Method for evaluating water erosion state of last-stage moving blade of steam turbine

Abstract

The application discloses a kind of steam turbine last stage moving blade water erosion state evaluation method, comprising the following steps: obtaining the flow passage geometric model of steam turbine last stage moving blade and the fluid thermodynamic parameter in last stage moving blade flow passage under operating full condition;Steam turbine last stage moving blade blade geometric model and steam turbine last stage stationary blade blade geometric model are obtained;For the flow passage geometric model and blade geometric model, introduce fluid mechanics control equation, momentum equation, solid mechanics control equation, fluid-solid coupling definition equation;And introduce boundary condition and assumption condition;The flow passage geometric model and blade geometric model are meshed;First, the large eddy simulation method is used to calculate the flow field thermodynamic parameter distribution, then the fluid-solid coupling calculation method is used, the flow field thermodynamic parameter distribution result is transferred to blade for further calculation, and numerical simulation is carried out, to obtain the stress distribution and deformation of last stage moving blade;Water erosion degree is calculated, and the steam turbine last stage moving blade water erosion state is obtained.

Description

Technical Field

[0001] This invention specifically provides a method for evaluating the water erosion state of the last-stage moving blades of a steam turbine based on large eddy simulation and FSI (fluid-solid interaction). Background Technology

[0002] Steam turbines are crucial equipment in thermal and nuclear power plants, and their stability is vital to my country's power security. To reduce power generation and maintenance costs and achieve high turbine stability, there is an urgent need to establish a comprehensive and systematic technology for steam turbine life assessment and prediction. Among these components, the last-stage turbine blades, as a key component, are critical to operational safety.

[0003] Factors affecting blade life are highly nonlinear, including size, material, manufacturing process, and operating conditions. Steam turbine operating conditions are highly variable, and the geometry and flow channels of the last-stage moving blades are complex. Therefore, it is difficult to establish a life prediction model for the last-stage moving blades under water erosion. These factors result in a lack of accuracy and systematicity in the prediction of water erosion of the last-stage moving blades.

[0004] In recent years, computational fluid dynamics and computational solid mechanics have been widely applied in the study of the performance characteristics of steam turbines and related materials. Based on three-dimensional flow theory, the accumulation of advanced experimental data, and the gradual improvement of specialized software, numerical simulation of the last-stage rotor blades can more accurately analyze and predict water erosion characteristics. Compared with pilot-scale tests, numerical simulation tests save economic costs, and because numerical simulation can simulate characteristics under various operating conditions, it provides more comprehensive data for obtaining water erosion characteristics under a wide range of operating conditions. Traditional water erosion prediction techniques for last-stage rotor blades mainly rely on periodic maintenance and steam turbine monitoring systems. These methods can achieve water erosion prediction of last-stage rotor blades to a certain extent, but they have obvious drawbacks, such as the inability to analyze service life in real time, over-reliance on maintenance plans, and limited application scope. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for evaluating the water erosion state of the last stage moving blades of a steam turbine.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for assessing the water erosion state of the last-stage moving blades of a steam turbine includes the following steps:

[0008] Obtain the flow channel geometric model of the last stage moving blade of the steam turbine and the fluid thermodynamic parameters under the design conditions in the flow channel of the last stage moving blade under all operating conditions, including temperature, pressure, velocity, and steam parameters;

[0009] Obtain the blade geometric model of the last stage moving blade and the blade geometric model of the last stage stationary blade of the steam turbine;

[0010] For the aforementioned flow channel geometric model and blade geometric model, fluid dynamics control equations, momentum equations, solid mechanics control equations, and fluid-solid coupling definition equations are introduced; and boundary conditions and assumptions are also introduced.

[0011] The flow channel geometry model and the blade geometry model are meshed;

[0012] First, the large eddy simulation method is used to calculate the distribution of thermal parameters of the flow field (temperature and pressure distribution), especially the temperature and pressure distribution at the interface between the flow field and the moving blade. Then, the fluid-solid coupling calculation equation is used to transfer the results of the flow field thermal parameter distribution to the blade for further calculation and numerical simulation to obtain the stress distribution and deformation of the last stage moving blade.

[0013] A water erosion analysis module is introduced to calculate the degree of water erosion and obtain the water erosion status of the last stage moving blades of the steam turbine.

