Method for analyzing erosion characteristics of steam turbine governing valve based on modified oka erosion model

Abstract

The application discloses a method for analyzing the erosion characteristics of a steam turbine regulating valve based on a modified Oka erosion model, which comprises the following steps: S1, modifying the parameters of the Oka erosion model; S2, analyzing the flow field characteristics; and S3, analyzing the erosion characteristics. By constructing a single particle impact three-dimensional model and performing explicit dynamic finite element simulation, the particle size, impact velocity and impact angle parameters in the Oka erosion model are modified, so that the erosion prediction model is matched with the actual valve core material and high temperature and high pressure working conditions, and the accuracy of the erosion rate calculation is improved. By establishing a three-dimensional entity model of the regulating valve and extracting a fluid domain for flow field numerical simulation, the distribution of the velocity field and the pressure field in the valve is obtained, the modified Oka erosion model is introduced and coupled with the solid particle parameters, the particle motion equation and the particle-wall collision model are solved, and the distribution of the erosion and wear of the valve core surface is obtained, so that the positioning accuracy of the erosion area under the complex gas-solid two-phase flow is improved.

Description

Technical Field

[0001] This invention relates to a method for analyzing the erosion characteristics of turbine control valves based on a modified Oka erosion model, and belongs to the technical field of turbine equipment. Background Technology

[0002] Steam turbines, as key components in coal-fired power units, nuclear power units, gas-fired combined cycle power units, and solar thermal power units, hold an extremely important position in modern power and industrial sectors. They convert the heat energy generated from fuel into mechanical energy to drive generators, providing a stable and reliable power supply. This not only supports the operation of industrial production lines but also provides essential electricity for homes and public utilities. Furthermore, steam turbines are widely used in ship propulsion, oil refining, and chemical production, playing a crucial role. A large portion of the world's electricity is generated by steam turbines as prime movers, and the development and innovation of steam turbine technology have made a significant contribution to the national economy.

[0003] For high-performance steam turbine units, the main steam regulating valve is a critical component controlling the turbine, often referred to as the "throat" of the industrial system. It not only controls the amount of steam entering the turbine during normal operation by adjusting the valve opening to meet the unit's load requirements, but also quickly closes in case of malfunction or emergency, cutting off the steam passage and preventing overspeeding and subsequent damage. Therefore, the performance and reliability of the main steam regulating valve directly affect the reliability of the steam turbine unit. It is worth noting that the internal flow of the regulating valve in actual operation is far from an ideal single-phase compressible flow; rather, it is a complex gas-solid two-phase flow carrying oxide shedding from pipelines or tiny solid particles from the boiler. These solid particles are mainly formed from the shedding of scale layers from the boiler superheater and main steam pipelines; these particles are relatively hard and mostly in a flat, plate-like form.

[0004] During the long-term operation of steam turbines, leakage problems in the control valves frequently occur, leading to reduced unit speed regulation performance and even, in some cases, significant internal steam leakage into the unit when the valves are closed, preventing normal shutdown. Analysis reveals that erosion and wear on the valve core surface caused by long-term impact from high-temperature, high-pressure steam and solid particles are the main reasons affecting valve sealing, regulation accuracy, and service life. Control valves operate under extremely harsh conditions, particularly under low-load conditions with significant pressure differentials, making them highly susceptible to erosion of valve components.

[0005] Currently, there are significant limitations in the prediction methods and mechanism analysis for erosion wear of turbine control valves. On the one hand, the working medium of the control valve is a high-temperature, high-pressure, viscous compressible turbulent flow with complex internal channel shapes and drastic changes in flow characteristics. However, traditional erosion prediction methods fail to fully incorporate the coupling effect of steam compressibility, particle shape coefficient, and concentration under high-temperature and high-pressure conditions, leading to significant deviations between simulation results and actual service conditions. On the other hand, in the field of erosion wear numerical simulation, the Oka model is widely considered one of the erosion models with relatively high prediction accuracy. However, the empirical constants and parameter system of the Oka model are mainly based on experimental data from conventional materials such as carbon steel, stainless steel, and aluminum alloys. In contrast, the valve core of a turbine control valve experiences high impact velocities and complex particle size distributions under actual service conditions, and the valve core material is often surface-hardened. Its erosion behavior differs significantly from the material reference used in the model's development. Studies have shown that the difference between the pipe material type on which the Oka model is based and the actual material leads to significant deviations in the predicted erosion amount. When the Oka model is directly applied to predict erosion of turbine control valves that do not match actual material parameters, the prediction error is large and it cannot accurately guide valve body structure optimization and erosion resistance improvement. Summary of the Invention

[0006] Purpose of the invention: To address the shortcomings of existing technologies, this invention provides a method for analyzing the erosion characteristics of turbine control valves based on a modified Oka erosion model. This invention achieves accurate prediction of the erosion characteristics of turbine control valves by modifying the Oka erosion model, combining flow field analysis and particle-flow field coupling calculations, and quantifying the influence of multiple factors.

[0007] Technical solution: A method for analyzing the erosion characteristics of turbine control valves based on the modified Oka erosion model, including the following steps:

[0008] S1: Oka erosion model parameter correction:

[0009] S1-1: Establish the explicit basic dynamic equations and construct a three-dimensional model of single-particle impact including particles and valve core;

[0010] S1-2: Set the material properties of the particles and valve core, mesh the single-particle impact three-dimensional model, and set boundary conditions and loads in combination with working parameters to obtain a calculable finite element model;

[0011] S1-3: Based on the finite element model, perform explicit dynamic finite element simulation analysis to calculate the volume of the pits on the valve core surface under different working conditions;

[0012] S1-4: Using the pit volume under the benchmark working condition as a benchmark, analyze the correlation between particle size, impact velocity and impact angle and erosion rate. Based on this, correct the parameters of the Oka erosion model to obtain the corrected Oka erosion model and send it to step S3.

