Optimal design method for fan relay ventilation effect in ultra-long small-section tunnels based on CFD

Abstract

The present invention discloses a CFD-based optimization design method for the relay exhaust effect of fans in ultra-long small-section tunnels, which belongs to the field of tunnel ventilation technology. The method of the present invention includes segmented modeling of the tunnel, the air duct, and the positions where multiple fans are installed in the air duct, meshing the three-dimensional geometric model obtained by modeling, simulating the fan exhaust, importing CFD to calculate and obtain the model parameters and boundary conditions required for the mathematical calculation model to set the operation, changing the relative position of the air duct in the tunnel, and calculating and obtaining the wind speed distribution diagram of the air duct at different positions on the tunnel working surface based on the mathematical calculation model. The air duct at different positions corresponds to different cross-sections on the tunnel working surface. Calculation points are selected at different cross-sections, and the wind speed values ​​of the calculation points are obtained by CFD post-processing. The wind speed values ​​in the air duct at different positions are compared, and the air duct installation position is optimized according to the change of the wind speed value. The present method provides a design basis for the power selection of fans and the optimization of fan and air duct layout during the construction period of ultra-long tunnels.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and in particular to a CFD-based optimization design method for fan relay exhaust effects in an ultra-long small-section tunnel. Background Art

[0002] Due to the limited dimensions of ultra-long, small-section tunnels, construction within the confined space creates significant interference between processes. Drilling, blasting, and slag removal must be performed chronologically within the same working surface. During tunneling, large amounts of suspended dust and hazardous gases are generated near the tunnel face. To ensure good air quality in the workspace for construction workers, these gases and dust must be exhausted from the tunnel or diluted to a safe concentration.

[0003] The current forced-in ventilation system used for tunnel ventilation uses a fan installed at the tunnel exit to direct fresh air through the fan into the air duct, delivering it to the vicinity of the tunnel face. The polluted air near the tunnel face then flows out through the tunnel. Forced-in ventilation also offers high air velocity within the duct, rapid oxygen supply, and a short retention time of fresh air at the working face, making it suitable for tunnel ventilation using drill-and-blast construction techniques. Forced-in ventilation is not suitable for cantilever excavation. Due to tunnel cross-sectional dimensions, axial jet fans cannot be added to enhance ventilation, forcing ventilation to rely solely on exhaust ducts. Exhaust ventilation has a short effective suction range and poor ability to remove dust from the working face. However, it can quickly remove dust near the tunnel face, making it suitable for cantilever excavation, providing a clearer field of view. However, the fan's exhaust efficiency gradually diminishes with increasing tunneling depth, leading to the accumulation of dust concentration and hazardous gases generated by the operation.

[0004] The exhaust ventilation method used in cantilever tunneling construction requires optimization. As tunnel excavation depth increases and air duct lengthens, the fan exhaust efficiency gradually decreases. Currently, the optimal fan installation location is determined based on testing and experience. However, due to the high cost and timeliness of testing, and the uncertainty inherent in engineering experience, the technical difficulties inherent in construction ventilation, such as the small cross-section and long tunnel length, are particularly prominent. Current CFD software, or computational fluid dynamics, is a product of modern fluid mechanics, numerical mathematics, and computer science. Using computers as tools and applying various discretized mathematical methods, it conducts numerical experiments, computer simulations, and analytical research on various fluid mechanics problems to address various practical issues. Therefore, using CFD to analyze the exhaust ventilation effectiveness of ultra-long, small-section tunnels, and to more quickly remove smoke and dust near the tunnel face, is a topic of urgent research. Summary of the Invention

[0005] The purpose of the present invention is to provide a CFD-based optimization design method for the ventilation effect of ultra-long and small-section tunnel fans. Based on the CFD method, the distribution of the air flow field in the air duct and the tunnel is analyzed when multiple fans are relayed in an ultra-long and small-section tunnel. The diffusion law of the gas is analyzed to provide a design basis for the power selection of the fan and the optimization of the fan and duct layout.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The CFD-based optimization design method for fan relay ventilation effect in ultra-long small-section tunnels includes the following steps:

[0008] S1. Model the tunnel and the air duct, and establish a segmented model for the locations where n fans are installed in the air duct. The first segment model is the section from the first fan to the tunnel entrance, and the nth fan installed at the air duct outlet and the tunnel face is the nth segment model. A model is created for the first to nth fans, i.e., the number of fans installed between the first and nth fans is determined based on the depth of the tunnel excavation, and the air duct is extended to obtain a three-dimensional geometric model.

