110-S130.

[0038] In step S110, a full flow channel numerical calculation model of the pump-turbine is established.

[0039] Figure 2 This is a schematic structural diagram of a pump-turbine provided in an embodiment of the present application. The pump-turbine 200 includes a volute 210, an impeller 220, guide vanes 230 and a tailwater pipe 240.

[0040] The volute is an important foundational component of the pump-turbine, used to evenly introduce water flow with minimal hydraulic losses, allowing the water to smoothly enter subsequent components. The impeller is used for energy conversion. Under turbine conditions, it can convert the kinetic energy and potential energy of the water into rotational mechanical torque. Under pump conditions, it converts the rotational torque into the potential energy of the water. The guide vanes are used to guide the water flow, forming and changing the circulation volume of the rotating water flow entering the volute, ensuring that the turbine has good hydraulic characteristics. The water pipe is used to smoothly guide the water flow at the outlet downstream, allowing the water flow to be discharged smoothly and avoiding turbulence and backflow at the outlet.

[0041] The full-flow channel numerical calculation model established in the solution of the embodiment of the present application is used to simulate the operation process of the water pump and water wheel in the computational fluid dynamics software.

[0042] The embodiments of the present application do not limit the computational fluid dynamics software used for numerical calculations. The computational fluid dynamics software may be, for example, any one of ANSYS Fluent, ANSYS CFX, Flow-3D, etc.

[0043] In the embodiments of the present application, the full-flow channel numerical calculation model of the pump-turbine can be a model that is proportional to the pump-turbine used in actual engineering projects, or, in order to reduce the complexity of numerical calculations and improve calculation efficiency, a proportionally reduced model can be used for calculations based on the principle of similarity.

[0044] It should be noted that when a proportionally reduced model is used in the numerical calculation model, not only geometric similarity should be considered, but also relevant parameters should be determined according to the principles of motion similarity and dynamic similarity to ensure that the motion state of the fluid or object is similar, such as water flow velocity, object rotation speed, etc. Dynamic similarity is the key to ensuring that the mechanical behavior of the model and the prototype is similar. Only when dynamic similarity is met can the mechanical properties of the prototype be accurately predicted.

[0045] Establishing a full-flow numerical model for a pump-turbine involves three-dimensional modeling of the pump-turbine and proper meshing of the 3D model, ultimately yielding the corresponding numerical model. The specific steps of this process will be described in detail later and will not be detailed here.

[0046] Continue reading Figure 1 In step S120, the initial speed and initial torque of the pump-turbine in the initial steady-state condition before the transition process are determined.

[0047] The initial steady-state operating condition before the transition process may refer to the operating state of the pump-turbine at the last moment before the runaway.

[0048] There are many methods for determining the relevant parameters under the initial steady-state condition. As an example, a steady-state calculation method can be used for calculation.

[0049] In step S130 , numerical calculation is performed based on the initial rotational speed and initial torque, the turbulence model used in the numerical calculation, and the inlet and outlet boundary conditions.

[0050] Turbulence models are used to describe fluid characteristics in numerical calculations. They describe the average motion and pulsation characteristics of turbulence, as well as the generation, development, and dissipation of turbulence through a series of mathematical equations and assumptions. Common turbulence models include two-equation models (such as the k-ε model, RNG k-ε model, SST k-ε model, etc.) and the Reynolds-averaged Navier-Stokes equations (RANS) model.

[0051] However, in the embodiment of the present application, the SST k-ω model is selected as the turbulence model. The model adopts the ω equation in the near-wall region, which can more accurately describe the flow characteristics in the boundary layer; because it takes into account the transport process of turbulent shear stress, it can better simulate the shear effect in the flow.

[0052] Furthermore, pump-turbines may experience adverse pressure gradient flow under different operating conditions. For example, under partial load conditions, adverse pressure gradients may appear on the blade surfaces, leading to flow separation and the generation of vortices. The SST k-ω model has excellent predictive capabilities for adverse pressure gradient flows, accurately capturing the flow separation point and the size of the separation region, providing a reliable numerical simulation tool for analyzing pump-turbine performance under complex operating conditions.

[0053] Compared to some complex turbulence models, the SST k-ω model is computationally less complex and more efficient. While ensuring accuracy, it can save computational time and cost, enabling faster results when conducting large-scale numerical simulations of pump-turbine systems, improving research and design efficiency.