[0013] S2: Flow field characteristic analysis:

[0014] S2-1: Establish a fluid dynamics mechanism model and extract the geometric structural features of the turbine control valve cavity to construct a three-dimensional solid model including the valve body, valve core, valve stem, valve cage, and valve cover.

[0015] S2-2: Based on the three-dimensional solid model, the flow channel of the valve cavity is extracted to obtain the fluid domain geometric model of the regulating valve;

[0016] S2-3: Mesh the fluid domain geometric model, set the material properties and flow boundary conditions of the steam, and thus establish a solvable numerical model of the flow field;

[0017] S2-4: Based on the numerical model of the flow field, perform finite volume method simulation analysis, simulate and calculate the velocity field and pressure field distribution in the flow field, obtain the velocity field and pressure field distribution data in the flow field, and send the flow field analysis results to step S3;

[0018] S3: Erosion Characteristics Analysis:

[0019] S3-1: Receive the modified Oka erosion model output from step S1 and the flow field analysis results output from step S2, and introduce the erosion wear theory and the modified Oka erosion model based on the flow field analysis results.

[0020] S3-2: Set solid particle parameters and perform coupled calculations with the flow field to solve the particle motion equation and particle-wall collision model, thereby obtaining the erosion distribution generated during the operation of the control valve.

[0021] S3-3: Based on the erosion distribution, the erosion wear distribution results on the valve core surface are obtained.

[0022] In the preferred embodiment, the establishment of the explicit fundamental dynamic equations in S1-1 specifically involves:

[0023] mass conservation equation:

[0024]

[0025] In the formula, ρ0 is the initial density of the current volume of the region; V0 is the initial volume of the current volume of the region; m is the current mass corresponding to the current volume of the region; and V is the current volume of the region.

[0026] Momentum conservation equation:

[0027]

[0028] In the formula, ρ is the density; , , Acceleration in the x, y, and z directions, respectively; Let be the stress tensor.

[0029] Energy conservation equation:

[0030]

[0031] In the formula, For strain tensor; It is energy.

[0032] The original formula for the Oka erosion model is:

[0033]

[0034]

[0035]

[0036] In the formula, E(θ) represents the erosion rate; f(θ) represents the impact angle function; E 90 The value represents the reference erosion rate at an impact angle of 90°; K is a particle property constant, K1 is the hardness index factor, K2 is the velocity index factor, and K3 is the particle size index factor, where... In the simulation, they are combined into a single wear constant; v, v', D, and D' represent the velocity, reference velocity, particle size, and reference particle diameter in the experiment, respectively; Hv is the Vickers hardness of the material.

[0037] Preferably, the material properties in S1-2 include the density, Young's modulus, Poisson's ratio, and specific heat at constant pressure of the particles, as well as the density, Young's modulus, Poisson's ratio, coefficient of linear expansion, yield stress, and tangential modulus of the valve core.

[0038] The operating parameters include particle size, impact velocity, and impact angle.

[0039] The number of meshes was determined by mesh independence verification, and the convergence criterion was that the maximum deformation change of the valve core target material was less than 0.1%.

[0040] In a preferred embodiment, the boundary conditions and loads set in S1-2 are specifically as follows: the lower surface of the valve core is used as a fixed constraint; the friction between the solid particles and the valve core is described by a penalty function, and the Coulomb friction coefficient is 0.25.

[0041] The penalty function is expressed as:

[0042]

[0043] In the formula, F n For contact force; k n For contact stiffness; x p This refers to the penetration amount.

[0044] Preferably, the calculation of the pit volume on the valve core surface under different operating conditions in S1-3 is specifically as follows:

[0045] When a particle impacts the valve core at a 90° angle, the morphology of its pit is relatively regular, and it can be calculated by the pit radius and depth; when a particle impacts the valve core at other angles, the pit often has an irregular shape, so it can be characterized by plastic work.

[0046] Calculation of pit volume:

[0047]

[0048] In the formula, V is the volume of the pit; d is the diameter of the pit; and h is the depth of the pit.

[0049] Preferably, the parameter correction in S1-4 specifically includes:

[0050] Particle size parameter correction:

[0051]

[0052] In the formula, V D D is the pit volume; D is the particle size; D' is the reference particle size.

[0053] Impact velocity parameter correction:

[0054]

[0055] In the formula, V v v is the pit volume; v is the particle impact velocity; v' is the particle reference impact velocity.

[0056] Impact angle parameter correction:

[0057]

[0058] In the formula, V θ θ is the pit volume; θ is the particle impact angle; Hv is the Vickers hardness of the material.

[0059] The modified Oka erosion model expression is as follows:

[0060] The erosion rate of the valve core surface is related to the particle size, impact velocity, impact angle, and its own material properties. Combining equation (9-11), the wear rate of a unit mass of particles impacting the valve core surface is:

[0061]

[0062] In the formula, E is the erosion rate per unit mass of solid particles; ρ0 is the density of the valve core material; ρ is the particle density. Substituting into formula (9-11), the combined erosion rate is:

[0063]

[0064] Preferably, the mechanism model for establishing fluid dynamics in S2-1 is specifically as follows:

[0065] mass conservation equation:

[0066]

[0067] In the formula, ρ represents density; t represents time; This represents the velocity vector.

[0068] Momentum conservation equation:

[0069]

[0070] In the formula, u, v, and w represent the velocity components in the x, y, and z directions, respectively; τ xx , τ xy , τ xz F represents the component of the viscous stress on the surface of the infinitesimal element; p represents the pressure on the infinitesimal element; x F y F z This represents the force acting on a infinitesimal element.

[0071] Energy conservation equation:

[0072]

[0073] In the formula, T represents temperature; k represents the fluid heat transfer coefficient; c P S represents specific heat capacity. T This represents the viscous dissipation term.

[0074] Turbulence model:

[0075]

[0076]

[0077]

[0078] In the formula, ; ; ; ; ; ; ; .

