A design method for temperature distribution of concrete cavity wall under short-time alternating temperature field

Abstract

This invention discloses a method for designing the temperature distribution of concrete tunnel walls under short-term alternating temperature fields. This method provides a scientific and rational method for quantitatively determining the temperature effects of the main structure during the operation of an extra-large wind tunnel structure, and proposes structural design measures to ensure safety and reliability. This method is implemented by clarifying and calculating wind tunnel parameters, establishing a three-dimensional model and processing components, creating a dense grid, simplifying the heat exchanger to establish a fluid-solid coupling model, setting boundary conditions, and calculating and screening the most unfavorable operating conditions. This method accurately determines the temperature distribution, establishes a realistic model, considers complex boundary conditions, and screens the most unfavorable operating conditions to guide design, meeting the special requirements of wind tunnel structural design and ensuring safety and reliability in complex temperature environments.

Description

Technical Field

[0001] The present 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 project, a large-scale aeroacoustic wind tunnel integrates knowledge and technologies from a variety of disciplines, including aerodynamics, thermodynamics, materials science, structural mechanics, and measurement and control theory. During actual wind tunnel operation, the cooling effect of the fan causes the air temperature within the flow channel to rise rapidly within a short period of time. This rapid temperature change further triggers a series of complex temperature responses in the main structure.

[0003] In traditional building structure design, consideration of temperature effects primarily focuses on the impact of climate change. Existing load specifications, such as the "Code for Loads on Building Structures" GB50009-2012 and the "General Code for Engineering Structures" GB5501-2021, only provide reference values ​​and calculation methods for temperature effects caused by common climate factors such as temperature fluctuations and solar radiation. However, there is no dedicated, in-depth research or specific regulatory provisions for the temperature effects of alternating airflow generated during the operation of specialized structures such as extra-large wind tunnels.

[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 selection, traditional methods lack comprehensive considerations. In typical design processes, only a single temperature value is often used for the same component in the same location. Large-scale wind tunnels, for example, exhibit unique temperature distribution characteristics. Spatially, the temperature differences between different areas of the tunnel wall are relatively small; however, when focused on the same spatial location, the temperature differences within the small-scale range along the thickness of the tunnel wall are extremely significant. This complex temperature distribution is difficult for traditional design methods to accurately grasp and account for. Summary of the Invention

[0006] The purpose of the present invention is to provide a design method for the temperature distribution of concrete tunnel walls under a short-term alternating temperature field. This method can systematically target the specific scenario of the alternating temperature effect of airflow generated by an extra-large wind tunnel structure during operation, provide a scientific and reasonable method that can quantitatively determine the value of the temperature effect on the main structure, and ensure the accuracy and rationality of the input conditions for subsequent civil structure design.

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

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

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

[0010] S2. Build a 3D model based on the wind tunnel geometry parameters and process the corner guide vanes, etc.

[0011] S3. Divide the model into structured grids, establish a hexagonal structured grid model, and refine 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 initial temperature, pressure, and unsteady-state operation time parameters;

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

[0015] In this proposal, the design method includes 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 screening the most unfavorable working conditions. For wind tunnel structural design, it can accurately determine the temperature distribution, establish an analysis model that conforms to reality and consider complex boundary conditions. The most unfavorable working conditions can be screened to guide structural design measures, ensuring the safety and reliability of the wind tunnel structure under the action of temperature.

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

[0017] In this scheme, the temperature or heat flux density of each external 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 change law of the fluid flow rate affects the dynamic characteristics of the 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 screening the most unfavorable working conditions for structural design.

[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 subsequent accurate simulation of temperature fields and structural stress analysis. At the same time, the clear geometric outline and scale can construct a three-dimensional model that conforms to the actual shape of the wind tunnel, making the model closer to the real 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 beams, slabs and other structures into an average equivalent thickness, which simplifies the model while retaining the key characteristics of the structure to a certain extent, providing a reasonable basic condition for subsequent meshing and computational analysis.