[0009] S2. Meshing the obtained three-dimensional geometric model, and importing the mesh file generated after meshing into CFD simulation software for calculation to obtain a mathematical calculation model;

[0010] S3. Simulate the fan exhaust and set the model parameters and boundary conditions required for the mathematical calculation model:

[0011] 1) The k-ε turbulence model is used as the mathematical calculation model, and the model parameters are the end flow model parameters;

[0012] 2) Boundary condition setting:

[0013] When simulating fan exhaust, define an interface at the fan installation location and define the fan type on the interface. Determine the fan input power based on the fan's air volume-air pressure table.

[0014] The tunnel entrance is a velocity boundary: the type is velocity-inlet, and the direction is along the normal direction of the entrance boundary;

[0015] The duct outlet is a pressure boundary: the type is pressure-outlet, and the relative pressure difference is 0;

[0016] The boundary type of other interfaces between the tunnel and the air duct is wall, which meets the no-slip condition, that is, Vi = 0 m / s;

[0017] S4. Changing the relative position of the air duct in the tunnel: In the CFD simulation software, circles of the same diameter as the air duct are intercepted at different locations on the tunnel cross section as the air duct. Different air duct positions are divided into a circle at the corresponding position. The tunnel working surface is defined along the tunnel axis. Based on the mathematical calculation model, the wind speed distribution diagram of the air duct at different positions on the tunnel working surface is calculated and obtained, including the wind speed distribution diagram of the wind speed vector of the air duct at the tunnel working surface on the horizontal section and the wind speed distribution diagram of the wind speed vector at the tunnel entrance on the vertical section;

[0018] S5. Based on the above wind speed distribution diagram and model parameters, air ducts at different locations correspond to different cross-sections on the tunnel working surface. Calculation points are selected at different cross-sections, and the wind speed values ​​of the calculation points are obtained through CFD post-processing. That is, the wind speed values ​​in the air ducts at different locations are quantitatively obtained. The wind speed values ​​in the air ducts at different locations are compared to obtain the maximum wind speed value, and the optimal air duct installation position is determined.

[0019] As a preferred technical solution of the present invention, in step S1, the distance from the first fan to the tunnel entrance is 20m, the distance from the nth fan to the tunnel face is 3m, and the installation position of the nth fan is the air duct outlet, which is 3m away from the tunnel face.

[0020] As a preferred technical solution of the present invention, step S1 specifically includes the following steps:

[0021] 1) Using 3D modeling software, a 1:1 actual 3D model of the tunnel is established based on the tunnel model dimensions. The tunnel cross-section is a rectangle with a curved top. The parameters of the actual 3D model include tunnel width, height, and non-curved sidewall height.

[0022] 2) Use 3D modeling software to build an actual 3D model of the air duct at the corresponding position in the tunnel, with the parameter involved being the diameter of the air duct;

[0023] 3) Use 3D modeling software to establish multiple actual 3D models of fans at corresponding positions in the air duct.

[0024] Preferably, in step S4, circles of the same diameter as the air duct are intercepted at different positions on the tunnel cross section as the air duct, and different air duct positions are divided into a circle at the corresponding position. Specifically, several circles are set at equal intervals on the central axis of the tunnel cross section. After calculating and comparing the wind speed values ​​at different heights in step S5, the optimal height for the air duct setting is determined. The same circles are set at equal intervals on the left and right sides of the central axis on the horizontal plane at the optimal height. Step S5 is repeated until the optimal installation position of the air duct is determined.