[0014] According to some preferred embodiments of the present invention, when calculating blade stress using the fluid-solid coupling calculation method, ANSYS software is used to complete the calculation. The ICEM module is used in the meshed blade model, and the material characteristic parameters are imported into ANSYS software. Through the fluid-solid coupling module in ANSYS software, the pressure distribution of the flow field is transferred to the blade structure analysis, and numerical simulation is performed to obtain the stress distribution and deformation of the last-stage moving blade.

[0015] According to some preferred embodiments of the present invention, the evaluation method further includes the following steps: matching and correlating the operating conditions of the steam turbine with the calculated degree of water erosion; monitoring the thermodynamic parameters and operating information of the steam turbine in real time during operation; matching the corresponding degree of water erosion; performing trend analysis; and realizing the prediction of the water erosion state of the last stage moving blades of the steam turbine.

[0016] According to some preferred embodiments of the present invention, the following assumptions are made: the last-stage moving blade is a rigid body, with no relative axial displacement or deformation during operation; the bidirectional coupling effect between the solid boundary forming the flow channel and the fluid is ignored; and the temperature change of the steam in the flow channel is ignored. The purpose of the flow field simulation in this invention is to study the influence of flow field pressure on blade strength; therefore, the influence between temperature change and the flow field pressure distribution is relatively small.

[0017] According to some preferred embodiments of the present invention, during the mesh generation process, for meshes with a quality number less than 0.3, a mesh repair method is used to improve the quality of the mesh, and after mesh repair, a mesh check is performed.

[0018] According to some preferred embodiments of the present invention, the fluid dynamics control equations are as follows:

[0019]

[0020] In the formula, ρ represents fluid density, t represents time, x represents the x-axis direction, y represents the y-axis direction, z represents the z-axis direction, u represents the velocity component of the fluid along the x-axis direction, v represents the velocity component of the fluid along the y-axis direction, and w represents the velocity component of the fluid along the z-axis direction.

[0021] According to some preferred embodiments of the present invention, the momentum equation is as follows:

[0022]

[0023] In the formula, ν represents kinematic viscosity, ρ represents fluid density, F represents fluid body force, and p represents fluid pressure. Let t represent the fluid pressure gradient, t represent time, and V represent the fluid velocity field.

[0024] According to some preferred embodiments of the present invention, the solid mechanics governing equations are as follows:

[0025]

[0026] In the formula, σ xx ,σ xy ,σ xz ,σ yx ,σ yy ,σ yz ,σ zx ,σ zy ,σ zz f represents the stress state at any point in a solid. x ,f y ,f z Represents the volume force of a solid.

[0027] According to some preferred embodiments of the present invention, the fluid-solid coupling definition equation is as follows:

[0028] τ f n f =τ s n s

[0029] In the formula, the subscript f represents fluid, the subscript s represents solid, τ represents stress, and n represents direction.

[0030] According to some preferred embodiments of the present invention, the computational equations for the fluid-solid coupling calculation are as follows:

[0031]

[0032] In the formula, p represents the hydrodynamic pressure in the flow channel, c0 represents the speed of sound in the fluid, T represents the structural load, σ represents the blade stress, f represents the body force, and ρ v ρ represents the blade density, u represents the structural displacement, and ρ represents the blade density. f represents the fluid density, and n represents the direction perpendicular to the boundary.

[0033] According to some preferred embodiments of the present invention, the calculation process of the water erosion degree adopts the nominal stress method, calculates the water erosion effect based on the linear cumulative damage theory, and comprehensively considers the influencing factors such as load conditions, blade average stress and fatigue strength coefficient as the initial setting parameters of the water erosion analysis module to obtain the matching law between the water erosion degree and the working condition.

[0034] Due to the adoption of the above technical solutions, the advantages of the present invention compared with the prior art are as follows: The method for evaluating the water erosion state of the last stage moving blade of the steam turbine of the present invention matches the real-time operating conditions with the water erosion state of the last stage moving blade of the steam turbine, and can calculate the life change of the last stage moving blade caused by water erosion in real time based on the unit operating information, prevent over-reliance on maintenance plans, and effectively avoid insufficient maintenance and over-maintenance. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a schematic diagram of the logic flow of the method for evaluating the water erosion state of the last stage moving blades of a steam turbine in a preferred embodiment of the present invention. Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solutions of the present invention, 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, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0038] The method for predicting the water erosion state of the last-stage moving blades of a steam turbine based on large eddy simulation and FSI in this embodiment specifically includes the following steps:

[0039] Step 1: Obtain the geometric model of the turbine's last-stage moving blade flow channel and the fluid thermodynamic parameters under the design conditions within the last-stage moving blade flow channel under all operating conditions. The thermodynamic parameters under the design conditions are the temperature, pressure, velocity, and steam parameters under various design conditions (rated power condition, maximum continuous power condition, valve fully open power condition, minimum flow condition, turning gear condition, etc.).

