Boundary condition optimization method for flow-induced vibration simulation of heat transfer pipe of steam generator

Abstract

The invention provides a boundary condition optimization method and system for flow-induced vibration simulation of a heat transfer pipe of a steam generator. The method comprises the following steps: establishing a local rod bundle unit model comprising a straight pipe section and a bent pipe section of the heat transfer pipe; performing first flow field simulation on the straight pipe section to obtain flow field parameters of the top outlet section of the straight pipe section; the bottom of the bent pipe section is set as a secondary loop inlet, and the top of the bent pipe section is set as a secondary loop pressure outlet; on the basis of the flow field parameters, after non-uniform boundary conditions of a secondary loop inlet of the bent pipe section are determined, second flow field simulation is conducted on the bent pipe section, so that fluid acting force acting on the heat transfer pipe is obtained; and performing structural dynamics analysis on the heat transfer tube based on the fluid acting force to obtain a vibration effect result of the heat transfer tube. According to the method, the limitation that the inlet of the bent pipe section is simplified into a symmetrical boundary or a uniform inlet in a traditional model is broken through, and the complex characteristics of the bent pipe section can be reproduced more truly, so that more accurate flow excitation input is provided for flow-induced vibration analysis.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flow-induced vibration analysis of nuclear power plant steam generator heat transfer tubes, in particular to a boundary condition optimization method and system for improving the simulation authenticity of flow-induced vibration of inverted U-shaped heat transfer tubes, and is especially suitable for numerical simulation considering the cross action of secondary loop fluid on the elbow section of the heat transfer tube. BACKGROUND

[0002] The steam generator (SG) is an important barrier between the primary and secondary loops to prevent the release of radioactive fission products into the environment and a heat transfer device. Its reliability is related to the stability of the operation of the nuclear power system. The heat transfer tube, as a key component in the steam generator, is the pressure boundary and heat transfer boundary of the primary loop in the nuclear power system, and needs to withstand the scouring of the high-temperature and high-pressure fluid with high radioactivity on the primary side and the complex two-phase flow heat transfer on the secondary side. This will cause the heat transfer tube to vibrate, and the flow-induced vibration phenomenon will bring about fatigue, wear and tear, etc. The problem is prone to cause the thinning and even rupture of the tube wall (SGTR), which threatens the safety of the operation of the nuclear power plant unit. Due to the narrow working space in the steam generator, the thin wall of the heat transfer tube, the large number of tubes and their distribution inside the steam generator cavity, it is difficult to detect the operating performance, the processing and assembly state and the local fretting wear state of the heat transfer tube. Therefore, accurately analyzing the flow-induced vibration characteristics of the heat transfer tube is of great significance for preventing wear and tear, optimizing the design of the steam generator and safety evaluation.

[0003] Due to the large size, complex structure, numerous components, and high cost of steam generators, and their operation under high temperature and pressure conditions, current research methods for flow-induced vibration of heat transfer tubes mainly fall into two categories: experimental research and numerical simulation. In experimental research, visualized or controllable two-phase flow reduced-ratio tube bundle experimental rigs are constructed to observe and analyze the flow-induced vibration characteristics of heat transfer tubes: measuring the tube bundle vibration effects under different flow velocities and void ratios; and studying the frequency domain characteristics of gas-liquid two-phase flow excitation. However, experimental methods often struggle to reproduce the complex flow fields and load constraints within actual steam generators, and suffer from high costs, long development cycles, and significant measurement limitations. Numerical simulation methods, due to their ability to reproduce complex fluid-solid-thermal multi-physics couplings and ease of parameterization, have gradually become an important tool for studying flow-induced vibration of heat transfer tubes in steam generators. Porous media methods are often used to simulate the overall flow state of the secondary loop in steam generators. While they can reflect the basic characteristics of flow and heat transfer at a macroscopic level, their simulation accuracy is relatively limited for local flow details directly related to the flow-induced vibration mechanism, such as crossflow between tubes, vortex structure evolution, and turbulent fluctuations. To more accurately capture the fluid-structure-thermal coupling mechanism between tube bundles, a refined modeling method based on local bar bundle elements is adopted. This method involves constructing a local computational domain that reflects typical tube bundle arrangements, thereby achieving higher-precision simulation of complex flow field details between tubes. This allows for a more realistic revelation of the coupling mechanism between flow excitation and tube bundle vibration, providing an effective tool for in-depth analysis of flow-induced vibration.