[0054] Inlet and outlet boundary conditions are used to specify the values ​​or change patterns of physical quantities such as velocity and pressure at the inlet and outlet of the calculation area in numerical calculations. The selection of this condition should be close to the situation of fluid entering and leaving the calculation area in actual flow, thereby providing a clear boundary constraint for the entire calculation area, so that the numerical calculation can be carried out in a limited area. By simulating the situation of fluid entering and leaving the calculation area in actual flow, the numerical calculation results are closer to the real physical phenomena. If the boundary conditions are set unreasonably, it may cause the calculation results to diverge or non-physical oscillation phenomena to occur. For example, if the pressure is improperly specified at the outlet boundary, it may cause backflow or pressure fluctuations, thereby affecting the stability of the entire calculation. By setting the inlet and outlet boundary conditions reasonably, the numerical calculation can gradually converge to a stable solution during the iteration process, ensuring the reliability of the calculation results.

[0055] In the embodiment of the present application, based on the actual operating conditions of the pump-turbine, the inlet and outlet boundary conditions are set to: the pump-turbine inlet and outlet are open pressure and direction (i.e., set to opening). The reason for this setting is that when the pump-turbine is shut down due to an accident power outage, the flow direction of the fluid in the pump-turbine is determined by the change in dynamic pressure. When the fluid flows into the computational domain boundary, the input relative pressure is considered to be the total pressure; when the fluid flows out of the computational domain boundary, the relative pressure is considered to be the relative static pressure value.

[0056] In the technical solution of the embodiment of the present application, in the process of numerical calculation according to the above conditions, the rotational speed of the impeller of the pump turbine at the second moment is determined based on the rotational speed of the impeller at the first moment, the resultant torque acting on the impeller at the first moment, the rotational relationship of the impeller, and the time step of the numerical calculation; wherein, before the first moment, the time difference between the first moment and the second moment is the above time step, and the resultant torque acting on the impeller at the first moment is determined based on the result of the numerical calculation.

[0057] Unlike related techniques that predefine the impeller's motion pattern before numerical calculation, in this application, the impeller's speed at each moment is related to the numerical result at the previous moment, that is, the impeller speed is iterated cyclically during the numerical calculation. The changes in impeller speed determined based on this method are more consistent with actual operating conditions.

[0058] The following is a detailed description of the method for determining the impeller speed. According to the rotational angular momentum balance equation, the following impeller balance equation is obtained:

[0059]

[0060] In formula (1), M t is the resultant torque acting on the runner; M gis the system load torque; J is the moment of inertia of the pump turbine runner; ω is the angular velocity of the impeller.

[0061] Since the pump-turbine is not loaded after power failure, Mg=0, that is, the rotational angular velocity of the runner at any time is as follows:

[0062]

[0063] In formula (2) is the resultant torque acting on the impeller at the i-th moment, and Δt is the time difference between the first moment and the second moment, that is, the calculation step size.

[0064] The product of the ratio of the resultant torque acting on the impeller at the first moment to the moment of inertia of the impeller and the time step is recorded as the first parameter. The speed of the impeller at the second moment is the sum of the speed at the first moment and the aforementioned first parameter.

[0065] In the embodiment of the present application, the iterative calculation of the impeller speed can be performed by iteratively using a user-defined program, which is described below using the numerical calculation software ANSYS CFX as an example.

[0066] First, create two USER Routine in ANSYS CFX Pre, named TEST and GET_Value respectively (such as Figure 3 shown).

[0067] like Figure 4 As shown, the TEST setting uses the Junction Box Routine option, "Calling Name" is the name of subroutine 1 in the called program folder, "Libraby Name" is the folder name of the called program, "Library Path" is the directory location of the called program file, and "Junction Box Location" is the way to run the program.

[0068] like Figure 5 As shown, the GET_Value setting uses the User CEL Function option, "Calling Name" is the name of subroutine 2 in the called program folder, "Libraby Name" is the folder name of the called program, and "LibraryPath" is the directory location where the called program file is placed.

[0069] The Junction Box Routine is responsible for calculating and updating the rotational speed, and the User CEL Function is responsible for calling the rotational speed in the pre-processing software CFX Pre.

[0070] Then create a USER Function in ANSYS CFX Pre and name it SPEED to call the GET_Value subroutine. The setting of SPEED is as follows: Figure 6 As shown, Figure 6 Where User Routine Name is the name of the USER Routine referenced by the function, Argument Units is the unit of the input variable referenced by the USER Routine, which in this embodiment is s^-1, and Result Units is the unit of the output variable of the USER Routine, which in this embodiment is rad / s. After completing the above settings, you can start the calculation.

[0071] According to the above technical solution, a user-defined program is used to iteratively calculate the rotational speed at the next moment based on the angular momentum equation to achieve continuous updating of the wheel rotational speed at each time step. Each small step is sequentially iterated to obtain the torque, flow rate and other working parameters at the instantaneous moment, thereby increasing the efficiency of the transition process calculation and the accuracy of the calculation results.

