Design method for temperature distribution of concrete cave wall under short-time alternating temperature field

Abstract

The invention discloses a design method for temperature distribution of a concrete tunnel wall under a short-time alternating temperature field, provides a scientific and reasonable method for quantitatively determining a temperature action value of a main body structure aiming at an airflow alternating temperature action when a super-huge wind tunnel structure works, and provides structural design measures to ensure safety and reliability. The method is realized through the steps of determining and calculating wind tunnel parameters, establishing a three-dimensional model and processing parts, segmenting and encrypting grids, simplifying a heat exchanger and establishing a fluid-solid coupling model, setting boundary conditions, calculating, solving and screening the most unfavorable working condition and the like. According to the method, temperature distribution can be accurately determined, a model conforming to reality is established, complex boundary conditions are considered, the most unfavorable working conditions are screened for guiding design, the special requirements of wind tunnel structure design are met, and safety and reliability in a complex temperature environment are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of wind tunnel construction, and in particular to a design method for temperature distribution of a concrete tunnel wall under a short-time alternating temperature field. Background Art

[0002] As a complex multidisciplinary comprehensive project, a large-scale aeroacoustic wind tunnel integrates knowledge and technology from multiple disciplines such as aerodynamics, thermodynamics, materials science, structural mechanics, and measurement and control theory. During the actual operation of the wind tunnel, the heat dissipation effect of the fan will cause the air temperature in the flow channel to rise rapidly in a short period of time. This rapid temperature change will further trigger a series of complex temperature response phenomena in the main structure.

[0003] In the traditional scope of building structure design, the consideration of temperature effects is mainly focused on the impact of climate and environmental changes. Existing relevant load specifications, such as the "Building Structure Load Specification" GB50009-2012 and the "General Specification for Engineering Structures" GB5501-2021, only provide corresponding value references and calculation methods for temperature effects caused by common climate factors such as temperature changes and solar radiation. However, there is no special, in-depth research and targeted specification provisions for the temperature effects of airflow alternation generated by special structures such as super-large wind tunnels during their operation.

[0004] Traditional structural design methods have many limitations, which are particularly prominent when faced with the special temperature distribution of wind tunnel structures.

[0005] First, from the perspective of temperature value, the traditional method has the problem of not being comprehensive enough. In the general design process, for the same component at the same position, only a single temperature value can be used. Taking the large-scale wind tunnel as an example, its temperature distribution has unique characteristics. In the spatial dimension, the temperature difference of the tunnel wall in different areas is relatively small; however, when focusing on the same spatial position, the temperature difference in the small scale along the thickness direction of the tunnel wall is extremely significant. This complex temperature distribution is difficult for traditional design methods to accurately grasp and consider. Summary of the invention

[0006] The purpose of the present invention is to provide a design method for the temperature distribution of the concrete tunnel wall under a short-time alternating temperature field. The method can systematically provide a scientific and reasonable method for quantitatively determining the value of the temperature effect of the main structure for the specific scenario of the airflow alternating temperature effect generated by the super-large wind tunnel structure during operation, thereby ensuring the accuracy and rationality of the input conditions for the subsequent civil structure design.

[0007] The present invention is achieved through the following technical solutions:

[0008] A design method for temperature distribution of concrete cave wall under short-time alternating temperature field comprises the following steps:

[0009] S1. Identify and calculate relevant parameters of wind tunnel operation;

[0010] S2. Establish a three-dimensional model based on the wind tunnel shape parameters and process the guide vanes at the corners;

[0011] S3. Divide the model by structured grid method, establish a hexagonal structured grid model, and encrypt the grid near the wall and boundary layer;

[0012] S4. Abstract and simplify the heat exchanger inside the cave, import the mesh model into the calculation software, and determine the mesh accuracy of different areas and boundaries;

[0013] S5. Set the calculation boundary conditions according to the wind tunnel operation parameters, couple the wind tunnel inlet and outlet parameters, and set the initialization temperature, pressure and non-steady-state operation time parameters;

[0014] S6. Call the calculation software to calculate the turbulence and heat transfer process, solve the velocity temperature distribution, derive the temperature change law of the wall surface in the target area over time, and select the most unfavorable working condition based on the obtained data results.

[0015] In this proposal, the design method includes the steps of clarifying and calculating wind tunnel operation-related parameters, establishing a three-dimensional model and processing related components, dividing the model and encrypting the grid, simplifying the internal heat exchanger and establishing a fluid-solid coupling analysis model, setting complex boundary conditions, and calculating and solving and screening the most unfavorable working conditions. For wind tunnel structure design, it can accurately determine the temperature distribution, establish an analysis model that conforms to reality and consider complex boundary conditions. It can screen the most unfavorable working conditions to guide structural design measures and ensure the safety and reliability of the wind tunnel structure under the action of temperature.