[0025] As a preferred technical solution of the present invention, the design method also includes determining the exhaust power of the fan after establishing the segmented model: determining the minimum exhaust power of the first fan through the first segmented model, and then determining the minimum exhaust power of the second fan through the second segmented model, and so on, until the last, i.e., the nth segmented model is used to determine the minimum exhaust power of the fan installed at the tunnel outlet, P represents the minimum exhaust power, and the minimum exhaust power P of all segmented models is compared, and the maximum value is taken as the power of the fans in all segmented models.

[0026] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The multiple fans installed in the duct are reasonably extended by establishing a segmented model. The number of fans is determined according to the excavation depth. At least two fans are set. Fans are set at a certain distance from the tunnel and at the duct outlet. Ducts are set at different positions in the tunnel cross section. This can verify multiple design schemes in a relatively short time, and the performance parameters of the duct at different installation positions can be easily calculated. The optimal installation position of the duct is determined scientifically and effectively. At the same time, the exhaust power of multiple fans in the duct is determined by the segmented model. After comparison, the maximum exhaust power is obtained and the exhaust power of all fans is unified. Combined with the CFD method, the distribution of the airflow field in the duct and tunnel is analyzed when multiple fans are relayed in an ultra-long small-section tunnel. The gas diffusion law is analyzed to provide a design basis for the power selection of the fan and the optimization of the fan and duct layout.

[0028] 2. Changing the duct position, i.e., adjusting the duct position within the tunnel working face, and calculating and obtaining wind speed distribution maps for each duct position within the tunnel working face based on a mathematical model, including vertical and horizontal cross-sections of the duct near the tunnel working face, revealed a significant increase in wind speed within the duct, significantly improving the exhaust efficiency of harmful gases and dust. The simulation optimization design calculation method of this invention offers the advantages of low cost, high speed, and easy determination of fan power and fan and duct placement. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flow chart of the optimization design method of the present invention;

[0030] Figure 2 This is a schematic diagram of the arrangement of the air ducts in Example 1, in which the relative positions of the air ducts in the tunnel are changed;

[0031] Figure 3 This is a schematic diagram of the optimal position for installing the air duct in Example 1;

[0032] Figure 4 This is a schematic diagram of the installation position of the first fan in comparative example 1;

[0033] Figure 5 This is a schematic diagram of the installation positions of the first fan and the second fan in Example 1;

[0034] Figure 6 The wind speed distribution diagram of the wind speed vector at the tunnel entrance in comparative example 1 on the vertical section;

[0035] Figure 7 The wind speed distribution diagram of the wind speed vector of the air duct near the tunnel working face in comparative example 1 on the horizontal section;

[0036] Figure 8 This is a wind speed distribution diagram of the wind speed vector at the tunnel entrance in Example 1 on the vertical section;

[0037] Figure 9 This is a wind speed distribution diagram of the wind speed vector of the air duct near the tunnel working face in Example 1 on the horizontal section;

[0038] In the figure: 1- tunnel cross section, 2- air duct, 3- fan, 31- first fan, 32- second fan. DETAILED DESCRIPTION

[0039] The following will be combined with the accompanying drawings in this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0040] See Process Figure 1 The CFD-based optimization design method for fan relay ventilation effect in ultra-long small-section tunnels includes the following steps:

[0041] S1. Model the tunnel and the air duct, and establish a segmented model for the locations where n fans are installed in the air duct. The first segment model is the section from the first fan to the tunnel entrance, and the nth fan installed at the air duct outlet and the tunnel face is the nth segment model. A model is created for the first to nth fans, i.e., the number of fans installed between the first and nth fans is determined based on the depth of the tunnel excavation, and the air duct is extended to obtain a three-dimensional geometric model.

[0042] Among them, the distance from the first fan to the tunnel entrance is 20m, the distance from the nth fan to the tunnel face is 3m, and the installation position of the nth fan is the air duct outlet, which is 3m away from the tunnel face.