[0004] However, while existing numerical simulation studies consider the thermal coupling between the primary and secondary sides in flow calculations, their vibration response analyses only consider the excitation from the two-phase flow in the two-loop system, failing to account for the lateral scouring effect of the secondary fluid on the heat transfer tubes within the bend region and its actual impact on the tube structure's dynamic behavior. In reality, as the secondary fluid flows through the bend, the combined effect of the change in flow direction and the lateral sweeping effect creates a continuous and non-uniform hydrodynamic load on the heat transfer tube surface. This load not only affects the local stress state of the pipe but may also further influence the overall deformation, vibration modes, and contact wear behavior between the heat transfer tubes and the supporting structure by altering the system's equivalent stiffness and damping characteristics. Ignoring this effect leads to an incomplete understanding of the source of flow-induced vibration excitation in the bend section, biased predictions of vibration response and wear location, and consequently affects the accuracy of the steam generator integrity assessment.

[0005] In view of this, the present invention provides a boundary condition optimization method for simulating flow-induced vibration of heat transfer tubes in steam generators. The aim is to develop a fluid-structure interaction simulation method that can more realistically reflect the lateral scouring effect of secondary fluid on the inverted U-shaped heat transfer tube bend, so as to improve the credibility of flow-induced vibration and wear analysis of heat transfer tubes and provide a more reliable theoretical and technical basis for the safe design and operation and maintenance of steam generators. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for optimizing boundary conditions in simulating flow-induced vibration of heat transfer tubes in steam generators.

[0007] A boundary condition optimization method for simulating flow-induced vibration of a steam generator heat transfer tube, provided by the present invention, includes: Step S1: Establish a local rod bundle element model including straight and curved sections of heat transfer tubes; Step S2: Perform a first flow field simulation on the straight pipe section to obtain the flow field parameters of the top outlet section of the straight pipe section; set the bottom of the bend section as the secondary loop inlet and the top of the bend section as the secondary loop pressure outlet; Step S3: Based on the flow field parameters, determine the non-uniform boundary conditions at the secondary loop inlet of the bend section; Step S4: Based on the non-uniform boundary conditions, perform a second flow field simulation on the bent pipe section to obtain the fluid force acting on the heat transfer pipe; Step S5: Based on the fluid force, perform structural dynamics analysis on the heat transfer tube to obtain the vibration effect results of the heat transfer tube.

[0008] Preferably, the flow field parameters include spatial distribution data of at least one of flow velocity, temperature, and cavitation rate.

[0009] Preferably, the step of determining the non-uniform boundary conditions includes: The flow field parameters are fitted with a function in the lateral direction to generate a non-uniform distribution function describing the spatial distribution of the flow field parameters, and the non-uniform distribution function is used as the non-uniform boundary condition.

[0010] Preferably, the local bar bundle unit model further includes a wall for defining the secondary loop flow channel, and when performing a second flow field simulation on the bend section, the wall except for the secondary loop inlet and the secondary loop pressure outlet is set as a symmetric boundary condition.

[0011] Preferably, the first flow field simulation and / or the second flow field simulation are performed using a two-fluid model.

[0012] Preferably, the vibration effect results include at least one of the vibration displacement, velocity, acceleration of the heat transfer tube, and contact force with the supporting structure.

[0013] Preferably, the method further includes: The hot end of the heat transfer tube is set as the primary loop inlet, and the cold end of the heat transfer tube is set as the primary loop pressure outlet.

[0014] A boundary condition optimization system for simulating flow-induced vibration of a steam generator heat transfer tube, provided by the present invention, includes: Module M1: Establish a local rod bundle element model including straight and curved sections of heat transfer tubes; Module M2: Performs a first flow field simulation on the straight pipe section to obtain the flow field parameters of the top outlet section of the straight pipe section; sets the bottom of the bend section as the secondary loop inlet and the top of the bend section as the secondary loop pressure outlet; Module M3: Based on the flow field parameters, determine the non-uniform boundary conditions at the secondary loop inlet of the bend section; Module M4: Based on the non-uniform boundary conditions, perform a second flow field simulation on the bend section to obtain the fluid forces acting on the heat transfer tube; Module M5: Based on the fluid forces, perform structural dynamics analysis on the heat transfer tube to obtain the vibration effect results of the heat transfer tube.