[0072] In some embodiments, the aforementioned method further includes: during the numerical calculation process, detecting changes in the resultant torque acting on the impeller, and stopping the numerical calculation when the resultant torque is close to 0.

[0073] The following combination Figure 7 The method for establishing the full flow channel numerical calculation model of the pump-turbine is described in detail.

[0074] like Figure 7 As shown, the above step S110 of establishing the full flow channel numerical calculation model of the pump turbine further includes steps S111-S114.

[0075] In step S111, a three-dimensional model of the pump-turbine is established.

[0076] The three-dimensional digital model of the pump-turbine is the basis for establishing the numerical calculation model. It is necessary to use three-dimensional modeling software (such as SolidWorks, Pro / E, UG, etc.) to build a three-dimensional geometric model of the pump-turbine according to the design drawings or measurement data of the pump-turbine, and ensure that the geometric shape and size of the model are consistent with the actual situation or meet the aforementioned similarity principle.

[0077] In some embodiments, in order to avoid the influence of some structures that have little or no influence on the flow on the computational complexity, appropriate simplification may be performed during the process of establishing the three-dimensional model.

[0078] In step S112, the three-dimensional model is divided into different numbers of grids.

[0079] Meshing is an important step in numerically discretizing the flow control equations in CFD solutions and a key technology for vertical simulation of turbulent flows. The quality of the mesh directly affects the convergence of the analysis and the accuracy of the results.

[0080] This process can be performed using meshing plug-ins or units integrated in fluid numerical calculation software such as ANSYS CFX; alternatively, it can be performed using professional meshing software (ICEM CFD, Gambit, etc.).

[0081] In the process of meshing, models with different numbers of meshes can be generated by adjusting mesh density, mesh type, etc.

[0082] As a possible implementation method, different meshing strategies can also be used, such as structured meshes, unstructured meshes, or hybrid meshes. Structured meshes have higher computational accuracy and better convergence, but are less adaptable to complex geometries. Unstructured meshes can better adapt to complex geometries, but have relatively lower computational accuracy. When meshing, the appropriate mesh type should be selected based on the specific structural characteristics of the pump-turbine, and mesh encryption should be performed in key areas (such as the blade surface and the connection between the volute and the impeller) to improve the ability to capture flow details.

[0083] In step S113, grid independence verification is performed on models with different numbers of grids to determine the optimal number of grids for the numerical calculation model.

[0084] Verifying grid independence involves performing numerical calculations on models with varying mesh sizes and comparing the results (e.g., key performance parameters such as flow rate, velocity, and pressure). When the number of meshes increases to a certain level, and the results no longer change significantly with increasing mesh size, the results are considered grid-independent, and the corresponding mesh size is considered the optimal one.

[0085] As a possible implementation approach, when verifying grid independence, one can use a method of gradually refining the grid, starting with a coarser grid and gradually increasing the number of grids until the calculation results meet the preset accuracy requirements. For example, a relative error threshold can be set, and when the relative error between two consecutive calculation results is less than the threshold, grid independence is considered to have been achieved.

[0086] In step S114, the three-dimensional model is meshed according to the optimal number of meshes to obtain a numerical calculation model.

[0087] After determining the optimal number of grid cells, the 3D model is finally meshed according to this number of grid cells and the previously selected meshing strategy, resulting in a model for numerical calculations. This model accurately simulates the flow field characteristics of the pump-turbine while achieving optimal computational efficiency.

[0088] In some embodiments, the aforementioned method of establishing a numerical calculation model of the entire flow path of a pump-turbine further includes:

[0089] The impeller is set as a rotating dynamic domain, and the volute, the guide vane and the draft tube are set as a static domain;

[0090] During pump-turbine operation, the impeller is a rotating component, and the fluid flow within it has a rotational effect. The volute, guide vanes, and draft tube are stationary components, and the fluid flow within them is relatively stable. By setting the impeller as the rotating dynamic domain and the volute, guide vanes, and draft tube as the stationary domains, different coordinate systems and solution methods can be used to handle the flow in the rotating and stationary regions, respectively, improving the accuracy of the numerical calculations.

[0091] The dynamic-static interface between the rotating domain and the stationary domain is set as the transient rotor stator, and the wall surface of each flow-through component in the pump-turbine is set as the no-slip boundary.