[0043] The establishment of a 3D geometric model specifically includes the following steps:

[0044] 1) Using 3D modeling software, a 1:1 actual 3D model of the tunnel is established based on the tunnel model dimensions. The tunnel cross-section is a rectangle with a curved top. The parameters of the actual 3D model include tunnel width, height, and non-curved sidewall height.

[0045] 2) Use 3D modeling software to build an actual 3D model of the air duct at the corresponding position in the tunnel, with the parameter involved being the diameter of the air duct;

[0046] 3) Use 3D modeling software to establish multiple actual 3D models of fans at corresponding positions in the air duct.

[0047] S2. Meshing the obtained three-dimensional geometric model, and importing the mesh file generated after meshing into CFD simulation software for calculation to obtain a mathematical calculation model;

[0048] S3. Simulate the fan exhaust and set the model parameters and boundary conditions required for the mathematical calculation model:

[0049] 1) The k-ε turbulence model is used as the mathematical calculation model, and the model parameters are the end flow model parameters;

[0050] 2) Boundary condition setting:

[0051] When simulating fan exhaust, define an interface at the fan installation location and define the fan type on the interface. Determine the fan input power, i.e. the fan's minimum exhaust power, based on the fan's air volume-air pressure table.

[0052] The tunnel entrance is a velocity boundary: the type is velocity-inlet, and the direction is along the normal direction of the entrance boundary;

[0053] The duct outlet is a pressure boundary: the type is pressure-outlet, and the relative pressure difference is 0;

[0054] The boundary type of other interfaces between the tunnel and the air duct is wall, which meets the no-slip condition, that is, Vi = 0 m / s;

[0055] S4. Changing the relative position of the air duct in the tunnel: In the CFD simulation software, circles of the same diameter as the air duct are intercepted at different locations on the tunnel cross section as the air duct. Different air duct positions are divided into a circle at the corresponding position. The tunnel working surface is defined along the tunnel axis. Based on the mathematical calculation model, the wind speed distribution diagram of the air duct at different positions on the tunnel working surface is calculated and obtained, including the wind speed distribution diagram of the wind speed vector of the air duct at the tunnel working surface on the horizontal section and the wind speed distribution diagram of the wind speed vector at the tunnel entrance on the vertical section;

[0056] S5. Based on the above wind speed distribution diagram and model parameters, air ducts at different locations correspond to different cross-sections on the tunnel working surface. Calculation points are selected at different cross-sections, and the wind speed values ​​of the calculation points are obtained through CFD post-processing. That is, the wind speed values ​​in the air ducts at different locations are quantitatively obtained. The wind speed values ​​in the air ducts at different locations are compared to obtain the maximum wind speed value, and the optimal air duct installation position is determined.

[0057] As a preferred implementation of this embodiment, see Figure 2 In step S4, circles of the same diameter as the duct are intercepted at different positions on the tunnel cross section as the ducts. Different duct positions are divided into circles at the corresponding positions. Specifically, several circles are set at equal intervals on the central axis of the tunnel cross section. In step S5, the optimal height for the duct is determined after calculating and comparing the wind speed values ​​at different heights. The same circles are set at equal intervals on the left and right sides of the central axis on the horizontal plane at the optimal height. Step S5 is repeated until the optimal installation position of the duct is determined.

[0058] The design method of this embodiment also includes determining the exhaust power of the fan after establishing the segmented model: determining the minimum exhaust power of the first fan through the first segmented model, and then determining the minimum exhaust power of the second fan through the second segmented model, and so on, until the last, i.e., nth segmented model is used to determine the minimum exhaust power of the fan installed at the tunnel outlet, where P represents the minimum exhaust power. The minimum exhaust power P of all segmented models is compared, and the maximum value is taken as the power of the fans in all segmented models.

[0059] Applying the above specific method to a specific case, the cross section of the ultra-long small-section tunnel is as follows: Figure 2 and Figure 3 As shown, the tunnel width is 4.5m, the height is 4.1m, the air duct diameter is 0.8m, the air duct outlet is 3m away from the tunnel face, and the tunnel excavation reaches 600m. In order to compare and analyze the ventilation effects of a single fan and dual fans, the following comparative test was conducted:

[0060] Comparative Example 1: Simulate single fan exhaust, see Figure 4 , arrange a fan, namely the first fan 31, to perform exhaust operation, and the fan is 20m away from the cave entrance.