[0015] Preferably, the flow field parameters include spatial distribution data of at least one of flow velocity, temperature, and cavitation rate; The first flow field simulation and / or the second flow field simulation are calculated using a two-fluid model; The vibration effect results include at least one of the following: vibration displacement, velocity, acceleration of the heat transfer tube, and contact force with the supporting structure.

[0016] Preferably, the local bar bundle unit model further includes a wall for defining the secondary loop flow channel, and when performing a second flow field simulation on the bend section, the wall except for the secondary loop inlet and the secondary loop pressure outlet is set as a symmetric boundary condition. The system further includes: setting the hot end of the heat transfer tube as a primary loop inlet and the cold end of the heat transfer tube as a primary loop pressure outlet.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention overcomes the limitations of traditional models that simplify the inlet of the bend section to a symmetrical boundary or a uniform inlet by setting the bottom of the bend section as the secondary loop inlet, the top as the secondary loop pressure outlet, and the remaining wall surfaces as symmetrical boundaries. This boundary condition configuration physically better matches the actual flow path and lateral sweeping characteristics of the secondary fluid in the bend region from bottom to top, and can more realistically reproduce the complex lateral scouring flow field, vortex structure evolution, and turbulent pulsation characteristics of the bend section, thus providing a more accurate flow excitation input for flow-induced vibration analysis.

[0018] 2. This invention constructs the boundary conditions at the inlet of the bend section by extracting flow parameters (velocity, temperature, and cavitation rate) from the top of the straight pipe section and fitting them in the spatial direction, rather than simply assuming a uniform or symmetrical distribution. This method ensures the continuity of local flow development, enabling the inlet conditions of the bend section to reflect the actual flow situation in the upstream straight pipe section, avoiding errors introduced by idealized boundary conditions, and enhancing the coherence and reliability of the flow field simulation throughout the computational domain.

[0019] 3. This invention considers both the turbulent excitation force generated by the two-phase crossflow on the secondary side and the steady-state radial pressure generated by the centrifugal inertial effect of the primary side fluid in the bend section during vibration analysis. In particular, by optimizing the boundary conditions to realistically simulate the crossflow effect of the secondary side on the bend section, it can more accurately assess the comprehensive influence of the fluid load in this region on the overall deformation, vibration modes, and contact behavior with the supporting structure of the heat transfer tube. This helps to more completely understand the source of vibration excitation, especially clarifying the contribution of the secondary side crossflow to the vibration of the bend section.

[0020] 4. The more realistic flow field and structural response obtained by this method can more accurately predict the contact force, fretting slip distance and wear depth distribution between the heat transfer tube and the support plate. In particular, it can explain and predict the phenomenon that the wear signals observed in actual power plant overhauls are mostly concentrated on the cold end support plate.

[0021] 5. This invention uses local rod bundle elements for refined simulation and employs physically realistic boundary conditions in the bend section region. This captures necessary flow details and vibration characteristics while avoiding the enormous computational burden of full-scale steam generator models. The unidirectional fluid-structure interaction framework and parameter fitting method used have a clear process and are easy to implement on existing CFD and dynamic analysis software platforms, demonstrating good engineering applicability and promotional value. Attached Figure Description

[0022] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1a This is a schematic diagram of the boundary conditions for the pre-optimized rod bundle element model of this invention.

[0023] Figure 1b This is a schematic diagram of the boundary conditions for the optimized heat transfer tube bundle model of the present invention.

[0024] Figure 2 The image shows a comparison of the lateral vortex simulation between the traditional symmetrical boundary and the bend section of the present invention.

[0025] Figure 3 This is a simulated deformation diagram of the heat transfer tube under optimized boundary conditions according to the present invention.

[0026] Figure 4 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0027] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0028] This invention significantly improves the realism of the simulation of the secondary loop fluid sweeping across the bend of the heat transfer tube by setting the bottom of the inverted U-shaped heat transfer tube bend section as the secondary loop inlet, the top as the secondary loop pressure outlet, and the remaining wall surfaces as symmetrical boundaries, and by fitting the inlet parameters of the bend section with the flow data of the straight pipe section. This can be used to more accurately predict the flow-induced vibration response, contact wear location and wear mechanism of the heat transfer tube, and provide technical support for the safe operation and maintenance of steam generators.