[0079] In a preferred embodiment, the material properties of the steam in S2-3 include density, specific heat capacity, thermal conductivity, viscosity, and molecular weight.

[0080] Flow boundary conditions include inlet pressure, inlet temperature, turbulence model parameters, and wall conditions;

[0081] The mesh generation method uses a polyhedral core volume mesh to refine the throttling window and valve core region. The mesh number is determined by verifying mesh independence and using the outlet flow rate change of less than 0.1% as the convergence criterion.

[0082] Preferably, in step S3-2, the solid particle parameters include particle size, particle shape factor, and particle concentration; the particle motion equation is:

[0083]

[0084] In the formula, m p Indicates particle mass; Indicates particle velocity; ρ represents fluid velocity. p ρ represents particle density; ρ represents fluid density. It represents the sum of additional forces such as Saffman lift, Magnus lift, and pressure gradient force. The relaxation time of a particle is expressed as follows:

[0085]

[0086] Traction coefficient C D Represented as:

[0087]

[0088] In the formula, b1 = exp(2.3288 - 6.4581φ + 2.4486φ). 2 ); b2=0.0964+0.5565φ; b3=exp(4.905-13.8944φ+18.4222φ 2 -10.2599φ 3 ); b4=exp(1.4681+12.2584φ-20.7322φ 2 +15.8855φ 3 The expression for the relative Reynolds number Re is as follows:

[0089]

[0090] In the formula, d p μ represents the particle diameter; μ represents the viscosity of the continuous phase molecules; φ represents the particle shape factor.

[0091] The particle-wall collision model is as follows:

[0092]

[0093] In the formula, u p1 and v p1 Represents the normal and tangential velocity components before particle collision; u p2 and v p2 This represents the normal and tangential velocity components after a particle collision.

[0094] In the preferred embodiment, S3-3 specifically refers to:

[0095] Grey relational analysis was used to quantify the influence of valve opening, particle size, particle shape factor, and particle concentration on the erosion wear of the control valve core.

[0096] Determine the reference sequence and comparison sequence: Using the maximum erosion rate of the control valve core surface as the reference sequence Y, and factors such as valve opening degree as the comparison sequence X, they are respectively expressed as:

[0097]

[0098]

[0099] In the formula: n is the number of sample points.

[0100] Normalization of variables: To eliminate the influence of differences in units and orders of magnitude among factors, the data is normalized using the mean method.

[0101]

[0102]

[0103] Calculate the grey relational coefficient: First, calculate the absolute value of the difference between each factor sequence after normalization and the reference sequence; then calculate the grey relational coefficient between the comparison sequence and the reference sequence.

[0104]

[0105]

[0106] Calculating the grey relational degree: For each reference sequence, the average of its relational coefficients is the relational degree.

[0107]

[0108] In the formula, i = 1, 2, 3, 4; , ρ represents the minimum and maximum absolute values ​​of all differences; ρ is the resolution coefficient, which is 0.5.

[0109] Beneficial effects: This invention constructs a three-dimensional model of single-particle impact and performs explicit dynamic finite element simulation, correcting the particle size, impact velocity, and impact angle parameters in the Oka erosion model. This makes the erosion prediction model match the actual valve core material and high-temperature, high-pressure conditions, improving the accuracy of erosion rate calculation. Simultaneously, by establishing a three-dimensional solid model of the regulating valve and extracting the fluid domain for flow field numerical simulation, the velocity and pressure field distributions within the valve are obtained. Based on this, the corrected Oka erosion model is introduced and coupled with solid particle parameters to solve the particle motion equation and particle-wall collision model, thereby obtaining the distribution of erosion wear on the valve core surface and improving the positioning accuracy of the erosion region under complex gas-solid two-phase flow. Furthermore, the grey relational analysis method is used to quantify the influence of valve opening, particle size, particle shape coefficient, and particle concentration on valve core erosion wear, effectively revealing the erosion control mechanism under multi-factor coupling. This can meet the requirements of high-performance turbine regulating valve anti-erosion optimization design and service life assessment. Attached Figure Description

[0110] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0111] Figure 1 This is a flowchart of the method of the present invention;

[0112] Figure 2 For single-particle impact model and mesh generation;

[0113] Figure 3 A three-dimensional model of the control valve;

[0114] Figure 4 The pressure and velocity field distributions under different opening degrees are shown.

[0115] Figure 5 The curve showing the relationship between the maximum erosion rate of the valve core surface and the number of particles;

[0116] Figure 6 The erosion wear distribution on the valve core surface under different opening degrees;

[0117] Figure 7 The erosion wear distribution on the valve core surface under different particle sizes;

[0118] Figure 8 The erosion wear distribution on the valve core surface under different particle shape coefficients;

[0119] Figure 9 The erosion wear distribution on the valve core surface under different particle concentrations;

[0120] Figure 10 The grey relational degree corresponds to different factors. Detailed Implementation

[0121] 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 are within the scope of protection of the present invention.

[0122] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0123] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0124] like Figure 1 As shown, the method for analyzing the erosion characteristics of turbine control valves based on the modified Oka erosion model includes the following steps:

[0125] S1: Oka erosion model parameter correction:

[0126] S1-1: Establish the explicit basic dynamic equations and construct a three-dimensional model of single-particle impact including particles and valve core;

[0127] The specific steps to establish the explicit fundamental equations of dynamics are as follows:

[0128] mass conservation equation:

[0129]

[0130] In the formula, ρ0 is the initial density of the current volume of the region; V0 is the initial volume of the current volume of the region; m is the current mass corresponding to the current volume of the region; and V is the current volume of the region.

[0131] Momentum conservation equation:

[0132]

[0133] In the formula, ρ is the density; , , Acceleration in the x, y, and z directions, respectively; Let be the stress tensor.