[0092] The transient rotor-stator model takes into account the dynamic interaction between the rotor (impeller) and the stator (volute, guide vanes), and can more accurately simulate the fluid flow and pressure transfer process between the two. By setting the transient rotor-stator interface, the unsteady flow phenomenon caused by the rotation of the impeller can be captured. The no-slip boundary condition means that at the junction of the fluid and the solid wall, the velocity of the fluid is the same as the velocity of the wall, that is, the relative velocity of the fluid on the wall is zero. In the pump-turbine, the wall of each flow-through component is set as a no-slip boundary, which conforms to the actual physical situation and can accurately simulate the fluid flow characteristics near the wall, such as the formation and development of the boundary layer, wall friction, etc.

[0093] The following combination Figure 8 The numerical calculation method provided in the embodiments of the present application is further explained. Figure 8 The method includes steps S801-S806.

[0094] In step S801, a three-dimensional model of the entire flow passage of the pump-turbine flow passage components is established, the calculation domain is divided, and each flow passage component is divided into a structured hexahedral mesh, and mesh independence verification is performed.

[0095] In step S802, a steady-state calculation is performed on the initial steady-state operating condition of the pump-turbine before the power outage and runaway, and steady-state operating parameters of the pump-turbine pump condition are obtained as boundary conditions for transient calculation.

[0096] In step S803, a user-defined program is compiled and called, and the dynamic change process of the wheel speed is controlled by the user-defined program based on the rotational balance equation.

[0097] In step S804, after obtaining the initial torque and initial speed under stable working conditions, a suitable turbulence model is selected and inlet and outlet boundary conditions are set.

[0098] In step S805, secondary development of the ANSYS CFX software is performed, and the rotational speed at the next moment t=t+Δt is iteratively calculated through a user-defined program, so that the wheel rotational speed is continuously updated at each time step. Each small step is sequentially iterated to obtain the torque, flow rate and other working parameters at the instantaneous moment, thereby realizing the calculation of the entire runaway transient process and saving the flow field calculation results at each characteristic moment as needed.

[0099] In step S806, it is determined whether the torque of the impeller is close to 0. If not, step S05 is executed. If yes, it indicates that the result of the numerical calculation has converged.

[0100] Combined with the above Figures 1-8 The method embodiment of the present application is described in detail. The device embodiment of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the description of the device embodiment corresponds to the method embodiment. Therefore, for parts not described in detail, reference can be made to the method embodiment above.

[0101] Figure 9 : is a schematic structural diagram of a numerical calculation device for a pump-turbine runaway transient process provided in an embodiment of the present application, the numerical calculation device comprising:

[0102] The modeling unit 910 is used to establish a numerical calculation model of the entire flow path of the pump-turbine.

[0103] The first determining unit 920 is configured to determine an initial torque and an initial speed of the pump-turbine in an initial steady-state condition before runaway.

[0104] The numerical calculation unit 930 is used to perform numerical calculation based on the initial torque and initial speed, the turbulence model of the numerical calculation, and the inlet and outlet boundary conditions; during the numerical calculation process, the speed of the impeller of the pump turbine at the second moment is determined based on the speed of the impeller at the first moment, the resultant torque acting on the impeller at the first moment, the moment of inertia of the impeller, and the time step of the numerical calculation; wherein, before the first moment, the time difference between the first moment and the second moment is the time step, and the resultant torque acting on the impeller at the first moment is determined based on the result of the numerical calculation.

[0105] In some embodiments, the rotational speed of the impeller at the second moment is the sum of the rotational speed of the impeller at the first moment and a first parameter, and the first parameter is the product of the ratio of the resultant torque acting on the impeller at the first moment to the moment of inertia of the impeller and the time step.

[0106] In some embodiments, the modeling unit is also used to: establish a three-dimensional model of the pump-turbine; divide the three-dimensional model into different numbers of grids; perform grid independence verification on models with different numbers of grids to determine the optimal number of grids for the numerical calculation model; and divide the three-dimensional model into grids based on the optimal number of grids to obtain the numerical calculation model.

[0107] The application embodiments further provide a chip including a processor that can be used to call and execute a computer program from a memory, causing a device equipped with the chip to perform the method described in the above method embodiments. It is understood that the processor can be any of the types of processors mentioned above. It is also understood that the memory can be independent of the chip or integrated into the chip.

[0108] An embodiment of the present application further provides a computer-readable storage medium, wherein the storage medium stores executable code, and when the executable code is executed, the method described in any of the above embodiments is implemented.

[0109] The present application also provides a computer program product. The computer program product includes a program. The computer program product can be applied to the electronic device provided in the present application, and the program enables the computer to execute the method in each embodiment of the present application.

