A method for reconstructing flow field forces of flow-induced vibration in heat transfer tubes of steam generators

Abstract

A method for reconstructing the flow field force of the heat transfer tube of a steam generator caused by flow-induced vibration is proposed. The method extracts the near-wall area in the three-dimensional flow field data, converts the effective velocity, and calculates the fluid dynamic pressure and fluid viscosity based on multiphase flow. The flow field force on the heat transfer tube is realized after radial synthesis and circumferential synthesis. The invention optimizes the mechanical model of the heat transfer tube by combining the excitation force and the viscosity force, can predict the vibration wear of the heat transfer tube, and has good interpretability of the calculation results.

Description

Technical Field

[0001] The present invention relates to a technology in the field of nuclear reactor control, in particular to a method for reconstructing flow field force of steam generator heat transfer tube flow-induced vibration based on multiphase flow pressure and structural characteristics. Background Art

[0002] The steam generator connects the primary and secondary circuits of a nuclear power plant. If the heat transfer tubes of the steam generator are worn and ruptured due to flow-induced vibration, radioactive substances in the primary circuit will enter the secondary circuit, causing a huge impact on the environment and safety. Therefore, preventing the wear and rupture of the heat transfer tubes of the steam generator is of economic and safety significance. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention proposes a method for reconstructing the flow field force of flow-induced vibration of a heat transfer tube of a steam generator. The method takes into account the characteristics of the single-phase flow on the primary side and the multiphase flow on the secondary side of the steam generator, introduces the multiphase flow pressure and the fluid viscosity to optimize the mechanical model of the heat transfer tube, takes into account the comprehensive effect of the fluid inside and outside the heat transfer tube of the steam generator, takes into account the difference in the structure of the straight tube section and the curved tube section, introduces the concept of effective excitation when calculating the flow field excitation force, calculates the effective excitation force and the viscous force in the unit flow field area, and optimizes the mechanical model of the heat transfer tube by combining the excitation force and the viscous force. This method can realize the prediction of vibration wear of the heat transfer tube and has good interpretability of the calculation results.

[0004] The present invention is achieved through the following technical solutions:

[0005] The present invention relates to a method for reconstructing flow field forces of flow-induced vibration of a heat transfer tube of a steam generator. The method extracts the near-wall area in three-dimensional flow field data, converts the effective velocity, and obtains the fluid dynamic pressure and fluid viscosity based on multiphase flow calculation. The flow field forces acting on the heat transfer tube are realized after radial synthesis and circumferential synthesis.

[0006] Technical Effects

[0007] The present invention considers the multiphase flow pressure characteristics to calculate the flow field exciting force in the analysis and calculation of flow-induced vibration of the steam generator heat transfer tube; combined with the structural characteristics of the U-tube of the heat transfer tube, the concept of effective dynamic pressure is proposed, and the effective exciting force of the heat transfer tube vibration caused by the flow field is calculated in the micro-flow field unit at each position in the flow field space. At the same time, the comprehensive benefits of the primary and secondary sides are integrated. Compared with the prior art, the present invention completes the mechanical analysis of the steam generator heat transfer tube in a multiphase flow environment, calculates the wear caused by the flow-induced vibration of the steam generator heat transfer tube, and provides calculation parameters, and has good interpretability; completes the extraction of the effective dynamic pressure that causes the flow-induced vibration of the heat transfer tube at each position, and realizes transient calculation in the time dimension, and obtains effective dynamic pressure data in multiple dimensions of space and time. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a flow chart of the present invention;

[0009] Figure 2 This is a schematic diagram for judging effective speed;

[0010] Figure 3 Schematic diagram of exciting force at various positions of the heat transfer tube;

[0011] In the figure: (a) is the exciting force at the hot end of the straight pipe section in the x-direction; (b) is the exciting force at the hot end of the straight pipe section in the y-direction; (c) is the exciting force at the cold end of the straight pipe section in the x-direction; (d) is the exciting force at the cold end of the straight pipe section in the y-direction; (e) is the exciting force at the curved pipe section in the x-direction. DETAILED DESCRIPTION

[0012] like Figure 1 As shown, this embodiment involves a method for reconstructing the flow field force of steam generator heat transfer tube flow-induced vibration based on multiphase flow pressure and structural characteristics, including: division of heat transfer pipelines and flow field space areas; calculation of effective dynamic pressure; synthesis of effective dynamic pressures inside and outside the tube and at various positions in the space.