[0061] Example 1: n is set to 2, and two segmented models are established to simulate the exhaust of two fans. Figure 5 , arrange the first fan and the second fan for exhaust operation, wherein the first fan is installed in the air duct at the tunnel entrance, 20m away from the tunnel entrance, and the second fan is installed at the air duct outlet and 3m away from the tunnel face.

[0062] When numerically calculating the ventilation conditions based on the CFD method, the number of grid cells used in the meshing process is approximately 8 million, ensuring that the grid is denser on the inner walls of the duct and tunnel. Specifically, when simulating fan ventilation, an interface is defined at the fan location and the fan type is defined on the interface. The fan input power, i.e., the ventilation power, is determined based on the fan's air volume-pressure table (QP table). The flow-pressure table used is shown in Table 1. Other interfaces between the duct and the tunnel are defined as walls or patches, satisfying the no-slip condition, i.e., Vi = 0 m / s.

[0063] Table 1 Flow-pressure table of fan

[0064]

[0065]

[0066] According to the table above, the initial input power of the fan, i.e., the exhaust power, is determined. The exhaust power of the fan used during the test is determined below: For the comparability of the tests, the fan in Comparative Example 1 uses the same exhaust power as the fan in Example 1. According to Example 1, two fans are used to conduct the exhaust test. The first segmented model determines that the minimum exhaust power of the first fan is 37 kW. Then, the second segmented model determines that the minimum exhaust power of the second fan is lower than the minimum exhaust power of the first fan. Therefore, the power of the fans in the two segmented models is set to the minimum exhaust power of the first fan, i.e., 37 kW. Under the same conditions, the exhaust power of the one fan used in Comparative Example 1, i.e., the first fan, is also 37 kW.

[0067] Determine the location of the duct installation: Figure 2 At different locations in the tunnel cross section, circles of the same diameter as the duct were cut as ducts. Different duct locations were divided into circles at the corresponding locations. Specifically, several circles were set at equal intervals on the central axis of the tunnel cross section. Each circle on the central axis had identical circles set at equal intervals on its left and right sides. To ensure comparability of the experiments, the determination of the duct location for the fan in Comparative Example 1 was the same as in Example 1, specifically as follows:

[0068] The tunnel is 4.1m high, 4.5m wide, with an air duct diameter of 0.8m, a non-circular section side wall height of 2.2m, and a tunnel excavation depth of 600m. The air duct is located at a non-circular section side wall height of 2.2m, and the air duct installation position on the tunnel centerline is x0=2.25m, y=2.2m, and so on: the fan installation position x=2.25m on the tunnel centerline remains unchanged, and the height y from bottom to top is y1=0.4m, y2=1.2m, y3=1.6m, y4=2.2m, y5=2.6m, corresponding to the fan positions on the left and right sides of y1 to y5 from left to right are x1=0.65m, x2=1.45m, x0=2.25m, x3=3.05m, x4=3.85m. In actual practice, in this embodiment, pedestrians or vehicles are required within 2 m above the tunnel ground, and the air duct is set in the upper middle part of the tunnel. The height y can be directly selected from bottom to top as y4 = 2.2 m and y5 = 2.6 m. At the same height, the fan positions on the left and right sides corresponding to y4 to y5 are x1 = 0.65 m, x2 = 1.45 m, x0 = 2.25 m, x3 = 3.05 m, and x4 = 3.85 m from left to right.