[0110] It should be understood that the units described above as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0111] In various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0112] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0113] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0114] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0115] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from one website, computer, server or data center to another website, computer, server or data center via a wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) method. The computer-readable storage medium can be any available medium that can be read by a computer or a data storage device such as a server or data center that includes one or more available media integrated therein. The available medium may be a magnetic medium (eg, a floppy disk, a hard disk, a magnetic tape), an optical medium (eg, a digital versatile disc (DVD)), or a semiconductor medium (eg, a solid state disk (SSD)).

[0116] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application 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 this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A numerical calculation method for the transient process of a pump-turbine, characterized in that: The method comprises: Establishing a full flow channel numerical calculation model of the pump-turbine; determining an initial torque and an initial speed of the pump-turbine under an initial steady-state operating condition before the transition process; Performing the numerical calculation according to the initial torque and initial speed, the turbulence model of the numerical calculation, and the inlet and outlet boundary conditions; In the numerical calculation process, the rotational speed of the impeller of the pump-turbine at the second moment is determined according to the rotational speed of the impeller at the first moment, the resultant torque acting on the impeller at the first moment, the moment of inertia of the impeller, and the time step of the numerical calculation; The first moment is before the second moment, the time difference between the first moment and the second moment is the time step, and the resultant torque acting on the impeller at the first moment is determined according to the result of the numerical calculation.

2. The method according to claim 1, characterized in that The rotational speed of the impeller at the second moment is the sum of the rotational speed of the impeller at the first moment and a first parameter, and the first parameter is the product of the ratio of the resultant torque acting on the impeller at the first moment to the moment of inertia of the impeller and the time step.

3. The method according to claim 1, characterized in that The method of establishing a numerical calculation model of the entire flow path of a pump-turbine comprises: Establishing a three-dimensional model of the pump-turbine; Performing different numbers of grid divisions on the three-dimensional model; Performing grid independence verification on models with different numbers of grids to determine the optimal number of grids for the numerical calculation model; The three-dimensional model is meshed according to the optimal number of meshes to obtain the numerical calculation model.

4. The method according to claim 3, characterized in that The pump-turbine includes a volute, an impeller, a guide vane, and a tailwater pipe. The method of establishing a numerical calculation model of the entire flow path of the pump-turbine also includes: The impeller is set as a rotating dynamic domain, and the volute, the guide vane and the draft tube are set as a static domain; Setting a transient rotor stator Transient RotorStator at the dynamic and static interface between the rotating dynamic domain and the static domain; The flow-through components in the pump-turbine are avoided to be set as no-slip boundaries.

5. The method according to claim 1, wherein The turbulence model is the SST k-ω model; The inlet and outlet boundary conditions are that the inlet and outlet of the pump turbine are open pressure and direction.

6. The method according to any one of claims 1 to 5, characterized in that The method further comprises: During the numerical calculation, the change of the resultant torque is detected, and the numerical calculation is stopped when the resultant torque approaches 0.

7. A numerical calculation device for the runaway transient process of a pump-turbine, characterized in that: The device comprises: Modeling unit, used to establish the numerical calculation model of the entire flow path of the pump turbine; a first determining unit, configured to determine an initial torque and an initial speed of the pump-turbine under an initial steady-state operating condition before runaway; a numerical calculation unit, configured to perform the numerical calculation according to the initial torque and initial speed, the turbulence model for the numerical calculation, and the inlet and outlet boundary conditions; In the numerical calculation process, the rotational speed of the impeller of the pump-turbine at the second moment is determined according to the rotational speed of the impeller at the first moment, the resultant torque acting on the impeller at the first moment, the moment of inertia of the impeller, and the time step of the numerical calculation; The first moment is before the second moment, the time difference between the first moment and the second moment is the time step, and the resultant torque acting on the impeller at the first moment is determined according to the result of the numerical calculation.

8. The device according to claim 7, characterized in that The rotational speed of the impeller at the second moment is the sum of the rotational speed of the impeller at the first moment and a first parameter, and the first parameter is the product of the ratio of the resultant torque acting on the impeller at the first moment to the moment of inertia of the impeller and the time step.

9. The device according to claim 7, characterized in that The modeling unit is further configured to: Establishing a three-dimensional model of the pump-turbine; Performing different numbers of grid divisions on the three-dimensional model; Performing grid independence verification on models with different numbers of grids to determine the optimal number of grids for the numerical calculation model; The three-dimensional model is meshed according to the optimal number of meshes to obtain the numerical calculation model.

10. A computer-readable storage medium, characterized in that The storage medium is used to store a computer program, and the computer program implements the method according to any one of claims 1 to 6 when executed.

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