[0013] Step 1: Divide the flow field simulation data to be processed into straight pipe sections and curved pipe sections, inside of the pipe and outside of the pipe according to the regions.

[0014] The flow field simulation data to be processed include: flow field unit area coordinates, density, cavitation rate, temperature, velocity, and pressure.

[0015] Step 2: After discretizing the data after the division, the unit area coordinates of the flow field are converted into a polar coordinate system, and the near-wall area of ​​the heat transfer tube is extracted.

[0016] The heat transfer tube near wall area refers to: the area within 0.15mm in the axial direction of the inner and outer tubes of the heat transfer tube.

[0017] Step 3: Determine the extracted effective impact velocity of the heat transfer tube near the wall, that is, the velocity of the flow field unit in the near-wall region that directly generates impact force on the tube wall due to the fluid dynamic pressure, specifically including:

[0018] 3.1 For the straight section and curved section of the U-shaped pipe, the inner side and the outer side of the pipe, the velocity direction of the unit fluid in different areas is used to determine whether it is an effective impact velocity. Specifically, the spatial data of each node is extracted according to the CFD flow field calculation, and divided into the straight section and curved section of the U-shaped pipe, the inner side and the outer side of the pipe. And according to the extracted flow field velocity direction combined with the spatial position area, the velocity in the small area of ​​the flow field is judged to be an effective impact velocity, that is, the velocity pointing to the normal direction of the pipe wall without considering the viscous force of the fluid.

[0019] like Figure 2 As shown, the direction pointing to the normal line of the pipe wall points to the inner wall of the pipe in the flow field area inside the pipe; points to the outer wall of the pipe in the flow field area outside the pipe; in the straight pipe section, the effective impact velocity only exists in the x and y directions; in the curved pipe area, the effective impact velocity exists in the x, y and z directions.

[0020] 3.2 The effective impact velocity is calculated using the fluid dynamic pressure formula, including the calculation of the single-phase flow pressure inside the tube and the calculation of the multiphase flow pressure outside the tube, specifically: Where: α l is the liquid phase cavitation rate, ρ l is the liquid density, U l is the liquid superficial velocity, α v is the vapor phase cavitation rate, ρ v is the vapor phase density, U v is the superficial velocity of the vapor phase.

[0021] 3.3 For the ineffective impact velocity, the viscosity force deviating from the pipeline and the viscosity force parallel to the pipeline are calculated by the fluid viscosity formula, including: single-phase flow in the pipeline and multiphase flow outside the pipeline, specifically: the viscosity force deviating from the pipeline Viscous force parallel to the pipe Where: μ is the multiphase flow viscosity, v n is the normal velocity, v t is the tangential velocity, fluid viscosity μ=α l μ l +α g μ g , μ l is the liquid viscosity, μ v is the vapor phase viscosity.

[0022] Step 4: synthesize the radial and circumferential forces of the pipe to obtain the magnitude and direction of the force at each position of the heat transfer pipe. Specifically, first synthesize the flow field excitation force generated in each circumferential area of ​​the heat transfer pipe, ignoring the torque effect on the pipe; then synthesize the excitation force on the primary and secondary sides of the pipe.