[0134] Energy conservation equation:

[0135]

[0136] In the formula, For strain tensor; For energy;

[0137] The original formula for the Oka erosion model is:

[0138]

[0139]

[0140]

[0141] In the formula, E(θ) represents the erosion rate; f(θ) represents the impact angle function; E 90 This represents the reference erosion rate at an impact angle of 90°; K is a particle property constant, K1 is the hardness index factor, K2 is the velocity index factor, and K3 is the particle size index factor, where... In the simulation, they are combined into a single wear constant; v, v', D, and D' represent the velocity, reference velocity, particle size, and reference particle diameter in the experiment, respectively; Hv is the Vickers hardness of the material.

[0142] S1-2: Set the material properties of the particles and valve core, mesh the single-particle impact three-dimensional model, and set boundary conditions and loads in combination with working parameters to obtain a calculable finite element model;

[0143] Material properties include particle density, Young's modulus, Poisson's ratio, and specific heat at constant pressure, as well as valve core density, Young's modulus, Poisson's ratio, coefficient of linear expansion, yield stress, and tangent modulus.

[0144] The operating parameters include particle size, impact velocity, and impact angle.

[0145] The number of meshes was determined by mesh independence verification, and the convergence criterion was that the maximum deformation change of the valve core target material was less than 0.1%.

[0146] The boundary conditions and loads are set as follows: the lower surface of the valve core is used as a fixed constraint; the friction between the solid particles and the valve core is described by a penalty function, and the Coulomb friction coefficient is 0.25.

[0147] The penalty function is expressed as:

[0148]

[0149] In the formula, F n For contact force; k n For contact stiffness; x p This refers to the penetration amount.

[0150] Through the analysis of the erosion mechanism, particles play a key role in erosion wear. In order to accurately predict the erosion wear of the control valve core, this paper focuses on particle properties and conducts simulation analysis on different particle sizes, impact velocities and impact angles based on the ANSYS explicit dynamics module.

[0151] Single-particle impact model, such as Figure 2 As shown, the particulate material is Fe2O3, the valve core material is 25Cr2MoVA, and the temperature is set to 213℃. The baseline operating conditions and specific parameters of the particulates are shown in Tables 1 and 2.

[0152] Table 1: Baseline Operating Conditions

[0153]

[0154] Table 2: Particle Parameters

[0155]

[0156] In this paper, the valve core is simulated and analyzed using 25Cr2MoVA. 25Cr2MoVA is a special high-performance alloy steel for high temperature and high pressure environments. Under complex environments of high temperature, high pressure, long-term stress and corrosive steam media, it can maintain its structural integrity, dimensional stability and sealing function for a long time and reliably.

[0157] Particle parameters were incorporated into a single-particle erosion model for finite element analysis.

[0158] In simulation, mesh accuracy plays a crucial role in the accuracy of the simulation results. The Mesh module was used to mesh the single-particle impact model. Spherical particles were meshed using tetrahedral meshes, while valve core targets were meshed using hexahedral meshes. To ensure computational accuracy and efficiency, the maximum deformation of the valve core target was selected as the evaluation criterion. Mesh independence was verified for the above models, as shown in Table 3. When the mesh count increased from 468242 to 650642, the average mesh quality was higher, and the maximum deformation change of the valve core was less than 0.1%. To save computational resources, this paper selected the finite element model with a mesh count of 468242 for subsequent calculations, as shown in Table 3. Figure 2 As shown.

[0159] Table 3: Mesh Independence Analysis

[0160]

[0161] S1-3: Based on the finite element model, perform explicit dynamic finite element simulation analysis to calculate the volume of the pits on the valve core surface under different working conditions, as shown in Tables 4, 5 and 6.

[0162] The specific calculation of the pit volume on the valve core surface under different operating conditions is as follows:

[0163] When a particle impacts the valve core at a 90° angle, the morphology of its pit is relatively regular, and it can be calculated by the pit radius and depth; when a particle impacts the valve core at other angles, the pit often has an irregular shape, so it can be characterized by plastic work.

[0164] Calculation of pit volume:

[0165]

[0166] In the formula, V is the volume of the pit; d is the diameter of the pit; and h is the depth of the pit.

[0167] Table 4: Pits on the surface of the valve core under different particle sizes

[0168]

[0169] Table 5: Dent volume on valve core surface at different impact velocities

[0170]

[0171] Table 6: Dimples on the valve core surface at different impact angles

[0172]

[0173] S1-4: Using the pit volume under the benchmark working condition as a benchmark, analyze the correlation between particle size, impact velocity and impact angle and erosion rate. Based on this, correct the parameters of the Oka erosion model to obtain the corrected Oka erosion model and send it to step S3.

[0174] Parameter correction specifically includes:

[0175] Particle size parameter correction:

[0176]

[0177] In the formula, V D D is the pit volume; D is the particle size; D' is the reference particle size.

[0178] Impact velocity parameter correction:

[0179]

[0180] In the formula, V v v is the pit volume; v is the particle impact velocity; v' is the particle reference impact velocity.

[0181] Impact angle parameter correction:

[0182]

[0183] In the formula, V θ θ is the pit volume; θ is the particle impact angle; Hv is the Vickers hardness of the material, Hv=2.7146GPa.

[0184] The modified Oka erosion model expression is as follows:

[0185] The erosion rate of the valve core surface is related to the particle size, impact velocity, impact angle, and its own material properties. Combining equation (9-11), the wear rate of a unit mass of particles impacting the valve core surface is:

[0186]

[0187] In the formula, E is the erosion rate per unit mass of solid particles; ρ0 is the density of the valve core material; ρ is the particle density. Substituting into formula (9-11), the combined erosion rate is:

[0188]

[0189] S2: Flow field characteristic analysis:

[0190] S2-1: Establish a fluid dynamics mechanism model and extract the geometric structural features of the turbine control valve cavity to construct a three-dimensional solid model including the valve body, valve core, valve stem, valve cage, and valve cover.