[0029] Example 1 According to the present invention, a boundary condition optimization method for simulating flow-induced vibration of heat transfer tubes in a steam generator is provided, such as... Figure 4 As shown, it includes: Step 1: Establish the geometric model. Based on the actual structure of the steam generator, construct a local rod bundle unit model of the primary loop flow channel, secondary loop flow channel, and heat transfer tube entities. The straight section length of the inverted U-shaped heat transfer tube is 9.8m, the inner diameter of the heat transfer tube is 15.44mm, the wall thickness is 1.02mm, the tube spacing is 24.89mm, and the bend radius is 100mm.

[0030] Step 2: Set boundary conditions. The primary loop fluid flows inside the inverted U-shaped heat transfer tube, with the hot end of the heat transfer tube set as the primary loop inlet and the cold end set as the primary loop pressure outlet; the secondary loop fluid flows from bottom to top outside the tube, including the inlet of the straight pipe section and the inlet of the bend section, with the bottom of the bend section set as the secondary loop inlet and the top of the bend section set as the secondary loop pressure outlet, and the remaining wall surfaces set as symmetrical boundary conditions.

[0031] Step 3: Obtain the secondary loop inlet parameters. This is done by analyzing the velocity, temperature, and cavitation rate distribution at the top of the straight pipe section, and then... x , z The flow direction was fitted to construct boundary conditions for the bend section that better conform to the characteristics of the secondary loop flow. Specifically, the parameters of the steady-state calculation results of the top region of the straight pipe section were extracted and fitted to obtain the parameter input of the secondary side inlet of the bend section in the optimization model. The fitting process was carried out in the z-direction and x-direction respectively, and the results are shown in Equation (1).

[0032] (1) In the formula, Temperature input in the z-direction; Input the velocity in the z-direction; Input the void ratio in the z-direction; Temperature input in the x-direction; Input the velocity in the x-direction; Input the voiding rate in the x-direction.

[0033] The primary loop flow rate was extracted based on the flow field simulation results of the primary loop lower head. Simultaneously, the primary loop inlet temperature and the secondary loop straight pipe inlet flow rate and temperature were averaged based on nuclear power plant operating parameters. Specific data are as follows: primary loop inlet flow rate 2.33 kg / s, primary loop inlet temperature 594 K, primary loop outlet pressure 15.5 MPa; secondary loop straight pipe inlet flow rate 0.28 kg / s, secondary loop straight pipe inlet temperature 499 K, secondary loop outlet pressure 5.6 MPa.

[0034] Step 4: Perform flow field simulation. Based on the above boundary conditions, computational fluid dynamics (CFD) software is used to simulate the flow field. The secondary loop fluid absorbs heat from the primary loop and undergoes two-phase boiling heat transfer. A two-fluid model is used to describe its physical process, with the vapor and liquid phases treated as independent continuous media, satisfying the continuity, momentum, and energy equations respectively.

[0035] Continuity equation:

[0036] Momentum equation: Energy equation: (4) In the formula: , , , , , , , Represent Volume fraction and density of the phase (liquid or vapor phase) ,speed, ,pressure, Viscosity enthalpy value ,temperature, Thermal conductivity ; Representing unit volume Facing each other The mass rate of phase transfer ; represent Phase is transmitted through the phase interface to The heat of the phase, ; Represents interaction forces. The turbulence characteristics of the flow field are determined using standard... Model characterization: Considering the additional disturbances caused by the second-loop bubbles, the liquid-phase turbulent viscosity coefficient was further calculated using the Sato-enhanced turbulence model. Interphase heat and momentum transfer were characterized using the Two-resistance model and the Ishii-Zuber model, respectively.

[0037] Step 5: Extract fluid forces. Extract the fluid forces inside and outside the heat transfer tube from the flow field simulation results.

[0038] Step 6: Conduct structural dynamics analysis: Apply the extracted fluid dynamic pressure as a load to the finite element model of the inverted heat transfer pipe, calculate its vibration effect, and output the vibration results.