[0040] Step 2: Obtain the blade geometry model of the last stage moving blade and the blade geometry model of the last stage stationary blade of the steam turbine.

[0041] Step 3: Introduce the fluid dynamics control equation, momentum equation, solid mechanics control equation, and fluid-solid coupling definition equation.

[0042] The fluid dynamics governing equations, momentum equations, solid mechanics governing equations, and fluid-solid coupling definition equations mentioned above are respectively shown in the following equations:

[0043] 1) Fluid dynamics governing equations:

[0044]

[0045] In the formula, ρ represents fluid density, t represents time, x represents the x-axis direction, y represents the y-axis direction, z represents the z-axis direction, u represents the velocity component of the fluid along the x-axis direction, v represents the velocity component of the fluid along the y-axis direction, and w represents the velocity component of the fluid along the z-axis direction.

[0046] 2) Momentum equation:

[0047]

[0048] In the formula, ν represents kinematic viscosity, ρ represents fluid density, F represents fluid body force, and p represents fluid pressure. Let t represent the fluid pressure gradient, t represent time, and V represent the fluid velocity field.

[0049] 3) Governing equations of solid mechanics:

[0050]

[0051] In the formula, σ xx ,σ xy ,σ xz ,σ yx ,σ yy ,σ yz ,σ zx ,σ zy ,σ zz f represents the stress state at any point in a solid. x ,f y ,f zThe force represents the volume force of a solid, where x represents the x-axis, y represents the y-axis, and z represents the z-axis.

[0052] 4) Definition equation for fluid-solid coupling:

[0053] τ f n f =τ s n s

[0054] In the formula, the subscript f represents fluid, the subscript s represents solid, τ represents stress, and n represents direction.

[0055] Fluid-structure interaction follows the most basic conservation principle. Therefore, at the interface of fluid-structure interaction, that is, the contact surface between the fluid and the moving blade surface, the forces should be balanced.

[0056] Step 4: Introduce boundary conditions and assumptions

[0057] The following assumptions are made: the last-stage moving blade is a rigid body, meaning it has no relative axial displacement or deformation during rotation; the bidirectional coupling effect between the solid boundary forming the flow channel and the fluid is ignored; and the temperature change of the steam in the flow channel is ignored. The purpose of the flow field simulation in this invention is to study the influence of flow field pressure on blade strength; therefore, the influence between temperature change and flow field pressure distribution is relatively small. To simplify the calculation process, a moving blade region and its surrounding flow channel region are taken as the smallest computational unit (sub-region) of the geometric model.

[0058] Boundary conditions: The finite element calculation consists of flow channel thermal calculation and moving blade mechanical calculation.

[0059] The boundary conditions for the flow channel thermal calculation are set as follows: the end face of the stationary vane is set as the inlet, and the front face of the next stage stationary vane is set as the outlet. The inlet pressure, inlet temperature, outlet pressure, and outlet temperature are selected according to the rated power condition, maximum continuous power condition, valve fully open power condition, minimum flow condition, and turning gear condition in step 1. The inlet pressure, inlet temperature, outlet pressure, and outlet temperature also need to be interpolated from the rated power condition, maximum continuous power condition, valve fully open power condition, minimum flow condition, and turning gear condition in step 1 to facilitate the selection of inlet and outlet temperature and pressure for the transition condition.

[0060] The boundary conditions for the mechanical calculation of the moving blade are set as follows: the pressure of steam acting on the surface of the moving blade and the temperature of steam at the junction of the moving blade are set as the boundary conditions of the moving blade surface. Since the fluid-structure interaction of this invention is a one-way interaction, the influence of the deformation of the moving blade on the fluid and heat distribution is ignored.

[0061] Step 5: Mesh the flow channel geometry model and the blade geometry model.