[0020] As a further improvement to 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 sections are modeled in the form of adiabatic walls according to their 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 on a macro scale, and 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 adiabatic walls according to actual dimensions 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 temperature distribution calculation 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 grid near the wall and boundary layer is encrypted, no less than 6 grids are divided along the thickness direction of the concrete wall and the size of each grid is in the range of 30 mm to 80 mm.

[0025] In this solution, when meshing the wall and boundary layer, a grid configuration with no fewer than six grids along the thickness of the concrete wall and a single grid size ranging from 30mm to 80mm allows for more precise capture of temperature field and heat flux variations near the concrete wall. A sufficient number of grids can more accurately describe the temperature distribution gradient along the wall thickness, avoiding temperature simulation distortion caused by too few grids. Simultaneously, limiting the single grid size to a reasonable range ensures sufficient resolution of physical phenomena near the wall while avoiding the excessive computational effort associated with overly fine grids. This improves computational accuracy while maintaining efficiency, providing a reliable grid foundation for accurate analysis of concrete cavity wall temperature distribution and subsequent screening of the most unfavorable working conditions.

[0026] As a further improvement of the design method, 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.

[0027] In this solution, a simplified approach, representing the internal heat exchanger of the wind tunnel as an internal cold source and evenly distributing it throughout the heat exchanger section, effectively reduces the complexity of the model while retaining the heat exchanger's key influence on the temperature field. By treating it as an internal cold source, the process of heat absorption by the heat exchanger can be simulated, thereby reasonably reflecting its role in the temperature field. The setting of uniform distribution throughout the heat exchanger section makes the simulation of the heat exchange effect of the heat exchanger more consistent with the average level of actual conditions, which helps to more accurately analyze the distribution of the temperature field in subsequent calculations, providing a more reasonable temperature field simulation foundation for determining the temperature distribution of the concrete tunnel wall and the design of the entire wind tunnel structure. It also reduces the computational resource consumption and increased modeling difficulty that may be caused by detailed modeling of the heat exchanger.

[0028] As a further improvement of 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, and 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 solution, the outer wall, inner wall, fluid inlet, fluid outlet, cold source area, heat source area, and areas of different wall materials are clearly distinguished, enabling more accurate simulation and analysis of the physical properties and boundary conditions of different areas. The boundary mesh accuracy of the concrete wall area is retained because concrete usually plays an important supporting and thermal insulation 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 the good thermal conductivity of steel and its 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 accurate analysis of the temperature field distribution and airflow conditions inside the wind tunnel, thus providing a scientific basis for wind tunnel structure design.

[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 under 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 the airflow in the wind tunnel and the heat transfer mechanism; solving the energy equation to calculate the heat transfer process can clarify the heat transfer and distribution rules in the wind tunnel, which is crucial for determining the temperature distribution of the concrete tunnel wall; solving the velocity and temperature distribution of the model under the corresponding operating time can fully understand the fluid flow velocity and temperature changes of the wind tunnel in different operating stages, providing 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 scheme for the design method, in step S5, after the obtained data results are exported, the most unfavorable working condition is selected based on the spatial distribution characteristics of the temperature in the concrete body and the temporal distribution characteristics as the wind tunnel is running. The most unfavorable working condition is the working condition with the highest average temperature rise of the tunnel wall and the largest gradient temperature difference.

[0033] In this approach, by analyzing the spatial distribution characteristics of the temperature within the main concrete structure, it is possible to determine the temperature differences of the concrete at different locations in the wind tunnel and identify areas with higher temperatures or greater temperature variations. 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 temporal distribution characteristics of temperature as the wind tunnel operates, it is possible to understand the changing trends of concrete temperature during different operating stages and determine the time periods with the fastest temperature rise or sustained high temperatures. Selecting the conditions with the highest average temperature rise in the tunnel wall and the largest gradient temperature difference as the most unfavorable conditions can provide a key reference for wind tunnel structural design. Under the most unfavorable conditions, the problems of temperature stress and thermal deformation faced by the wind tunnel structure are most prominent. These conditions can be analyzed and optimized in detail, and corresponding structural design measures can be taken, such as strengthening reinforcement and using high-temperature resistant materials, to ensure that the wind tunnel maintains structural safety and stability 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, this invention can accurately determine the temperature distribution of the concrete wall during wind tunnel operation, including the temperature variation over time and space. This provides a scientific basis for wind tunnel structural design, and reasonable structural design can be carried out based on the temperature distribution results.