[0016] As a further improvement scheme of the design method, in step S1, the parameters include the temperature or heat flux density of each outer wall under operating conditions, thermal parameters of the corresponding wall materials, each cold and heat source in the wind tunnel, and the law of change of fluid flow rate under each operating condition of the wind tunnel.

[0017] In this scheme, the temperature or heat flux density of each outer wall determines the initial and boundary conditions of the cave wall temperature. The thermal parameters of the wall material affect the heat transfer process and are also the basis for simulating the heat exchange process. The cold and heat sources affect the temperature field. The law of fluid flow rate changes affects the dynamic characteristics of heat exchange, providing input conditions for the entire design method, which is used to establish an accurate calculation model and realize accurate temperature calculation, so as to provide a basis for structural design by screening the most unfavorable working conditions.

[0018] As a further improvement of the design method, in step S2, the material type, geometric profile and scale, and equivalent thickness of the wind tunnel wall need to be extracted during the three-dimensional model building process.

[0019] In this scheme, the determination of material type helps to distinguish the characteristics of different materials (such as concrete and steel) in terms of heat transfer, mechanical properties, etc., providing a basis for the subsequent accurate simulation of temperature field and structural force analysis. At the same time, the clarification of geometric contours and scales can construct a three-dimensional model that conforms to the actual shape of the wind tunnel, making the model closer to the actual situation, thereby improving the accuracy and reliability of the simulation results; the extraction of equivalent thickness takes into account the complex situations that may exist in the actual structure (such as concrete beam-slab system), and converts structures such as beams and slabs into an average equivalent thickness, which simplifies the model while retaining the key characteristics of the structure to a certain extent, providing reasonable basic conditions for subsequent meshing and computational analysis.

[0020] As a further improvement plan for the design method, in step S2, when establishing the three-dimensional model, the overall framework and basic dimensions must first be determined based on the length, width, height, and shape and size information of each part of the wind tunnel. Then, the guide vanes in the corner section are modeled in the form of adiabatic walls in the model according to actual dimensions and meshed.

[0021] In this scheme, when establishing a three-dimensional model, the overall framework and basic dimensions are first determined based on the length, width, height, and shape and size information of each part of the wind tunnel. This provides a basic framework for building a model that conforms to the actual structure of the wind tunnel, ensuring that the model is consistent with the actual wind tunnel at a macro level, laying the foundation for subsequent precise modeling and analysis. The guide vanes in the corner section are then modeled in the model in the form of an adiabatic wall according to the actual size and meshed. This can accurately simulate the actual position and shape of the guide vanes in the wind tunnel, as well as their guiding effect on the airflow. Accurate modeling of the guide vanes is crucial for studying the flow characteristics of the airflow in the wind tunnel, and meshing provides a suitable mesh structure for subsequent numerical calculations, ensuring the accuracy and efficiency of the calculations, so that the entire model can more realistically reflect the actual working conditions of the wind tunnel.

[0022] As a further improvement of the design method, the grid size does not exceed 1 / 6 of the thickness of the cave wall.

[0023] In this scheme, a fine grid can more accurately capture the temperature gradient and heat flow changes near the tunnel wall, thereby improving the accuracy of the calculation of the temperature distribution of the concrete tunnel wall; if the grid scale is too large, it may lead to inaccurate simulation of the temperature field and heat flow, and fail to accurately reflect the actual physical phenomena near the tunnel wall, thereby affecting the entire design method's analysis of temperature distribution and the screening of the most unfavorable working conditions, and failing to provide reliable temperature data basis for wind tunnel structure design.

[0024] As a further improvement of the design method, in step S3, when the grids near the wall and the boundary layer are encrypted, no less than 6 grids are divided along the thickness direction of the concrete wall and the size of a single grid is in the range of 30 mm to 80 mm.

[0025] In this scheme, when the mesh near the wall and boundary layer is encrypted, the mesh setting of dividing no less than 6 meshes along the thickness direction of the concrete wall and the size of a single mesh in the range of 30mm to 80mm can more finely capture the temperature field and heat flow change information near the concrete wall. A sufficient number of meshes can more accurately describe the distribution gradient of temperature in the thickness direction of the wall, avoiding the temperature simulation distortion caused by too few meshes. At the same time, limiting the size of a single mesh within a reasonable range not only ensures sufficient resolution of physical phenomena near the wall, but also avoids the problem of excessive calculation caused by too fine a mesh, thereby improving the calculation accuracy while taking into account the calculation efficiency, providing a reliable mesh foundation for accurately analyzing the temperature distribution of the concrete cave wall and subsequently screening the most unfavorable working conditions.