[0191] The specific steps for establishing the mechanistic model of fluid mechanics are as follows:

[0192] mass conservation equation:

[0193]

[0194] In the formula, ρ represents density; t represents time; This represents the velocity vector.

[0195] Momentum conservation equation:

[0196]

[0197] In the formula, u, v, and w represent the velocity components in the x, y, and z directions, respectively; τxx , τ xy , τ xz F represents the component of the viscous stress on the surface of the infinitesimal element; p represents the pressure on the infinitesimal element; x F y F z This represents the force acting on a infinitesimal element.

[0198] Energy conservation equation:

[0199]

[0200] In the formula, T represents temperature; k represents the fluid heat transfer coefficient; c P S represents specific heat capacity. T This represents the viscous dissipation term.

[0201] Turbulence model:

[0202]

[0203]

[0204]

[0205] In the formula, ; ; ; ; ; ; ; .

[0206] S2-2: Based on the aforementioned three-dimensional solid model, the flow channel of the valve cavity is extracted to obtain the fluid domain geometric model of the control valve; the control valve, as the research object, mainly consists of a valve body, valve core, valve stem, valve cage, and valve cover, wherein the valve cage has throttling windows on all four sides, such as... Figure 3 As shown, DesignModeler was used to extract the flow path from the valve's internal cavity.

[0207] S2-3: Mesh the fluid domain geometric model, set the material properties and flow boundary conditions of the steam, and thus establish a solvable numerical model of the flow field;

[0208] The material properties of steam include density, specific heat capacity, thermal conductivity, viscosity, and molecular weight;

[0209] Flow boundary conditions include inlet pressure, inlet temperature, turbulence model parameters, and wall conditions;

[0210] The mesh generation method uses a polyhedral core volume mesh to refine the throttling window and valve core region. The mesh number is determined by verifying mesh independence and using the outlet flow rate change of less than 0.1% as the convergence criterion.

[0211] The fluid domain was partitioned using ANSYS Fluent Meshing software and the polyhedral core volume mesh generation method. Mesh refinement was applied to key areas affecting flow characteristics, such as bends, valve throttling windows, and the valve core region. Boundary layer meshing was performed near the wall, with the first layer mesh height set to 0.02 mm. To ensure the calculation results were unaffected by mesh density, mesh independence was verified for the flow field of a control valve with a 30% opening. Six mesh schemes were designed as shown in Table 7. Comparison of the outlet flow rates under each scheme revealed that the outlet flow rate remained essentially unchanged when the mesh count reached 2,837,630. Considering both computational accuracy and efficiency, a mesh with 2,837,630 elements was selected for subsequent calculations.

[0212] Table 7: Mesh independence analysis:

[0213]

[0214] The fluid medium in this paper is compressible superheated steam, and an ideal gas model is used. Its density is related to the working pressure and temperature of the steam. The inlet pressure is set to 2 MPa and the temperature to 213 °C. The solver uses a pressure-based steady-state solution, and the turbulence model is a Realizable k-ε model with a turbulence intensity of 5% and a hydraulic diameter of 0.05 m. A semi-implicit method using a consistent pressure coupling equation set is employed. The spatiotemporal discretization equations for turbulent kinetic energy k and turbulent dissipation rate ε, as well as the momentum and energy equations, are presented in a second-order upwind scheme. The fluid-wall contact boundary is set as an adiabatic no-slip wall.

[0215] S2-4: Based on the numerical model of the flow field, perform finite volume method simulation analysis, simulate and calculate the velocity field and pressure field distribution in the flow field, obtain the velocity field and pressure field distribution data in the flow field, and send the flow field analysis results to step S3;

[0216] The pressure and velocity field distributions of the control valve at different opening degrees are as follows: Figure 4 As shown, from Figure 4As can be seen, the pressure distribution of steam before entering the throttling window is uniform, and the pressure value remains basically constant, approximately equal to the inlet pressure. After entering the throttling window, the steam pressure decreases rapidly within a short stroke, creating a certain pressure gradient. After passing through the throttling window and entering the outlet channel, the steam pressure increases slightly, eventually stabilizing at the outlet pressure. Furthermore, as the valve opening increases, the pressure gradient at the throttling window and the pressure difference within the valve decrease significantly. The steam velocity is relatively stable at the inlet. As the steam passes through the throttling window, the steam velocity continuously increases, reaching its maximum at the outlet of the throttling window. After entering the outlet pipe of the valve, the steam velocity gradually decreases. With increasing valve opening, the maximum steam velocity inside the valve gradually decreases.

[0217] S3: Erosion Characteristics Analysis:

[0218] S3-1: Receive the modified Oka erosion model output from step S1 and the flow field analysis results output from step S2, and introduce the erosion wear theory and the modified Oka erosion model based on the flow field analysis results.

[0219] S3-2: Set solid particle parameters and perform coupled calculations with the flow field to solve the particle motion equation and particle-wall collision model, thereby obtaining the erosion distribution generated during the operation of the control valve.

[0220] Solid particle parameters include particle size, particle shape factor, and particle concentration; the particle motion equation is:

[0221]

[0222] In the formula, m p Indicates particle mass; Indicates particle velocity; ρ represents fluid velocity. p ρ represents particle density; ρ represents fluid density. This represents the sum of additional forces, including Suffman lift, Magnus lift, and pressure gradient force. Suffman lift is generated by the shear stress of the fluid acting on the particles. Magnus lift is generated by the interaction between the fluid and the solid, resulting in a pressure difference at the solid surface. The effects of Suffman and Magnus lift on the flow field are small and can be ignored. Pressure gradient force is the additional pressure generated by the pressure gradient acting on the particles. In steam turbine control valves, steam expansion causes a significant pressure drop; therefore, pressure gradient force cannot be ignored. The relaxation time of a particle is expressed as follows:

[0223]

[0224] Traction coefficient C D Represented as:

[0225]

[0226] In the formula, b1 = exp(2.3288 - 6.4581φ + 2.4486φ). 2 ); b2=0.0964+0.5565φ; b3=exp(4.905-13.8944φ+18.4222φ 2 -10.2599φ 3 ); b4=exp(1.4681+12.2584φ-20.7322φ 2 +15.8855φ 3 The expression for the relative Reynolds number Re is as follows:

[0227]

[0228] In the formula, d p μ represents the particle diameter; μ represents the viscosity of the continuous phase molecules; φ represents the particle shape factor.