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

[0037] 3. Through accurate temperature distribution analysis, this invention can identify potential problems early in the design phase, preventing structural damage caused by temperature factors during construction and operation, thereby reducing design costs and risks. Furthermore, efficient calculation methods and reasonable model simplification can also reduce computing 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 This is a diagram of the heat transfer principle of airflow and wind tunnel in the prior art;

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

[0041] Figure 3 Schematic diagram of the 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 A schematic diagram of the 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 cavern 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] Figure 9 This is the air flow temperature diagram of working condition 2;

[0048] Figure 10 This is the top plate temperature diagram of working condition 2;

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

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

[0051] Figure 13 This is the top plate temperature diagram of working condition 4;

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

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

[0054] Markings and corresponding parts names in the accompanying 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 examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0057] like Figure 1The figure shows the airflow within the wind tunnel and its heat transfer. During wind tunnel operation, the internal temperature field exhibits large fluctuations (reaching up to 60°C, far exceeding the ambient temperature) and short durations (heating can be completed within 10 minutes to 1 hour). This impact on the temperature of the main structure is significantly different from the ambient temperature. Determining short-term alternating temperature fields is fundamental to civil engineering design. However, there is no relevant research data or regulatory requirements for quantitatively determining the temperature distribution within concrete structures under these temperature fields. Therefore, the following example is proposed:

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

[0059] S1. Identify and calculate the parameters related to 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 various 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 location, selecting the measuring instrument, formulating a 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 equations are used in combination with 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 measured when necessary. Then, the various 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. By measuring the flow rate data and analyzing and modeling, the change law is fitted with a suitable function.

[0060] After the wind tunnel operation parameters are collected, step S2 is entered. A three-dimensional model is established based on the wind tunnel shape parameters, and the corner guide vanes 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 blades (6) in the corner section (1) need to be realistically reflected and 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 outline and geometric scale of the tunnel wall, and the equivalent thickness of the tunnel wall material (such as the 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, the 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. The fan section is simulated and calculated through inlet and outlet programming. Therefore, only the inlet and outlet sections, namely the fluid inlet 3 and the fluid outlet 4, are retained in the fan section in the three-dimensional model.

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

[0063] Specifically, the 3D wind tunnel model is imported into the meshing tool, ensuring that the model's geometry and dimensions remain unchanged during the import process and that all components and boundaries are correctly identified. Based on the wind tunnel's geometry, the meshing tool's cutting function is used to cut the model in appropriate directions. For example, for a circular wind tunnel, cutting can be performed along the circumference and axial directions; for a rectangular wind tunnel, cutting can be performed along the length, width, and height directions. The purpose of cutting is to decompose the complex model into multiple simple sub-regions to facilitate the creation of a structured mesh.

[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 direction 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 a specific geometric area, and use a suitable encryption method to encrypt the grid near the wall and boundary layer. The meshing is as follows: Figure 5 In this embodiment, common refinement 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 its main impact on the temperature field. For example, the heat exchanger inside the wind tunnel can be represented by an internal cold source, evenly distributed in heat exchanger section 2, ignoring its detailed internal structure and complex fluid flow process. Then, based on information such as the actual cooling power, position, and size of the heat exchanger, corresponding parameters are set in the simplified model. For example, parameters such as the temperature of the internal cold source and the heat exchange coefficient are determined to simulate the cooling effect of the heat exchanger on the surrounding environment.