[0026] As a further improvement of the design method, in step S4, when abstractly simplifying the heat exchanger inside the tunnel, the heat exchanger inside the wind tunnel is represented by an internal cold source, which is evenly distributed in the heat exchanger section.

[0027] In this scheme, the simplified method of representing the internal heat exchanger of the wind tunnel in the form of an internal cold source and evenly distributing it in the heat exchanger section effectively reduces the complexity of the model while retaining the key influence of the heat exchanger on the temperature field. By treating it as an internal cold source, the process of heat exchanger absorbing heat can be simulated, thereby reasonably reflecting its role in the temperature field. The setting of evenly distributing it in the heat exchanger section makes the simulation of the heat exchange effect of the heat exchanger more in line with the average level of actual conditions, which helps to more accurately analyze the distribution of the temperature field in subsequent calculations, and provides a more reasonable temperature field simulation basis for determining the temperature distribution of the concrete cave wall and the entire wind tunnel structure design. At the same time, it also reduces the problems of computing resource consumption and increased modeling difficulty caused by detailed modeling of the heat exchanger.

[0028] As a further improvement plan for the design method, in step S4, after the grid model is imported into the calculation software, the grid type is divided according to the area in the wind tunnel, the outer wall, inner wall, fluid inlet, fluid outlet, cold source area, heat source area and different wall material areas are determined, the boundary grid accuracy of the concrete wall area is retained, and the steel wall area is simplified to a grid boundary.

[0029] In this scheme, the outer wall, inner wall, fluid inlet, fluid outlet, cold source area, heat source area and different wall material areas are clearly distinguished, which can simulate and analyze the physical characteristics and boundary conditions of different areas more accurately. The boundary mesh accuracy of the concrete wall area is retained because concrete usually plays an important supporting and heat insulating role in the wind tunnel structure. A finer mesh helps to accurately capture the temperature changes and heat transfer process near the concrete wall, providing more reliable temperature data for structural design. The steel wall area is simplified to a mesh boundary. Considering that steel has good thermal conductivity and has a relatively small impact on the overall results in some cases, such simplification can reduce the amount of calculation without affecting the accuracy of key results. Through this targeted mesh processing method, the calculation efficiency can be improved while ensuring the accuracy of the calculation, laying the foundation for accurately analyzing the temperature field distribution and airflow inside the wind tunnel, thereby providing a scientific basis for the design of wind tunnel structures.

[0030] As a further improvement of the design method, in step S5, the k-epsilon turbulence equation is used to calculate the turbulence in the wind tunnel when the calculation software is called to calculate the turbulence and heat transfer process. At the same time, the energy equation is solved, the heat transfer process is calculated, and the model velocity and temperature distribution at the corresponding running time is solved.

[0031] In this scheme, the k-epsilon turbulence equation can be used to more accurately simulate the complex turbulent flow conditions in the wind tunnel. Turbulence has a significant impact on heat transfer and temperature distribution. Through accurate calculation of turbulence, we can better understand the motion characteristics of airflow in the wind tunnel and the heat transfer mechanism; solving the energy equation for heat transfer process calculation can clarify the heat transfer and distribution law in the wind tunnel, which is crucial for determining the temperature distribution of the concrete tunnel wall; solving the velocity temperature distribution of the model at the corresponding operating time can fully understand the fluid flow velocity and temperature changes of the wind tunnel in different operating stages, and provide detailed temperature and velocity data for structural design, so as to screen out the most unfavorable working conditions, thereby providing a scientific basis for the safety and reliability design of the wind tunnel structure.

[0032] As a further improvement plan for the design method, in step S5, after exporting the obtained data results, the most unfavorable working condition is selected according to the spatial distribution characteristics of the temperature in the concrete body in the obtained results and the time distribution characteristics as the wind tunnel runs, wherein the most unfavorable working condition is the condition with the highest average temperature rise of the tunnel wall and the condition with the largest gradient temperature difference.