[0229] The particle-wall collision model is as follows:

[0230]

[0231] In the formula, u p1 and v p1 Represents the normal and tangential velocity components before particle collision; u p2 and v p2 This represents the normal and tangential velocity components after a particle collision.

[0232] S3-3: Based on the erosion distribution, the erosion wear distribution results on the valve core surface are obtained.

[0233] Solid particles are uniformly injected into the inlet face in the normal direction, with the particle injection velocity being the same as the inlet fluid velocity. The solid particle material is Fe2O3, with a density of 5240 kg / m³. 3The Mohs hardness is 5.5. The discrete phase model boundaries at the inlet and outlet are defined as escape; the wall surface is defined as reflect. The number of particles incident on the model has a significant impact on the calculation of the erosion rate; insufficient particle tracking may lead to large calculation errors. Therefore, to ensure the accuracy of the erosion prediction results, the independence of particle number needs to be verified. This paper tracks seven particle numbers (2000, 6000, 10000, 20000, 40000, 60000, and 100000) and obtains the curve of the maximum erosion rate on the bottom surface of the valve core versus the number of particles, as shown below. Figure 5 As shown. From Figure 5 As can be seen, when the number of tracked particles reaches 20,000, the maximum erosion rate of the bottom surface of the valve core tends to stabilize, indicating that the numerical calculation results are no longer related to the change in the number of particles.

[0234] Erosion wear rate is not an inherent property of materials, but rather the result of the combined effects of multiple factors. The main factors affecting erosion wear include valve opening degree, particle size, shape factor, and concentration.

[0235] The erosion wear distribution under different working conditions was obtained, compared and analyzed, and the influencing patterns were summarized.

[0236] like Figure 6 The figure shows the erosion wear distribution on the valve core surface under different valve opening degrees: erosion mainly occurs at the valve core edge near the throttling window facing the outlet pipe, and the erosion area increases with the increase of the valve opening degree. The maximum erosion rate on the valve core surface shows a trend of first decreasing, then increasing, and then decreasing again with the increase of the valve opening degree, reaching a minimum value of 1.07 × 10⁻⁶ at 35% opening degree. -5 kg / (m 2 ·s), reaching a maximum value of 2.31×10 at 70% opening. -4 kg / (m 2 The daily erosion rate (·s) is approximately 21 times that at 35% opening. Unlike the trend of the maximum erosion rate, the daily erosion rate on the valve core surface increases continuously with the increase of valve opening.

[0237] like Figure 7 The figure shows a valve opening of 70% and a particle concentration of 1×10⁻⁶. -7 Under the condition of a particle shape factor of 1, the erosion wear distribution on the valve core surface under different particle sizes is as follows: When the particle size is small, erosion is mainly concentrated on the valve core edge near the throttling window facing the outlet pipe. As the particle size increases, the erosion area gradually expands to both sides. The maximum erosion rate and daily erosion amount on the valve core surface show a trend of first increasing and then decreasing with the increase of particle size, both reaching a peak at 30 μm. The maximum erosion rate at 30 μm is about 20 times that at 120 μm, and the daily erosion amount is about 3 times that at 120 μm.

[0238] like Figure 8 The figure shows a valve opening of 70%, a particle size of 30 μm, and a particle concentration of 1 × 10⁻⁶. -7 Under the condition of different particle shape factors, the erosion wear distribution on the valve core surface is as follows: As the shape factor decreases, the erosion area on the bottom surface of the valve core gradually changes from being concentrated near the throttling window facing the outlet pipe to being dispersed near the edges of the four throttling windows. The maximum erosion rate and daily erosion amount on the valve core surface show a trend of first increasing, then decreasing, and then increasing again as the particle shape factor decreases. The maximum erosion rate and daily erosion amount reach their maximum values ​​when the particle shape factor is 0.9, which are 4.04 × 10⁻⁶ and 4.04 × 10⁻⁶, respectively. -4 kg / (m 2 ·s) and 1.09×10 -4 The maximum erosion rate is 2.99 × 10⁻⁶ kg, which is achieved when the particle shape factor is 0.3. -4 kg / (m 2 The daily erosion rate (·s) is approximately 0.074 when the particle shape index is 0.9. The daily erosion rate reaches its minimum value of 4.31 × 10⁻⁶ when the particle shape index is 0.4. -5 kg, approximately 0.4 when 0.9.

[0239] like Figure 9 The figure shows a valve opening of 70%, a particle size of 30 μm, and a particle concentration of 1 × 10⁻⁶. -7 Under the condition of different particle concentrations, the erosion wear distribution on the valve core surface is as follows: the erosion distribution on the valve core surface remains basically unchanged under different particle concentrations, and is concentrated at the edge of the valve core. The maximum erosion rate and daily erosion amount on the valve core surface are both directly proportional to the particle concentration.

[0240] To quantify the influence of four factors—control valve opening, particle size, particle shape coefficient, and particle concentration—on the valve core surface, a four-factor, four-level orthogonal experimental scheme was developed. The maximum erosion rate of the control valve core surface was selected as the evaluation index, and 16 sets of experimental data were designed, as shown in Table 8. Based on the orthogonal experimental data in the table, grey relational analysis (GRA) was used to analyze the influence of these four factors on the erosion wear of the control valve core.

[0241] Table 8 Orthogonal Experiment Data

[0242]

[0243] Grey relational analysis was used to quantify the influence of valve opening, particle size, particle shape factor, and particle concentration on the erosion wear of the control valve core.