[0067] Then, the mesh model containing the whole structure of the wind tunnel and the encrypted mesh generated in step S3 is imported into ANSYS or C wind tunnel calculation software. 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 the areas of different wall materials are determined. The boundary mesh accuracy of the concrete wall area is retained, and the steel wall area (5) is simplified to the 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 areas of different wall materials, 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 near the area with large temperature changes (such as near the cold source or heat source), a high mesh accuracy should be maintained to accurately capture the temperature gradient; for the fluid area, the appropriate mesh accuracy can be set according to the flow characteristics of the fluid and the limitation of computing 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 initial temperature, pressure, and unsteady-state operation time parameters;

[0069] Specifically, first, based on the wind tunnel operating parameters obtained in the previous steps, including fan power, flow rate, temperature at different locations, and pressure, the flow characteristics at fluid inlet 3 and fluid outlet 4, as well as the ranges and variations of related parameters, are determined. Next, the wind tunnel inlet boundary conditions are set. The average inlet velocity is calculated using fan power and flow rate, and a distribution pattern is set to account for velocity nonuniformity. The temperature and pressure at fluid inlet 3 are determined based on actual measurements or experience. For unsteady operation, their temporal variations are also considered and corresponding functions are set. Next, the wind tunnel outlet boundary conditions are set, and the outlet pressure is determined by considering the external environmental pressure and internal resistance. If other equipment is connected, these pressures are determined as required. The parameters at fluid inlet 3 and fluid outlet 4 are coupled according to the laws of conservation of mass and energy. Finally, the initial temperature, pressure, and unsteady operation time parameters are set. Initial values ​​are set throughout the model based on the actual wind tunnel startup conditions. The corresponding functions are set to account for the temporal variations of temperature and pressure in different regions during unsteady operation. The total unsteady operation time and time step are determined based on the actual operation time requirements and research objectives. An appropriate time step is determined through trial calculations or empirical reference.

[0070] In this embodiment, the design of the wind tunnel boundary conditions is based on the third type of boundary conditions for the outer surface. During the simulation, the outer surface convection heat transfer coefficient and the outdoor air temperature are input to calculate the heat transfer between the outer surface and the air. The outer surface convection heat transfer coefficient is set to h = 18.7. For the inner surface, the fluid-solid coupled heat transfer is calculated by the calculation software. 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 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 the 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 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 the gas in the wind tunnel, °C, when the cooler is started;

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

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

[0088] Specifically, the PHOENICS software is called for simulation calculations. The above-mentioned operating parameters are set in the PHOENICS software. When 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. At the same time, the energy equation is solved, the heat transfer process is calculated, and the velocity and temperature distribution of the model under the corresponding running time is solved. After the calculation is completed, the calculation results of the velocity and temperature distribution are obtained. The target area is determined according to the research purpose and requirements. In this embodiment, the fourth diffuser 7 is used as a typical location 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℃ for 10 minutes; Figure 10-11 As shown in the figure, for working condition 1, the internal temperature is higher and the wall temperature is lower, and the influence of the internal temperature on the internal temperature field is affected by the distance.

[0090] For the calculation results of working condition 2: Figure 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 second operating condition.

[0091] At the same time, in this embodiment, in order to analyze the natural cooling of the gas in the wind tunnel, under 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: Figure 15 As shown in the figure, due to the thick wall and large scale of the wind tunnel, the wind tunnel has a certain thermal inertia and the natural cooling rate is slow. After about 1000 minutes of stopping work, the temperature is still above 40°C, which is much higher than the initial temperature of the wind tunnel of 30°C.