[0033] In this scheme, by analyzing the spatial distribution characteristics of the temperature in the concrete body, the temperature difference of the concrete at different positions in the wind tunnel can be determined, and areas with higher temperatures or larger temperature changes can be found. These areas may be more susceptible to temperature stress and pose a potential threat to the safety of the wind tunnel structure. At the same time, considering the time distribution characteristics of the temperature as the wind tunnel runs, it is possible to understand the changing trend of the concrete temperature at different operation stages and determine the time period with the fastest temperature rise or continuous high temperature. Selecting the working conditions with the highest average temperature rise of the tunnel wall and the largest gradient temperature difference as the most unfavorable working conditions can provide a key reference for the design of the wind tunnel structure. Under the most unfavorable working conditions, the problems of temperature stress and thermal deformation faced by the wind tunnel structure are the most prominent. Focus analysis and design optimization can be carried out for these working conditions, and corresponding structural design measures can be taken, such as strengthening reinforcement and using high temperature resistant materials, to ensure that the wind tunnel can maintain the safety and stability of the structure under various operating conditions.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] 1. Through precise modeling and calculation, the present invention can accurately determine the temperature distribution of the concrete wall during the operation of the wind tunnel, including the temperature variation over time and space, which provides a scientific basis for the design of the wind tunnel structure and allows for reasonable structural design based on the temperature distribution results;

[0036] 2. The present invention can evaluate and optimize the performance of the wind tunnel under extreme conditions by screening the most unfavorable working conditions, thereby improving the safety and reliability of wind tunnel operation;

[0037] 3. The present invention can discover potential problems in advance during the design stage through accurate temperature distribution analysis, avoiding structural damage caused by temperature factors during construction and operation, thereby reducing design costs and risks. At the same time, efficient calculation methods and reasonable model simplification can also reduce calculation time and resource consumption during the design process, helping to improve design efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0039] Figure 1 It is a schematic diagram of heat transfer between airflow and wind tunnel in the prior art;

[0040] Figure 2 It is a design flow chart of the present invention;

[0041] Figure 3 is a schematic diagram of a wind tunnel model of the present invention;

[0042] Figure 4 for Figure 3 An enlarged structural diagram of the middle corner section;

[0043] Figure 5 is a schematic diagram of a wind tunnel grid of the present invention;

[0044] Figure 6 Schematic diagram of the distribution of physical parameters in different areas of the wind tunnel;

[0045] Figure 7 This is the temperature distribution diagram along the rear side of the cave wall at 600 seconds in working condition 2;

[0046] Figure 8 This is a schematic diagram of the air temperature distribution in the tunnel at 600 seconds under working condition 2;

[0047] Fig. 9 This is the air flow temperature diagram of working condition 2;

[0048] Fig.10 It is the top plate temperature diagram of working condition 2;

[0049] Fig.11 is the side wall temperature diagram of working condition 2;

[0050] Fig.12 This is the air flow temperature diagram of working condition 4;

[0051] Fig.13 It is the top plate temperature diagram of working condition 4;

[0052] Fig.14 is the side wall temperature diagram of working condition 4;

[0053] Fig.15 This is the air flow temperature diagram of the wind tunnel during natural cooling.

[0054] Marks and corresponding parts names in the attached drawings:

[0055] 1-corner section, 2-heat exchanger section, 3-fluid inlet, 4-fluid outlet, 5-copper wall area, 6-guide vane, 7-fourth diffusion section. DETAILED DESCRIPTION

[0056] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0057] like Figure 1The figure shows the flow of air in the wind tunnel and its heat transfer with the wind tunnel. During the operation of the wind tunnel, the internal temperature field changes with a large amplitude (up to 60°C, far exceeding the ambient temperature) and a short change time (the temperature can be raised within 10 minutes to 1 hour). As a result, the temperature change of the main structure is significantly different from the ambient temperature. The determination of the short-term alternating temperature field is the basis of civil engineering structure design. There is no relevant research data and specifications on how to quantitatively determine the temperature distribution in the concrete structure under this temperature field. Therefore, the following embodiments are proposed:

[0058] This embodiment provides a design method for the temperature distribution of the concrete cave wall under a short-term alternating temperature field. Figure 2-Figure 7 As shown, the following steps are included:

[0059] S1. Define and calculate the relevant parameters of wind tunnel operation. The parameters include the temperature or heat flux density of each outer wall under operation conditions, the thermal parameters of the corresponding wall materials, the cold and hot sources in the wind tunnel (including fans, cooling coils, etc.) and the change law of fluid flow rate under each wind tunnel operation condition; specifically, it includes determining the measurement position, selecting the measuring instrument, formulating the measurement time plan, and then measuring the temperature or heat flux density of each outer wall under operation conditions. The temperature can be measured directly. If the heat flux density needs to be calculated, the relevant equation is used to combine the thermal parameters of the wall materials and the ambient temperature. Then the thermal parameters of the corresponding wall materials are determined. The data can be consulted or experimentally determined when necessary. Then the cold and hot sources in the wind tunnel are determined, the cold sources and heat sources are identified, and their related characteristics and heat generation are understood. Finally, the change law of fluid flow rate under each wind tunnel operation condition is determined, and the change law is fitted with a suitable function by measuring the flow rate data and analyzing and modeling.