[0039] In the complex two-phase flow environment of a steam generator, the total pressure of the flow field can be considered as the sum of static and dynamic pressures. Considering that at a certain cross-section of the heat transfer tube, the static pressure typically exhibits strong anisotropic symmetry, and the resultant force of the static pressure exerted on the tube wall is approximately zero, this paper focuses only on the contribution of dynamic pressure to the excitation force on the heat transfer tube. To simplify the analysis, the interfacial forces and momentum exchange processes between the vapor and liquid phases are ignored. Based on the principle of energy conservation, the formula for calculating the multiphase flow pressure is derived as follows: (2) In the formula, For mixed fluid dynamic pressure; This refers to the liquid phase cavitation rate; The density of the liquid phase; The apparent flow rate of the liquid phase; This refers to the vapor phase cavitation rate; This is the density of the vapor phase; The apparent velocity of the vapor phase.

[0040] This method ignores the viscous forces of the flow field on the heat transfer tube and the pressure fluctuations caused by multiphase flow, and only considers the effect of the fluid normal velocity component on the tube wall. Therefore, the dynamic pressure formed by the component of the velocity vector pointing towards the heat transfer tube wall is defined as the effective impact dynamic pressure, which serves as an approximate index for evaluating local excitation force.

[0041] like Figure 1a and Figure 1b The diagram shown is a schematic diagram of the boundary conditions of the optimized rod bundle unit model according to an embodiment of the present invention. Compared with the traditional rod bundle unit model which is set to symmetrical boundary conditions, the present invention sets the bottom of the bend section as the second-loop inlet, the top of the bend section as the second-loop pressure outlet, and the remaining wall surfaces as symmetrical boundary conditions.

[0042] like Figure 2As shown in the figure, the comparison diagram of the transverse vortex of the conventional symmetry boundary and the bend section of the present invention is presented. The simulation results show that the vortex level at the bend of the optimized rod bundle unit model of the present invention is significantly improved, which more realistically depicts the transverse scouring effect of the secondary side fluid on the bend section.

[0043] like Figure 3 The figure shown is a heat transfer tube deformation diagram under optimized boundary conditions according to an embodiment of the present invention. It more accurately simulates the influence of fluid load in the secondary side region of the bend section on the overall deformation of the heat transfer tube, as well as the analysis of the flow-induced vibration wear mechanism of the heat transfer tube.

[0044] Compared with the prior art, the embodiments of the present invention can more accurately depict the lateral scouring effect of the secondary fluid on the bend section during the actual operation of the steam generator by optimizing the boundary conditions of the inverted U-shaped heat transfer tube bend section.

[0045] Example 2 The present invention also provides a boundary condition optimization system for simulating flow-induced vibration of a steam generator heat transfer tube. The boundary condition optimization system for simulating flow-induced vibration of a steam generator heat transfer tube can be implemented by executing the process steps of the boundary condition optimization method for simulating flow-induced vibration of a steam generator heat transfer tube. That is, those skilled in the art can understand the boundary condition optimization method for simulating flow-induced vibration of a steam generator heat transfer tube as a preferred embodiment of the boundary condition optimization system for simulating flow-induced vibration of a steam generator heat transfer tube.

[0046] A boundary condition optimization system for simulating flow-induced vibration of a steam generator heat transfer tube, provided by the present invention, includes: Module M1: Establishes a local bar bundle element model including straight and curved sections of heat transfer tubes. The local bar bundle element model also includes walls defining the secondary loop flow path, and when simulating the second flow field of the curved section, the walls, except for the secondary loop inlet and the secondary loop pressure outlet, are set as symmetric boundary conditions. Module M2: Performs a first flow field simulation on the straight pipe section to obtain flow field parameters at the top outlet section of the straight pipe section. The flow field parameters include spatial distribution data of at least one of velocity, temperature, and cavitation rate. The bottom of the bend section is set as the secondary loop inlet, and the top of the bend section is set as the secondary loop pressure outlet. Module M3: Based on the flow field parameters, determine the non-uniform boundary conditions at the secondary loop inlet of the bend section; Module M4: Based on the non-uniform boundary conditions, a second flow field simulation is performed on the bend section to obtain the fluid forces acting on the heat transfer pipe. The first flow field simulation and / or the second flow field simulation are calculated using a two-fluid model.

[0047] Module M5: Based on the fluid forces, performs structural dynamics analysis on the heat transfer tube to obtain the vibration effect results of the heat transfer tube. The vibration effect results include at least one of the vibration displacement, velocity, acceleration, and contact force with the supporting structure of the heat transfer tube. The system further includes: setting the hot end of the heat transfer tube as a primary loop inlet and the cold end of the heat transfer tube as a primary loop pressure outlet.