[0069] The optimized design method of the present application was used to simulate fan exhaust at the above-mentioned different fan positions. As in Example 1, two fans were used for simulated exhaust, both of which were axial flow fans. The ventilation simulation results at different fan heights on the tunnel centerline and at the same height in the horizontal direction were obtained. See Table 2 for details:

[0070] Table 2 Ventilation simulation results at different duct positions

[0071]

[0072]

[0073] As can be seen from Table 2, when the air duct is arranged at the top of the tunnel (height 2.6m), the axial flow energy loss increases again when it is close to the top of the tunnel, and the fan ventilation efficiency decreases. Determine y4 = 2.2m as the optimal height position, and take 2.2m as the arrangement height of the air duct; further simulate the horizontal ventilation efficiency: x1 = 0.65m, x2 = 1.45m, x0 = 2.25m, x3 = 3.05m, x4 = 3.85m. Due to the influence of the tunnel wall, theoretically, the ventilation efficiency of the air duct position on the central axis of the tunnel is the best, and the air flow energy loss in the middle is the smallest and more uniform. However, due to factors such as the installation of the air compressor air supply duct and electrical safety in the lower right corner of the tunnel cross section, the simulation results show that the ventilation efficiency is best close to the central axis of the tunnel to the right, that is, Figure 3 The fan position shown is x4=3.85m, y4=2.2m.

[0074] The air duct installation positions of Comparative Example 1 and Example 1 were determined to be x4=3.85m and y4=2.2m, and the following comparative tests were performed:

[0075] Comparative Example 1: The same working conditions as in Comparative Example 1 are set, the tunnel excavation depth is 600m, and one fan is used for exhaust at the tunnel entrance. Figure 6 is the distribution of wind speed vector at the tunnel entrance on the vertical section, Figure 7 This is the horizontal cross-sectional distribution of the wind speed vector in the duct near the tunnel working face. It shows that the wind inside the duct is drawn out of the tunnel, with the maximum wind speed inside the duct reaching 11.3 m / s. Fresh air from the tunnel enters the tunnel at a speed of less than 1 m / s. The wind speed gradually decreases at the duct outlet, and the wind inside the tunnel is drawn into the duct. The wind speed inside the duct near the tunnel working face is as low as 4.68 m / s, indicating that the wind speed gradually decreases along the approximately 600 m of duct. Therefore, it is possible to consider adding fans and implementing fan relays to increase wind speed and promote the rapid discharge of pollutants.

[0076] Comparative Example 2: The same working conditions as Comparative Example 1 are set, the tunnel excavation depth is 500m, and a fan is used for exhaust at the tunnel entrance. The wind inside the duct is extracted out of the tunnel, and the maximum wind speed inside the duct is 15.8m / s. The fresh air in the tunnel enters the tunnel at a speed of less than 1m / s; the wind speed gradually decreases when it reaches the duct outlet, and the wind inside the tunnel is extracted into the duct. The minimum wind speed inside the duct near the tunnel working face is 8.54m / s, indicating that the wind speed gradually decays along the duct.

[0077] A comparative analysis of Example 1 and Example 2 shows that: when the tunnel has only one exhaust fan, the minimum wind speed inside the air duct near the tunnel working face is 8.54m / s when the excavation depth is 500m, and the minimum wind speed inside the air duct near the tunnel working face is 4.68m / s when the excavation depth is 600m. As the excavation depth increases, the wind speed inside the air duct near the tunnel working face decreases significantly. In order to ensure the ventilation environment at the construction site, it is necessary to adopt fan relay to increase the wind speed in the tunnel.

[0078] Example 1: The same working conditions as in Example 1 are set, the tunnel excavation depth is 600m, and two fans are used for exhaust at the tunnel entrance. Figure 8 is the distribution of wind speed vector at the tunnel entrance on the vertical section, Figure 9 This is the distribution diagram of the wind speed vector of the air duct near the tunnel working face on the horizontal section. It can be seen that after two fans are installed in the tunnel, the wind speed inside the pipe near the tunnel entrance is 14.7m / s. The wind speed increases when it reaches the air duct outlet. The wind inside the tunnel is drawn into the air duct, and the wind speed inside the air duct near the tunnel working face reaches 21m / s.

[0079] A comparative analysis of Example 1 and Comparative Example 1 shows that adding two exhaust fans to the fan duct near the tunnel working face significantly increases the wind speed inside the duct compared to adding one fan, greatly improving the exhaust efficiency of harmful gases and dust.