[0060] After the wind tunnel operation related parameters are collected, the process goes to step S2. A three-dimensional model is established according to the wind tunnel shape parameters, and the guide vanes at the corner sections are processed;

[0061] In this step, a three-dimensional model is established based on the wind tunnel shape parameters to ensure the wall thickness parameters and the shape accuracy of the internal resistance parts. The guide vanes (6) in the corner section (1) need to be realistically reflected, and are modeled in the form of an adiabatic wall at the relevant position of the model according to the actual size and meshed. Specifically, the model is modeled according to the actual construction drawing size, and the type of material used for the tunnel wall (distinguishing between steel and concrete), the geometric contour and geometric scale of the tunnel wall, and the equivalent thickness of the tunnel wall material (such as a concrete beam-slab system, the distribution of structural beams and slabs is not important, and the beams and slabs are converted together to an average equivalent slab thickness) are extracted. The above-mentioned extracted factors are restored to the actual concrete wall thickness and internal geometric shape through the model. The accuracy of the gas velocity field in the wind tunnel is improved by geometric shape restoration, and the accuracy of the temperature field in the simulation is increased by the actual wall thickness. The three-dimensional model of the model is established based on the drawing data, such as Figure 3 and Figure 4As shown in FIG. 1 , the established wind tunnel model includes the heat exchanger section 2, the corner section 1, the copper wall area 5 and the guide vane 6, and as shown in FIG. Figure 6 As shown, the external steel structure and the concrete mechanism area are distinguished, and the fan section is simulated and calculated through inlet and outlet programming. Therefore, in the three-dimensional model, only the inlet and outlet sections, namely, the fluid inlet 3 and the fluid outlet 4, are retained for the fan section.

[0062] The model is meshed in step S3 while ensuring the calculation accuracy, the model is divided by structured meshing, a hexagonal structured mesh model is established, and the mesh near the wall and boundary layer is encrypted;

[0063] Specifically, import the 3D wind tunnel model into the meshing tool, ensure that the geometry and size of the model do not change during the import process, and that all parts and boundaries can be correctly identified; according to the geometry of the wind tunnel, use the cutting function in the meshing tool to cut the model along the appropriate direction. For example, for a circular wind tunnel, you can cut along the circumferential and axial directions; for a rectangular wind tunnel, you can cut along the length, width, and height directions. The purpose of cutting is to decompose a complex model into multiple simple sub-areas to facilitate the establishment of a structured grid.

[0064] In the cut sub-area, use the meshing tool to create a hexagonal structured grid. The grid size cannot exceed 1 / 6 of the hole wall thickness. Among them, no less than 6 grids need to be divided along the thickness of the concrete wall. The size of a single grid is in the range of 30 to 80 mm. Since the hexagonal grid has good geometric characteristics, it can reduce the distortion and deformation of the grid and improve the grid quality while ensuring a certain grid density. Then, according to the shape and size of the sub-area, set the side length, angle and other parameters of the hexagonal grid to ensure that the grid can evenly fill the sub-area, and then identify the grid area near the wall and boundary layer. In the meshing tool, you can identify the grid near the wall and boundary layer by setting boundary conditions or selecting specific geometric areas, and use appropriate encryption methods to encrypt the grid near the wall and boundary layer. The meshing is as follows: Figure 5 In this embodiment, common encryption methods include local grid refinement or multi-layer grid or adaptive grid.

[0065] S4. Abstract and simplify the heat exchanger inside the cave, import the mesh model into the calculation software, and determine the mesh accuracy of different areas and boundaries;

[0066] Specifically, the principles and methods of simplification are first determined based on the actual role of the heat exchanger in the wind tunnel and the main ways in which it affects the temperature field. For example, the heat exchanger inside the wind tunnel can be represented by an internal cold source, which is evenly distributed in the heat exchanger section 2, and its detailed internal structure and complex fluid flow process are ignored. Then, according to the actual cooling power, position, size and other information of the heat exchanger, the corresponding parameters are set in the simplified model. For example, the temperature of the internal cold source, the heat exchange coefficient and other parameters are determined to simulate the cooling effect of the heat exchanger on the surrounding environment.