[0062] During the mesh generation process, attention should be paid to the quality of the mesh. For meshes with a quality number of less than 0.3, a mesh repair method should be used to improve the quality of the mesh. After mesh repair, a mesh check should also be performed.

[0063] Step 6: First, use the large eddy simulation method to calculate the temperature and pressure distribution of the flow field, especially the temperature and pressure distribution at the interface between the flow field and the moving blade. Then, use fluid-solid coupling calculation to transfer the calculation results of the flow field to the blade for further calculation. This process does not include the process of transferring the calculation results of the blade to the fluid.

[0064] In the fluid-solid coupling calculation process, Ansys software was used to complete the fluid-solid coupling analysis. After the flow field calculation was completed, the pressure distribution results on the blade surface were extracted for the contact interface between the fluid and the solid structure, i.e., the working and non-working surfaces of the blade model under static structural analysis. Centrifugal force was applied, and under the combined action of multiple loads, contour maps of the blade strength and stress distribution were obtained. The calculation equations and boundary conditions are as follows:

[0065]

[0066] In the formula, p represents the hydrodynamic pressure in the flow channel, c0 represents the speed of sound in the fluid, T represents the structural load, σ represents the blade stress, f represents the body force, and ρ v ρ represents the blade density, u represents the structural displacement, and ρ represents the blade density. f represents the fluid density, and n represents the direction perpendicular to the boundary.

[0067] Specifically, ANSYS software was used to perform fluid-solid coupling calculations. The ICEM module was used to mesh the blade model, and the material characteristic parameters were imported into ANSYS software. Through the fluid-solid coupling module of ANSYS software, the pressure distribution of the flow field (i.e., the distribution of flow field thermodynamic parameters) was transferred to the blade structure analysis and numerical simulation was performed to obtain the stress distribution and deformation of the last stage moving blade.

[0068] Step 7: Use the water erosion analysis module built into ANSYS software to calculate the degree of water erosion.

[0069] The calculation process uses the nominal stress method, calculates the water erosion effect based on the linear cumulative damage theory, and comprehensively considers the influencing factors such as load conditions, blade average stress and fatigue strength coefficient as the initial setting parameters of the water erosion analysis module to obtain the matching law between the degree of water erosion and the working conditions.

[0070] Step 8: Match and correlate the operating conditions and the degree of water erosion. During operation, monitor the operating conditions such as the turbine's thermodynamic parameters in real time. Based on the matching rules obtained in Step 7, match the real-time monitored operating conditions with the water erosion state to achieve water erosion prediction of the turbine's last-stage moving blades based on large eddy simulation and FSI.

[0071] Preferably, steps 1 to 8 can be integrated into a computing cluster, with communication boards and PCs installed. The communication protocols are Modibus and Ethernet. The system can be installed as an external device in the power plant control system and can be connected to the power plant's existing DCS system, thereby enabling the engineering promotion and application of different types of steam turbine units.

[0072] This invention establishes a three-dimensional flow channel and a finite element model of the blade's solid structure in the last-stage turbine. It uses the fluid analysis software ANSYS to calculate the three-dimensional flow field of the last-stage moving blade under different operating conditions. Based on unidirectional fluid-structure interaction (FSI) technology, it performs flow field and strength analysis on the last-stage moving blade. A water erosion analysis module is used to calculate the degree of water erosion in the last-stage moving blade. The water erosion degree of the last-stage moving blade is matched with the full range of operating conditions to predict the degree of water erosion in the last-stage moving blade based on the actual operating conditions of the turbine. The prediction results show that by introducing large eddy simulation (LES) and FSI technology, the strength and water erosion of the last-stage moving blade under all operating conditions can be calculated. The calculation results can better match the operating conditions, thus realizing the prediction of water erosion in the last-stage moving blade of the turbine based on LES and FSI. The prediction results basically meet the prediction accuracy requirements, providing data support for the turbine's operating performance and stability, and reducing safety risks.

[0073] The method for assessing the water erosion state of the last-stage turbine blades of the present invention matches real-time operating conditions with the water erosion state of the last-stage turbine blades. Compared with existing methods, the method of the present invention can calculate the lifespan change of the last-stage turbine blades caused by water erosion in real time based on the unit's operating information, preventing over-reliance on maintenance plans and effectively avoiding insufficient or excessive maintenance. This method can be installed externally in the power plant control system, and its application scope can be extended to various types of turbine units.