[0092] The data obtained above were exported. Based on the spatial distribution characteristics of the temperature in the concrete body and the temporal distribution characteristics during wind tunnel operation, the most unfavorable working condition was selected. 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 conclusions were drawn for the optimal design of the wind tunnel structure:

[0093] 1) Under the 70MW heat rejection power condition, the amount of heat rejection is small and the heat absorption of the heat exchanger is relatively large, so the overall air flow temperature is not high. Due to the presence of the heat exchanger, the heat rejection is basically absorbed by the heat exchanger, and the air flow temperature rises within 5 degrees during the entire operation process. At this time, the temperature inside the cave enclosure structure is relatively 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) The 280MW heat rejection power condition was significantly affected by the initial temperature. When the initial temperature was 30°C, due to the functional relationship between the heat absorption of the heat exchanger and the air temperature, the heat absorption of the heat exchanger was relatively high. During the entire operation, 73% of the heat rejection was absorbed by the heat exchanger, 1% of the heat was dissipated to the outside through the steel structure enclosure, and 17% of the heat was absorbed by the air, causing the wind tunnel air temperature to rise. After 10 minutes of operation, the overall average temperature of the airflow was 50°C, meeting the experimental operating conditions. During this operating condition, the enclosure absorbed a large amount of heat, resulting in a large temperature gradient within it. The temperature difference between the inner and outer surfaces of the tunnel reached 30°C. The thermal stress caused by the temperature gradient must be considered in the structural design.

[0095] 3) In the 280MW heat rejection power condition, when the initial temperature was -3°C, the heat absorption of the heat exchanger was relatively small due to the functional relationship between the heat absorption of the heat exchanger and the air temperature. During the entire operation, only 58% of the heat was absorbed by the heat exchanger, 2% was dissipated to the outside through the steel structure enclosure, and 23% was absorbed by the air, causing the wind tunnel air temperature to rise. After 10 minutes of operation, the overall average airflow temperature was 38°C, meeting the experimental operating conditions. During this operation, the heat absorption of the enclosure increased, resulting in a large temperature gradient within it. The temperature difference between the inner and outer surfaces of the tunnel reached 40°C, the maximum temperature gradient. The thermal stress caused by the temperature gradient must be considered in the structural design.

[0096] 4) Analysis of the calculation results of high-power and long-term operating 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 temperature in the wind tunnel may remain high 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 patterns of the cave body 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 cavity wall under short-time alternating temperature field, characterized in that: The steps include: S1. Identify and calculate relevant parameters for wind tunnel operation; S2. Build a 3D model based on the wind tunnel geometry parameters and process the corner guide vanes. S3. Divide the model into structured grids, establish a hexagonal structured grid model, and refine 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 initial temperature, pressure, and unsteady-state operation time parameters; S6. Call the calculation software to calculate the turbulence and heat transfer process, solve the velocity temperature distribution, and derive the temperature variation pattern of the target area wall surface over time. After deriving the obtained data results, select the most unfavorable working condition based on the spatial distribution characteristics of the temperature in the concrete body in the obtained results and the temporal distribution characteristics as the wind tunnel operates. 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.

2. The method for designing temperature distribution of concrete cavity 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 corresponding wall materials, each cold and heat source in the wind tunnel, and the change law of fluid flow rate under each operation condition of the wind tunnel.

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

4. The method for designing temperature distribution of concrete cavity wall under short-time alternating temperature field according to claim 3 is characterized in that: In step S2, when establishing the 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. 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 size and meshed.

5. The method for designing temperature distribution of concrete cavity 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 cave wall thickness.

6. The method for designing temperature distribution of concrete cavity wall under short-time alternating temperature field according to claim 1 is characterized in that: 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 each grid is within the range of 30 mm to 80 mm.

7. The method for designing temperature distribution of concrete cavity 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 method for designing temperature distribution of concrete cavity 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, and 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 (5) is simplified to a grid boundary.

9. The method for designing temperature distribution of concrete cavity wall under short-time alternating temperature field according to claim 1, characterized in that: In step S6, the calculation software is called to calculate the turbulence and heat transfer process, and the k-epsilon turbulence equation is used to calculate the turbulence in the wind tunnel. At the same time, the energy equation is solved, the heat transfer process is calculated, and the velocity and temperature distribution of the model under the corresponding running time is solved.

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