[0067] Then, the mesh model including the overall structure of the wind tunnel and the encrypted mesh model generated in the previous step S3 is imported into the ANSYS or C wind tunnel calculation software, and the mesh type is divided according to the area in the wind tunnel, and the outer wall, inner wall, fluid inlet, fluid outlet, cold source area, heat source area and different wall material areas are determined, and the boundary mesh accuracy of the concrete wall area is retained, and the steel wall area (5) is simplified to a mesh boundary. More specifically, during the import process, the calculation software identifies different areas of the wind tunnel model, such as the outer wall, inner wall, fluid inlet, fluid outlet, cold source area, heat source area and different wall material areas, and determines the mesh accuracy of each area according to the importance of different areas and the degree of influence on the calculation results. For example, for the wall area, especially the area close to the temperature change (such as close to the cold source or heat source), a high mesh accuracy should be maintained to accurately capture the temperature change gradient; for the fluid area, the appropriate mesh accuracy can be set according to the flow characteristics of the fluid and the limitation of the calculation resources; for the boundary mesh, its accuracy is also determined according to the nature of the boundary and the degree of influence on the calculation results. For example, for fluid-solid interfaces, high accuracy should be maintained to ensure that heat transfer and mechanical interactions between the fluid and solid are simulated correctly.

[0068] S5. Set the calculation boundary conditions according to the wind tunnel operation parameters, couple the wind tunnel inlet and outlet parameters, and set the initialization temperature, pressure and non-steady-state operation time parameters;

[0069] Specifically, first, according to the wind tunnel operation parameters obtained in the above steps, including fan power, flow rate, temperature and pressure at different positions, the flow characteristics and related parameter ranges and change laws at the fluid inlet 3 and fluid outlet 4 are clarified. Then, the wind tunnel inlet boundary conditions are set, the average inlet velocity is calculated by fan power and flow rate, and the distribution mode is set considering the velocity non-uniformity. At the same time, the fluid inlet 3 temperature and pressure are determined according to actual measurement values ​​or experience. For unsteady operation, its change law over time should also be considered and the corresponding function is set. Then, the wind tunnel outlet boundary conditions are set, and the outlet pressure is determined considering the external environmental pressure and internal resistance. If other equipment is connected, it is determined as required, and the parameters at the fluid inlet 3 and fluid outlet 4 are coupled according to the law of conservation of mass and energy. Finally, the initialization temperature, pressure and unsteady operation time parameters are set, and the initial value is set in the entire model according to the actual situation of wind tunnel startup. The corresponding function is set considering the change law of temperature and pressure in different regions over time during unsteady operation. At the same time, the total time and time step of unsteady operation are determined according to the actual operation time requirements and research purposes, and the appropriate time step is determined by trial calculation or reference experience.

[0070] In this embodiment, the design of wind tunnel boundary conditions, for the outer surface: the third type of boundary conditions are considered, and the outer surface convection heat transfer coefficient and the outdoor air flow temperature are input during simulation to calculate the heat transfer between the outer surface and the air. The outer surface convection heat transfer coefficient is taken as: h = 18.7; for the inner surface, fluid-solid coupling heat transfer, the calculation software calculates it automatically, and the following conditions are set for different working conditions:

[0071] (1) Working condition 1:

[0072] Fan input power: 280MW Outdoor temperature and initial temperature in wind tunnel: 30℃

[0073] Running time: 10min Mass flow rate: 53112.7kg / s

[0074] Control requirements: air flow temperature is not higher than 60℃

[0075] Cooling power of cooling section: Q = -t air 2 *116.72+10855*t air -41417

[0076] Where:

[0077] ——Average temperature of gas in the wind tunnel, °C, when the cooler is started;

[0078] Q——Cooling power of cooler, W / m 3 ;

[0079] (2) Working condition 2:

[0080] Fan input power: 280MW Outdoor temperature and initial temperature in wind tunnel: -3℃

[0081] Running time: 10min Mass flow rate: 53112.7kg / s

[0082] Control requirements: air flow temperature is not higher than 60℃

[0083] Cooling power of cooling section: Q = -t air 2 *116.72+10855*t air -41417

[0084] Where:

[0085] ——Average temperature of gas in the wind tunnel, °C, when the cooler is started;

[0086] Q——Cooling power of cooler, W / m 3 ;

[0087] S6. Call the calculation software to calculate the turbulence and heat transfer process, solve the velocity temperature distribution, derive the temperature change law of the wall surface in the target area over time, and select the most unfavorable working condition based on the obtained data results.