[0074] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for assessing the water erosion state of the last-stage moving blades of a steam turbine, characterized in that, Includes the following steps: Obtain the flow channel geometric model of the last stage moving blade of the steam turbine and the fluid thermodynamic parameters in the flow channel of the last stage moving blade under all operating conditions; Obtain the blade geometric model of the last stage moving blade and the blade geometric model of the last stage stationary blade of the steam turbine; For the aforementioned flow channel geometric model and blade geometric model, fluid dynamics control equations, momentum equations, solid mechanics control equations, and fluid-solid coupling definition equations are introduced; Boundary conditions and assumptions are introduced; The flow channel geometry model and the blade geometry model are meshed; First, the large eddy simulation method is used to calculate the distribution of flow field thermodynamic parameters. Then, the fluid-solid coupling calculation method is used to transfer the results of the flow field thermodynamic parameter distribution to the blade for further calculation and numerical simulation to obtain the stress distribution and deformation of the last stage moving blade. A water erosion analysis module is introduced to calculate the degree of water erosion and obtain the water erosion status of the last stage moving blades of the steam turbine; The evaluation method also includes the following steps: matching and correlating the operating conditions of the steam turbine with the calculated degree of water erosion, monitoring the thermodynamic parameters of the steam turbine in real time during operation, and matching the corresponding degree of water erosion to achieve prediction of the water erosion state of the last stage moving blades of the steam turbine. The assumptions are as follows: the last stage blade is a rigid body, and there is no relative axial displacement or deformation during rotation; the bidirectional coupling effect between the solid boundary forming the flow channel and the fluid is ignored; and the temperature change of the steam in the flow channel is ignored. The boundary conditions include the boundary conditions for flow channel thermodynamic calculation: the end face of the stationary blade is set as the inlet, the front end face of the next stage stationary blade is set as the outlet, and the inlet pressure, inlet temperature, outlet pressure, and outlet temperature are selected and interpolated according to the fluid thermodynamic parameters in the final stage moving blade flow channel under all operating conditions. The boundary conditions include the boundary conditions for the mechanical calculation of the moving blade: the pressure of steam acting on the surface of the moving blade and the temperature of steam at the junction of the moving blade are set as the boundary conditions of the moving blade surface, and the influence of moving blade deformation on fluid and heat distribution is ignored. The calculation process of the water erosion degree adopts the nominal stress method, calculates the water erosion effect based on the linear cumulative damage theory, and comprehensively considers the load conditions, the average stress of the blade and the fatigue strength coefficient. In the fluid-solid coupling calculation process, Ansys software is used to complete the fluid-solid coupling analysis. After the flow field calculation is completed, the pressure distribution results on the blade surface are extracted for the contact interface between the fluid and the solid structure, that is, the working surface and non-working surface of the blade model under static structural analysis. Centrifugal force is applied, and under the combined action of multiple loads, the cloud map of blade strength and stress distribution is obtained.

2. The evaluation method according to claim 1, characterized in that, During the mesh generation process, for meshes with a quality number less than 0.3, a mesh repair method is used to improve the quality of the mesh, and a mesh check is performed after mesh repair.

3. The evaluation method according to claim 1, characterized in that, The fluid dynamics control equations are shown below: ； In the formula, Indicates fluid density, Indicates time, Indicates along x Axial direction, Indicates along y Axial direction, Indicates along z Axial direction, Indicates fluid along x axial velocity components Indicates fluid along y axial velocity components Indicates fluid along z The velocity component in the axial direction.

4. The evaluation method according to claim 1, characterized in that, The momentum equation is shown below: ； In the formula, Indicates kinematic viscosity. Indicates fluid density, Represents fluid mass force. Indicates fluid pressure. Represents the fluid pressure gradient. Indicates time, Represents the fluid velocity field.

5. The evaluation method according to claim 1, characterized in that, The governing equations for solid mechanics are shown below: ； In the formula, This represents the stress state at any point in a solid. Represents the volume force of a solid.

6. The evaluation method according to claim 1, characterized in that, The fluid-solid coupling definition equation is shown below: ； In the formula, the subscript f represents a fluid, and the subscript s represents a solid. Indicates stress, Indicates direction.

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