[0244] Determine the reference sequence and comparison sequence: Using the maximum erosion rate of the control valve core surface as the reference sequence Y, and factors such as valve opening degree as the comparison sequence X, they are respectively expressed as:

[0245]

[0246]

[0247] In the formula: n is the number of sample points.

[0248] Normalization of variables: To eliminate the influence of differences in units and orders of magnitude among factors, the data is normalized using the mean method.

[0249]

[0250]

[0251] Calculate the grey relational coefficient: First, calculate the absolute value of the difference between each factor sequence after normalization and the reference sequence; then calculate the grey relational coefficient between the comparison sequence and the reference sequence.

[0252]

[0253]

[0254] Calculating the grey relational degree: For each reference sequence, the average of its relational coefficients is the relational degree.

[0255]

[0256] In the formula, i = 1, 2, 3, 4; , ρ represents the minimum and maximum absolute values ​​of all differences; ρ is the resolution coefficient, which is 0.5.

[0257] like Figure 10 The figure shows the correlation degrees corresponding to different factors calculated by grey relational analysis. The grey relational degree ranges from 0 to 1; the closer the value is to 1, the more significant the influence of the factor on the maximum erosion rate of the valve core. Figure 10It can be seen that the factor with the highest correlation to the erosion characteristics of the control valve core is particle concentration, with a gray correlation coefficient of 0.7555, indicating that changes in particle concentration have the greatest impact on the maximum erosion rate of the control valve core. Particle size and valve opening also have a strong influence, with gray correlation coefficients of 0.6871 and 0.6751, respectively. The particle shape coefficient has the lowest gray correlation coefficient, at 0.6197, indicating that changes in the particle shape coefficient have the least impact on the maximum erosion rate of the control valve core compared to the other three factors. Therefore, in practical applications, particle concentration, particle size, and valve opening should be the focus to effectively reduce the erosion problem of the control valve core.

[0258] Although embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are merely illustrative and do not constitute a limitation of the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of protection of the present invention without departing from the principles and spirit of the present invention.

[0259] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0260] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for analyzing the erosion characteristics of turbine control valves based on the modified Oka erosion model, characterized by: Includes the following steps: S1: Oka erosion model parameter correction: S1-1: Establish the explicit basic dynamic equations and construct a three-dimensional model of single-particle impact including particles and valve core; S1-2: Set the material properties of the particles and valve core, mesh the single-particle impact three-dimensional model, and set boundary conditions and loads in combination with working parameters to obtain a calculable finite element model; S1-3: Based on the finite element model, perform explicit dynamic finite element simulation analysis to calculate the volume of the pits on the valve core surface under different working conditions; S1-4: Using the pit volume under the benchmark working condition as a benchmark, analyze the correlation between particle size, impact velocity and impact angle and erosion rate. Based on this, correct the parameters of the Oka erosion model to obtain the corrected Oka erosion model and send it to step S3. S2: Flow field characteristic analysis: S2-1: Establish a fluid dynamics mechanism model and extract the geometric structural features of the turbine control valve cavity to construct a three-dimensional solid model including the valve body, valve core, valve stem, valve cage, and valve cover. S2-2: Based on the three-dimensional solid model, the flow channel of the valve cavity is extracted to obtain the fluid domain geometric model of the regulating valve; S2-3: Mesh the fluid domain geometric model, set the material properties and flow boundary conditions of the steam, and thus establish a solvable numerical model of the flow field; S2-4: Based on the numerical model of the flow field, perform finite volume method simulation analysis, simulate and calculate the velocity field and pressure field distribution in the flow field, obtain the velocity field and pressure field distribution data in the flow field, and send the flow field analysis results to step S3; S3: Erosion Characteristics Analysis: S3-1: Receive the modified Oka erosion model output from step S1 and the flow field analysis results output from step S2, and introduce the erosion wear theory and the modified Oka erosion model based on the flow field analysis results. S3-2: Set solid particle parameters and perform coupled calculations with the flow field to solve the particle motion equation and particle-wall collision model, thereby obtaining the erosion distribution generated during the operation of the control valve. S3-3: Based on the erosion distribution, the erosion wear distribution results on the valve core surface are obtained.

2. The method for analyzing the erosion characteristics of turbine regulating valves based on the modified Oka erosion model according to claim 1, characterized in that: The specific steps for establishing the explicit fundamental dynamic equations in S1-1 are as follows: mass conservation equation: ； In the formula, ρ0 is the initial density of the current volume of the region; V0 is the initial volume of the current volume of the region; m is the current mass corresponding to the current volume of the region; V is the current volume of the region; Momentum conservation equation: ； In the formula, ρ is the density; , , Acceleration in the x, y, and z directions, respectively; For stress tensor; Energy conservation equation: ； In the formula, For strain tensor; For energy; The original formula for the Oka erosion model is: ； ； ； In the formula, E(θ) represents the erosion rate; f(θ) represents the impact angle function; E 90 The value represents the reference erosion rate at an impact angle of 90°; K is a particle property constant, K1 is the hardness index factor, K2 is the velocity index factor, and K3 is the particle size index factor, where... In the simulation, they are combined into a single wear constant; v, v', D, and D' represent the velocity, reference velocity, particle size, and reference particle diameter in the experiment, respectively; Hv is the Vickers hardness of the material.

3. The method for analyzing the erosion characteristics of turbine regulating valves based on the modified Oka erosion model according to claim 2, characterized in that: The material properties in S1-2 include the density, Young's modulus, Poisson's ratio, and specific heat at constant pressure of the particles, as well as the density, Young's modulus, Poisson's ratio, coefficient of linear expansion, yield stress, and tangential modulus of the valve core. The operating parameters include particle size, impact velocity, and impact angle. The number of meshes was determined by mesh independence verification, and the convergence criterion was that the maximum deformation change of the valve core target material was less than 0.1%.