[0088] Specifically, PHOENICS software is called for simulation calculation, the above-mentioned operating parameters are set in the PHOENICS software, and the calculation software is called to calculate the turbulence and heat transfer process. The k-epsilon turbulence equation is used to calculate the turbulence in the wind tunnel, and the energy equation is solved at the same time. The heat transfer process is calculated and the velocity temperature distribution of the model under the corresponding running time is solved. After the calculation is completed, the calculation results of the velocity temperature distribution are obtained, and the target area is determined according to the research purpose and needs. In this embodiment, the fourth diffuser 7 is taken as a typical position for analysis.

[0089] In this embodiment, the calculation results for working condition 1 are as follows: Figure 7-Figure 9 As shown, operating condition 1 meets the control condition that the temperature does not exceed 60°C for 10 minutes of operation; Figure 10-11 As shown, for working condition 1, the internal temperature is higher and the wall temperature is lower, and the influence of the internal temperature on avoiding the internal temperature field is affected by the distance.

[0090] For the calculation results of working condition 2: Fig.12 It can be seen that the second working condition meets the requirement that the operating temperature does not exceed 60℃. Figure 13-14 It can be seen that the temperature distribution law remains basically unchanged under the operating condition 2.

[0091] At the same time, in this embodiment, in order to analyze the natural cooling of the gas in the wind tunnel, under the working condition 1, the system stops running the fan and closes the cooling section after running for 20 minutes. The temperature change of the air flow in the wind tunnel is as follows: Fig.15 As shown in the figure, due to the thick walls and large scale of the wind tunnel, the wind tunnel has a certain thermal inertia and a slow natural cooling rate. After stopping working for about 1000 minutes, the temperature is still above 40°C, which is much higher than the initial temperature of the wind tunnel of 30°C.

[0092] The above-obtained data results are derived. According to the spatial distribution characteristics of the temperature in the concrete body and the time distribution characteristics of the wind tunnel operation, the most unfavorable working condition is selected. Among them, the most unfavorable working condition is the condition with the highest average temperature rise of the tunnel wall and the condition with the largest gradient temperature difference. The following optimization design conclusions of the wind tunnel structure are obtained:

[0093] 1) In the 70MW heat rejection power condition, due to the small amount of heat rejection and the relatively large amount of heat absorbed by the heat exchanger, the overall air flow temperature is not high. Due to the existence of the heat exchanger, the heat rejection is basically absorbed by the heat exchanger. The air flow temperature rises within 5 degrees during the entire operation process. At this time, the temperature inside the cave enclosure structure is low, and the temperature difference between the inner and outer surfaces of the cave wall is about 2 degrees, which fully meets the requirement that the air temperature rise is not higher than 50 degrees after 10 minutes of operation.

[0094] 2) In the 280MW heat rejection power condition, it is greatly affected by the initial temperature. When the initial temperature is 30 degrees, due to the functional relationship between the heat absorption of the heat exchanger and the air temperature, the heat absorption of the heat exchanger is relatively large. During the entire operation process, 73% of the heat rejection is absorbed by the heat exchanger, 1% of the heat is dissipated to the outside through the enclosure structure of the steel structure, and 17% of the heat is absorbed by the air, resulting in an increase in the wind tunnel air temperature. When the operation time is 10 minutes, the overall average temperature of the airflow is 50 degrees, which meets the experimental working condition requirements. During the operation of this condition, the enclosure structure absorbs a large amount of heat, resulting in a large temperature gradient inside it. The temperature difference between the inner and outer surfaces of the tunnel reaches 30 degrees. The thermal stress caused by the temperature gradient needs to be considered in the structural design.

[0095] 3) In the 280MW heat rejection power condition, when the initial temperature is -3 degrees, due to the functional relationship between the heat absorption of the heat exchanger and the air temperature, the heat absorption of the heat exchanger is relatively small. During the entire operation process, only 58% of the heat is absorbed by the heat exchanger, 2% of the heat is dissipated to the outside through the enclosure structure of the steel structure, and 23% of the heat is absorbed by the air, resulting in an increase in the wind tunnel air temperature. When the operation time is 10 minutes, the overall average temperature of the airflow is 38 degrees, which meets the experimental working condition requirements. During the operation of this condition, the heat absorption of the enclosure structure increases, resulting in a large temperature gradient inside it. The temperature difference between the inner and outer surfaces of the tunnel reaches 40 degrees, which is the condition with the largest gradient temperature difference. The thermal stress caused by the temperature gradient needs to be considered in the structural design.