[0048] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0049] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for optimizing boundary conditions to simulate flow-induced vibration in heat transfer tubes of a steam generator, characterized in that, include: Step S1: Establish a local rod bundle element model including straight and curved sections of heat transfer tubes; Step S2: Perform a first flow field simulation on the straight pipe section to obtain the flow field parameters of the top outlet section of the straight pipe section; set the bottom of the bend section as the secondary loop inlet and the top of the bend section as the secondary loop pressure outlet; Step S3: Based on the flow field parameters, determine the non-uniform boundary conditions at the secondary loop inlet of the bend section; Step S4: Based on the non-uniform boundary conditions, perform a second flow field simulation on the bent pipe section to obtain the fluid force acting on the heat transfer pipe; Step S5: Based on the fluid force, perform structural dynamics analysis on the heat transfer tube to obtain the vibration effect results of the heat transfer tube.

2. The boundary condition optimization method for simulating flow-induced vibration of heat transfer tubes in a steam generator according to claim 1, characterized in that, The flow field parameters include spatial distribution data of at least one of flow velocity, temperature, and cavitation rate.

3. The boundary condition optimization method for simulating flow-induced vibration of heat transfer tubes in a steam generator according to claim 1, characterized in that, The step of determining the non-uniform boundary conditions includes: The flow field parameters are fitted with a function in the lateral direction to generate a non-uniform distribution function describing the spatial distribution of the flow field parameters, and the non-uniform distribution function is used as the non-uniform boundary condition.

4. The boundary condition optimization method for simulating flow-induced vibration of heat transfer tubes in a steam generator according to claim 1, characterized in that, The local bar bundle unit model also includes walls for defining the secondary loop flow path, and when performing a second flow field simulation on the bend section, the walls other than the secondary loop inlet and the secondary loop pressure outlet are set as symmetric boundary conditions.

5. The boundary condition optimization method for simulating flow-induced vibration of heat transfer tubes in a steam generator according to claim 1, characterized in that, The first flow field simulation and / or the second flow field simulation are performed using a two-fluid model.

6. The boundary condition optimization method for simulating flow-induced vibration of heat transfer tubes in a steam generator according to claim 1, characterized in that, The vibration effect results include at least one of the following: vibration displacement, velocity, acceleration of the heat transfer tube, and contact force with the supporting structure.

7. The boundary condition optimization method for simulating flow-induced vibration of heat transfer tubes in a steam generator according to claim 1, characterized in that, The method further includes: The hot end of the heat transfer tube is set as the primary loop inlet, and the cold end of the heat transfer tube is set as the primary loop pressure outlet.

8. A boundary condition optimization system for simulating flow-induced vibration of heat transfer tubes in a steam generator, characterized in that, include: Module M1: Establish a local rod bundle element model including straight and curved sections of heat transfer tubes; Module M2: Performs a first flow field simulation on the straight pipe section to obtain the flow field parameters of the top outlet section of the straight pipe section; sets the bottom of the bend section as the secondary loop inlet and the top of the bend section as the secondary loop pressure outlet; Module M3: Based on the flow field parameters, determine the non-uniform boundary conditions at the secondary loop inlet of the bend section; Module M4: Based on the non-uniform boundary conditions, perform a second flow field simulation on the bend section to obtain the fluid forces acting on the heat transfer tube; Module M5: Based on the fluid forces, perform structural dynamics analysis on the heat transfer tube to obtain the vibration effect results of the heat transfer tube.

9. The boundary condition optimization system for simulating flow-induced vibration of a steam generator heat transfer tube according to claim 8, characterized in that, The flow field parameters include spatial distribution data of at least one of flow velocity, temperature and cavitation rate; The first flow field simulation and / or the second flow field simulation are calculated using a two-fluid model; The vibration effect results include at least one of the following: vibration displacement, velocity, acceleration of the heat transfer tube, and contact force with the supporting structure.

10. The boundary condition optimization system for simulating flow-induced vibration of a steam generator heat transfer tube according to claim 8, characterized in that, The local bar bundle unit model also includes walls for defining the secondary loop flow channel, and when performing the second flow field simulation on the bend section, the walls other than the secondary loop inlet and the secondary loop pressure outlet are set as symmetric boundary conditions. The system further includes: setting the hot end of the heat transfer tube as a primary loop inlet and the cold end of the heat transfer tube as a primary loop pressure outlet.

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