4. The method for analyzing the erosion characteristics of turbine regulating valves based on the modified Oka erosion model according to claim 3, characterized in that: The specific boundary conditions and loads set in S1-2 are as follows: the lower surface of the valve core is used as a fixed constraint; the friction between the solid particles and the valve core is described by a penalty function, and the Coulomb friction coefficient is 0.

25. The penalty function is expressed as: ； In the formula, F n For contact force; k n For contact stiffness; x p This refers to the penetration amount.

5. The method for analyzing the erosion characteristics of turbine regulating valves based on the modified Oka erosion model according to claim 4, characterized in that: The calculation of the pit volume on the valve core surface under different operating conditions in S1-3 is specifically as follows: When a particle impacts the valve core at a 90° angle, the morphology of its pit is relatively regular, and it can be calculated by the pit radius and depth; when a particle impacts the valve core at other angles, the pit often has an irregular shape, so it can be characterized by plastic work. Calculation of pit volume: ； In the formula, V is the volume of the pit; d is the diameter of the pit; and h is the depth of the pit.

6. The method for analyzing the erosion characteristics of turbine regulating valves based on the modified Oka erosion model according to claim 5, characterized in that: The parameter correction in S1-4 specifically includes: Particle size parameter correction: ； In the formula, V D D is the pit volume; D is the particle size; D' is the reference particle size. Impact velocity parameter correction: ； In the formula, V v v is the pit volume; v' is the particle impact velocity; v' is the particle reference impact velocity. Impact angle parameter correction: ； In the formula, V θ θ is the pit volume; θ is the particle impact angle; Hv is the Vickers hardness of the material. The modified Oka erosion model expression is as follows: The erosion rate of the valve core surface is related to the particle size, impact velocity, impact angle, and its own material properties. Combining equation (9-11), the wear rate of a unit mass of particles impacting the valve core surface is: ； In the formula, E is the erosion rate per unit mass of solid particles; ρ0 is the density of the valve core material; ρ is the particle density. Substituting into formula (9-11), the combined erosion rate is: 。 7. The method for analyzing the erosion characteristics of turbine regulating valves based on the modified Oka erosion model according to claim 6, characterized in that: The specific mechanism model for establishing fluid mechanics in S2-1 is as follows: mass conservation equation: ； In the formula, ρ represents density; t represents time; Represents the velocity vector; Momentum conservation equation: ； In the formula, u, v, and w represent the velocity components in the x, y, and z directions, respectively; τ xx , τ xy , τ xz F represents the component of the viscous stress on the surface of the infinitesimal element; p represents the pressure on the infinitesimal element; x F y F z This represents the force acting on a infinitesimal element; Energy conservation equation: ； In the formula, T represents temperature; k represents the fluid heat transfer coefficient; c P S represents specific heat capacity. T Represents the viscous dissipation term; Turbulence model: ； ； ； In the formula, ; ; ; ; ; ; ; .

8. The method for analyzing the erosion characteristics of turbine regulating valves based on the modified Oka erosion model according to claim 7, characterized in that: In S2-3, the material properties of the steam include density, specific heat capacity, thermal conductivity, viscosity, and molecular weight; Flow boundary conditions include inlet pressure, inlet temperature, turbulence model parameters, and wall conditions; The mesh generation method uses a polyhedral core volume mesh to refine the throttling window and valve core region. The mesh number is determined by verifying mesh independence and using the outlet flow rate change of less than 0.1% as the convergence criterion.

9. The method for analyzing the erosion characteristics of turbine regulating valves based on the modified Oka erosion model according to claim 8, characterized in that: In step S3-2, the solid particle parameters include particle size, particle shape factor, and particle concentration; the particle motion equation is: ； In the formula, m p Indicates particle mass; Indicates particle velocity; ρ represents fluid velocity. p ρ represents particle density; ρ represents fluid density. It represents the sum of additional forces such as Saffman lift, Magnus lift, and pressure gradient force; The relaxation time of a particle is expressed as follows: ； Traction coefficient C D Represented as: ； In the formula, b1 = exp(2.3288 - 6.4581φ + 2.4486φ). 2 ); b2=0.0964+0.5565φ; b3=exp(4.905-13.8944φ+18.4222φ 2 -10.2599φ 3 ); b4=exp(1.4681+12.2584φ-20.7322φ 2 +15.8855φ 3 The expression for the relative Reynolds number Re is as follows: ； In the formula, d p μ represents the particle diameter; μ represents the continuous phase molecular viscosity; φ represents the particle shape factor. The particle-wall collision model is as follows: ； In the formula, u p1 and v p1 Represents the normal and tangential velocity components before particle collision; u p2 and v p2 This represents the normal and tangential velocity components after a particle collision.

10. The method for analyzing the erosion characteristics of turbine regulating valves based on the modified Oka erosion model according to claim 9, characterized in that: Specifically, S3-3 is: Grey relational analysis was used to quantify the influence of valve opening, particle size, particle shape factor, and particle concentration on the erosion wear of the control valve core. Determine the reference sequence and comparison sequence: Using the maximum erosion rate of the control valve core surface as the reference sequence Y, and factors such as valve opening degree as the comparison sequence X, they are respectively expressed as: ； ； In the formula: n is the number of sample points; Normalization of variables: To eliminate the influence of differences in units and orders of magnitude among factors, the data is normalized using the mean method. ； ； Calculate the grey relational coefficient: First, calculate the absolute value of the difference between each factor sequence after normalization and the reference sequence; then calculate the grey relational coefficient between the comparison sequence and the reference sequence. ； ； Calculating the grey relational degree: For each reference sequence, the average of its relational coefficients is the relational degree. ； In the formula, i = 1, 2, 3, 4; , These are the minimum and maximum absolute values ​​of all differences; ρ is the resolution coefficient, which is set to 0.5.

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