[0080] Based on the above Comparative Example 1, Comparative Example 2 and Example 1, new Comparative Example 3, Example 2 and Example 3 are added. Fans are set at different excavation depths. Tests are conducted under the same working conditions to obtain calculated values ​​of wind duct wind speeds near the tunnel working face at different excavation depths, as well as corresponding measured values. See Table 3 for details:

[0081] Table 3 Comparison of calculated and measured wind speeds in the air duct near the tunnel working face at different excavation depths

[0082]

[0083] According to the comparison of the calculated values ​​and the measured values, when a single fan is used, the calculated and measured wind speed values ​​of the air duct near the tunnel working face gradually decrease when the excavation depth increases from 500 to 800 meters. It can be seen that the wind speed value gradually decays with the increase of tunnel excavation depth, and the decay amplitude is large, which cannot meet the requirements of the underground tunnel construction working environment. It can be judged that the air duct should be extended and more fans should be added; after the use of two fans, the calculated and measured values ​​inside the air duct near the tunnel working face gradually decay when the excavation depth increases from 500 to 800 meters, but the decay rate is relatively slow. The exhaust effect of the fan does not significantly decay with the increase of tunnel excavation depth, which can meet the requirements of the underground tunnel construction working environment. After subsequent excavation of 1200m, 2000m or deeper, after continuing to extend the air duct and add fans, the wind speed inside the air duct near the tunnel working face is measured to reach more than 20m / s. The exhaust effect of the fan does not significantly decay with the increase of tunnel excavation depth, which can meet the requirements of the underground tunnel construction working environment. Therefore, the segmented model established in this application can simulate actual working conditions, simplify the test process, and verify multiple design schemes in a relatively short period of time.

[0084] In addition, wind speed was measured in the tunnel with exhaust ventilation. Table 3 shows the measured wind speed values ​​corresponding to the single and double fan settings at different excavation depths. Comparison shows that the on-site measured values ​​are smaller than the calculated values. Due to factors such as installation twisting of the on-site air ducts, air leakage, misalignment of the air duct connections, and rough air duct walls, the ventilation resistance is increased, and the wind speed attenuation on site is more obvious. The measured wind speed is smaller than the calculated value. Through table verification, it can be seen that the deviation between the calculated value and the measured value is ±20%. Subsequently, the measured value can be approached by adding the deviation value to the corresponding calculated value.

[0085] In summary, this application analyzes the distribution of the air duct and the air flow field in the tunnel under the ventilation conditions of the ultra-long small-section tunnel by combining the CFD method, and configures the appropriate number of fans according to the distribution law of the air flow field at different excavation depths, thereby reducing costs and increasing efficiency for the project while ensuring the working environment of the face. By combining the CFD method to analyze the distribution of the air duct and the air flow field in the tunnel under the conditions of multiple fans relaying ventilation in the ultra-long small-section tunnel, the fan can be set at a certain distance from the tunnel, or at the air duct outlet to achieve a reasonable extension of the fan. It can verify multiple design schemes in a relatively short time, and can easily calculate the performance parameters of the air duct under different installation positions. It can scientifically and effectively determine the optimal installation position of the air duct, and provide a design basis for the power selection of the fan and the optimization of the fan and air duct layout.