[0096] 4) Analysis of the calculation results of high-power and long-term working conditions shows that if the wind tunnel is not cooled by the cooling section after operation, the effect of natural cooling on the cooling of the wind tunnel will decrease over time and the high temperature in the wind tunnel may be maintained for a long time.

[0097] In summary, through the heat transfer and flow coupling calculation of the present invention, the detailed temporal and spatial distribution laws of the cave temperature and heat changes under different working conditions are obtained, which can provide input conditions for the subsequent analysis of temperature and thermal stress.

[0098] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A design method for temperature distribution of concrete cave wall under short-time alternating temperature field, characterized in that: The steps include: S1. Identify and calculate relevant parameters of wind tunnel operation; S2. Establish a three-dimensional model based on the wind tunnel shape parameters and process the guide vanes at the corners; S3. Divide the model by structured grid method, establish a hexagonal structured grid model, and encrypt the grid near the wall and boundary layer; S4. Abstract and simplify the heat exchanger inside the cave, import the mesh model into the calculation software, and determine the mesh accuracy of different areas and boundaries; S5. Set the calculation boundary conditions according to the wind tunnel operation parameters, couple the wind tunnel inlet and outlet parameters, and set the initialization temperature, pressure and non-steady-state operation time parameters; S6. Call the calculation software to calculate the turbulence and heat transfer process, solve the velocity temperature distribution, derive the temperature change law of the wall surface in the target area over time, and select the most unfavorable working condition based on the obtained data results.

2. The design method of temperature distribution of concrete cave wall under short-time alternating temperature field according to claim 1 is characterized in that: In step S1, the parameters include the temperature or heat flux density of each outer wall under operation conditions, thermal parameters of the corresponding wall materials, each cold and heat source in the wind tunnel, and the change law of the fluid flow rate under each operation condition of the wind tunnel.

3. The design method of temperature distribution of concrete cave wall under short-time alternating temperature field according to claim 1 is characterized in that: In step S2, the material type, geometric profile and scale, and equivalent thickness of the wind tunnel wall need to be extracted during the three-dimensional model building process.

4. The design method of temperature distribution of concrete cave wall under short-time alternating temperature field according to claim 3 is characterized in that: In step S2, when establishing a three-dimensional model, the overall framework and basic dimensions must first be determined based on the length, width, height, and shape and size information of each part of the wind tunnel. Then, the guide vanes (6) in the corner section (1) are modeled in the model in the form of an adiabatic wall according to the actual dimensions and meshed.

5. The design method of temperature distribution of concrete cave wall under short-time alternating temperature field according to claim 4 is characterized in that: The grid size does not exceed 1 / 6 of the thickness of the cave wall.

6. The design method of temperature distribution of concrete cave wall under short-time alternating temperature field according to claim 1 is characterized in that: In step S3, when the grids near the wall surface and the boundary layer are encrypted, no less than 6 grids are divided along the thickness direction of the concrete wall and the size of a single grid is in the range of 30 mm to 80 mm.

7. The design method of temperature distribution of concrete cave wall under short-time alternating temperature field according to claim 1 is characterized in that: In step S4, when abstracting and simplifying the heat exchanger inside the tunnel, the heat exchanger inside the wind tunnel is represented by an internal cold source, which is evenly distributed in the heat exchanger section (2).

8. The design method of temperature distribution of concrete cave wall under short-time alternating temperature field according to claim 7 is characterized in that: In step S4, after the grid model is imported into the calculation software, the grid type is divided according to the area in the wind tunnel, the outer wall, inner wall, fluid inlet, fluid outlet, cold source area, heat source area and the areas of different wall materials are determined, the boundary grid accuracy of the concrete wall area is retained, and the steel wall area (5) is simplified to a grid boundary.

9. The design method of temperature distribution of concrete cave wall under short-time alternating temperature field according to claim 1 is characterized in that: In step S5, the k-epsilon turbulence equation is used to calculate the turbulence in the wind tunnel when the calculation software is called to calculate the turbulence and heat transfer process, and the energy equation is solved at the same time to calculate the heat transfer process and solve the model velocity and temperature distribution at the corresponding running time.

10. The design method of temperature distribution of concrete cave wall under short-time alternating temperature field according to claim 9 is characterized in that: In step S5, after the obtained data results are exported, the most unfavorable working condition is selected according to the spatial distribution characteristics of the temperature in the concrete body in the obtained results and the temporal distribution characteristics as the wind tunnel runs, wherein the most unfavorable working condition is the condition with the highest average temperature rise of the tunnel wall and the condition with the largest gradient temperature difference.

Images