[0023] After specific practical experiments, according to the actual boundary conditions and geometric parameters of the currently operating nuclear power units, the CFD flow field calculation results were obtained through numerical simulation methods, and the exciting forces at various positions of the heat transfer tubes were extracted using this method. Figure 3As shown in the figure, the magnitude of the exciting force at various positions of a U-shaped heat transfer tube under one working condition. Through refined modeling, it can be seen that the exciting force presents different fluctuations and amplitudes in the straight section of the heat transfer tube. In the inlet area, it is mainly controlled by density, and the fluctuation presents a large amplitude range. In the curved section, due to the influence of the curved structure, the exciting force shows a more obvious directional difference. Comparing the straight section area of ​​the hot end and the cold end of the U-shaped heat transfer tube, the exciting force at the cold end has obvious directionality due to the influence of the curved section structure, and the absolute value is also much larger than that at the hot end. This can explain the phenomenon that the wear of the heat transfer tube at the cold end is greater than that at the hot end in actual production.

[0024] Compared with the existing technology, this method combines the multiphase flow characteristics and the geometric structure of the heat transfer tube to achieve multi-dimensional and refined modeling of the flow field excitation force at various positions of the heat transfer tube, and the results have good interpretability.

[0025] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. A method for reconstructing flow field force of flow-induced vibration of heat transfer tubes of steam generators, characterized in that: By extracting the near-wall area in the three-dimensional flow field data and converting the effective velocity, the fluid dynamic pressure and fluid viscosity force are calculated based on the multiphase flow, and the flow field force on the heat transfer tube is realized after radial synthesis and circumferential synthesis. The effective speed conversion is: 3.1 For the straight section and curved section, the inside and outside of the U-shaped pipe, the velocity direction of the unit fluid in different areas is used to determine whether it is an effective impact velocity. Specifically, the spatial data of each node is extracted according to the CFD flow field calculation, and divided into the straight section and curved section, the inside and outside of the U-shaped pipe, and the velocity in the area is determined to be an effective impact velocity based on the extracted flow field velocity direction combined with the spatial position area, that is, the velocity pointing to the normal direction of the pipe wall without considering the viscous force of the fluid; 3.2 The effective impact velocity is calculated using the fluid dynamic pressure formula, including the calculation of the single-phase flow pressure inside the tube and the calculation of the multiphase flow pressure outside the tube, specifically: Where: α l is the liquid phase cavitation rate, ρ l is the liquid density, U l is the liquid superficial velocity, α v is the vapor phase cavitation rate, ρ v is the vapor phase density, U v is the superficial velocity of the vapor phase; 3.3 For the ineffective impact velocity, the viscosity force deviating from the pipeline and the viscosity force parallel to the pipeline are calculated by the fluid viscosity formula, including: single-phase flow in the pipeline and multiphase flow outside the pipeline, specifically: the viscosity force deviating from the pipeline Viscous force parallel to the pipe Where: μ is the multiphase flow viscosity, v n is the normal velocity, v t is the tangential velocity, fluid viscosity μ=α l μ l +α g μ g , μ l is the liquid viscosity, μ v is the vapor phase viscosity.

2. The method for reconstructing flow field force of flow-induced vibration of heat transfer tube of steam generator according to claim 1, characterized in that: The extraction of the near-wall area in the three-dimensional flow field data refers to: dividing the flow field simulation data to be processed, that is, the flow field unit area coordinates, density, cavitation rate, temperature, velocity, and pressure data into straight pipe sections and curved pipe sections, the inside and outside of the pipe according to the region; after discretizing the data after the division of the regions, the flow field unit area coordinates are converted into a polar coordinate system, and the near-wall area of ​​the heat transfer tube is extracted.

3. The method for reconstructing flow field force of flow-induced vibration of heat transfer tube of steam generator according to claim 1 or 2, characterized in that: The heat transfer tube near wall area refers to: the area within 0.15mm in the axial direction of the inner and outer tubes of the heat transfer tube.

4. The method for reconstructing flow field force of flow-induced vibration of heat transfer tube of steam generator according to claim 1, characterized in that: The radial synthesis and circumferential synthesis refer to: first synthesizing the flow field exciting forces generated in various circumferential regions of the heat transfer tube, ignoring the torque effect on the tube; and then synthesizing the exciting forces on the primary and secondary sides of the tube.

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