Claims

1. CFD-based optimization design method for fan relay ventilation effect in ultra-long small-section tunnels, characterized by The following steps are involved: S1. Model the tunnel and the air duct, and establish a segmented model for the locations where n fans are installed in the air duct. The first segment model is the section from the first fan to the tunnel entrance, and the nth fan installed at the air duct outlet and the tunnel face is the nth segment model. A model is created for the first to nth fans, i.e., the number of fans installed between the first and nth fans is determined based on the depth of the tunnel excavation, and the air duct is extended to obtain a three-dimensional geometric model. S2. Meshing the obtained three-dimensional geometric model, and importing the mesh file generated after meshing into CFD simulation software for calculation to obtain a mathematical calculation model; S3. Simulate the fan exhaust and set the model parameters and boundary conditions required for the mathematical calculation model: 1) The k-ε turbulence model is used as the mathematical calculation model, and the model parameters are the end flow model parameters; 2) Boundary condition setting: When simulating fan exhaust, define an interface at the fan installation location and define the fan type on the interface. Determine the fan input power based on the fan's air volume-air pressure table. The tunnel entrance is a velocity boundary: the type is velocity-inlet, and the direction is along the normal direction of the entrance boundary; The duct outlet is a pressure boundary: the type is pressure-outlet, and the relative pressure difference is 0; The boundary type of other interfaces between the tunnel and the air duct is wall, which meets the no-slip condition, that is, Vi = 0 m / s; S4. Changing the relative position of the air duct in the tunnel: In the CFD simulation software, circles of the same diameter as the air duct are intercepted at different locations on the tunnel cross section as the air duct. Different air duct positions are divided into a circle at the corresponding position. The tunnel working surface is defined along the tunnel axis. Based on the mathematical calculation model, the wind speed distribution diagram of the air duct at different positions on the tunnel working surface is calculated and obtained, including the wind speed distribution diagram of the wind speed vector of the air duct at the tunnel working surface on the horizontal section and the wind speed distribution diagram of the wind speed vector at the tunnel entrance on the vertical section; S5. Based on the above wind speed distribution diagram and model parameters, air ducts at different locations correspond to different cross-sections on the tunnel working surface. Calculation points are selected at different cross-sections, and the wind speed values ​​of the calculation points are obtained through CFD post-processing. That is, the wind speed values ​​in the air ducts at different locations are quantitatively obtained. The wind speed values ​​in the air ducts at different locations are compared to obtain the maximum wind speed value, and the optimal air duct installation position is determined.

2. The CFD-based optimization design method for fan relay ventilation effect in ultra-long small-section tunnels according to claim 1 is characterized by: In step S1, the distance between the first fan and the tunnel entrance is 20m, the distance between the nth fan and the tunnel face is 3m, and the installation position of the nth fan is the air duct outlet, which is 3m away from the tunnel face.

3. The CFD-based optimization design method for fan relay ventilation effect in ultra-long small-section tunnels according to claim 1 is characterized in that The step S1 specifically includes the following steps: 1) Using 3D modeling software, a 1:1 actual 3D model of the tunnel is established based on the tunnel model dimensions. The tunnel cross-section is a rectangle with a curved top. The parameters of the actual 3D model include tunnel width, height, and non-curved sidewall height. 2) Use 3D modeling software to build an actual 3D model of the air duct at the corresponding position in the tunnel, with the parameter involved being the diameter of the air duct; 3) Use 3D modeling software to establish multiple actual 3D models of fans at corresponding positions in the air duct.

4. The CFD-based optimization design method for fan relay ventilation effect in ultra-long small-section tunnels according to claim 1 is characterized in that In step S4, circles of the same diameter as the air duct are intercepted at different positions on the tunnel cross section as the air duct, and different air duct positions are divided into a circle at the corresponding position: specifically, several circles are set at equal intervals on the central axis of the tunnel cross section, and the optimal height for the air duct setting is determined after calculating and comparing the wind speed values ​​at different heights in step S5. The same circles are set at equal intervals on the left and right sides of the central axis on the horizontal plane at the optimal height, and step S5 is repeated until the optimal installation position of the air duct is determined.

5. The CFD-based optimization design method for fan relay ventilation effect in ultra-long small-section tunnels according to claim 1 is characterized in that It also includes the determination of the fan exhaust power after establishing the segmented model: the minimum exhaust power of the first fan is determined by the first segmented model, and then the minimum exhaust power of the second fan is determined by the second segmented model, and so on, until the last, that is, the nth segmented model is used to determine the minimum exhaust power of the fan installed at the tunnel outlet. P represents the minimum exhaust power. The minimum exhaust power P of all segmented models is compared, and the maximum value is taken as the power of the fans in all segmented models.

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