An optimization design method for spacing of connecting flues in a super-long highway tunnel crossing a sea

Abstract

This invention discloses an optimized design method for the spacing of connecting smoke ducts in extra-long cross-sea highway tunnels, comprising: establishing multiple tunnel models with different numbering using ICEM CFD software, generating corresponding msh mesh files by numbering the tunnel models with different connecting smoke duct spacings; importing the msh mesh files with different numberings into Fluent software, simulating the spread of smoke in the tunnel using Fluent software, and saving the data as dat data with different numberings; importing the dat files with different numberings into CFD-Post software, and obtaining the distance L from the fire source to the fire source from the point farthest from the fire source using CFD-Post software. 60i The smoke extraction efficiency η of each opened smoke exhaust port i Select L 60i ≤2L, and η i For tunnel models with ≥95% efficiency, the resistance reduction rate ξ of adjacent numbered tunnel models is calculated sequentially. The tunnel model with the lowest frictional resistance is selected to obtain the optimal spacing for connecting flues. The evaluation criteria of this invention are effective, and the optimization is reasonable. The parameters are set according to the actual engineering conditions of the tunnel, making it suitable for extra-long cross-sea tunnels where it is difficult to install vertical shafts.

Description

Technical Field

[0001] This invention relates to the field of tunnel fire smoke control technology, specifically to an optimized design method for the spacing of connecting smoke ducts in extra-long cross-sea highway tunnels. Background Technology

[0002] With the rapid development of my country's economy and the improvement of living standards, urban underground space has been effectively developed and utilized, greatly accelerating its development. Due to development needs, more and more urban transportation systems are constructing tunnels under rivers, lakes, and seas, leading to rapid development in underwater tunnel construction. In recent years, major cities have successively built numerous underwater tunnels, and in the future, underwater tunnel development will continue with even stronger momentum.

[0003] To accelerate cross-strait economic development and alleviate pressure on other transportation hubs, a large number of larger-scale cross-sea tunnels will emerge, trending towards greater length and more ramps or branching points. However, for ultra-long cross-sea tunnels, due to their excessive length, reasonable ventilation zone division is necessary. This can be achieved by using several vertical shafts for air supply and exhaust, reducing the length of ventilation zones to replace polluted air and ensure a good driving environment within the tunnel. Considering the difficulties of setting up vertical shafts in the sea, a novel ventilation scheme without shafts is proposed. Given the lack of clear domestic and international standards guiding the construction of connecting flues in ultra-long cross-sea tunnels, this invention proposes an optimized design method for the spacing of connecting flues in extra-long cross-sea highway tunnels. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide an optimized design method for the spacing of connecting smoke ducts in extra-long cross-sea highway tunnels. By determining the corresponding evaluation model for the spacing of connecting smoke ducts and optimizing the setting spacing of the connecting smoke ducts, the method can maximize the safety of personnel evacuation and the effectiveness of smoke exhaust while ensuring cost reduction.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: An optimized design method for the spacing of connecting flues in extra-long cross-sea highway tunnels includes the following steps: Step 1: Use ICEM CFD software to create multiple tunnel models with the same length and opening size. Each tunnel model includes two parallel vehicular tunnels designed according to the design parameters. Smoke exhaust ducts are set above the roof of the vehicular tunnels. Smoke exhaust outlets are arranged at equal intervals according to the design spacing on the roof of the vehicular tunnels. Different numbers of tunnel models are set with different numbers of vehicular cross passages in an increasing order. Adjacent vehicular cross passages are equidistant. A connecting smoke duct is set above each vehicular cross passage according to the design parameters. Tunnel models with different connecting smoke duct spacings are numbered and corresponding msh mesh files are generated. The number of vehicular cross passages of adjacent numbered tunnel models differs by n. Step 2: Import the msh mesh files with different numbers into Fluent software. Use Fluent software to set fire sources with the same power at the same location in different models. The smoke exhaust volume of the fire sources is the same. Open the same number of smoke exhaust ports in the upstream and downstream directions of the fire sources. Calculate the fire source model to simulate the spread of smoke in the driving tunnel and save it as dat data format with different numbers. Step 3: Import the .dat files with different numbers into the CFD-Post software. Use the CFD-Post software to uniformly set several points at the top of the tunnel of different models to extract temperature values, and set slices at the positions of the smoke exhaust vents of the tunnel of different models to extract smoke exhaust volume values. Set the width of the slices to be the same as that of the tunnel and the height of each slice to be the same. Temperature values ​​were extracted from various points, and the distance L from the fire source was calculated among the points with temperatures exceeding 60℃ in the tunnel model with different connecting flue spacing. 60i The amount of carbon monoxide generated is extracted from each slice, and the ratio of carbon monoxide absorbed by each open smoke exhaust vent to the amount of carbon monoxide generated by the fire is calculated to obtain the smoke exhaust efficiency η of each open smoke exhaust vent in the tunnel model with different connecting smoke duct spacing. i Calculate the sum of the local resistance coefficient and friction resistance coefficient of the smoke exhaust channel in the tunnel model with different connecting smoke duct spacings, i.e., the friction resistance coefficient ∆ξ of the tunnel model with different connecting smoke duct spacings. i ; Step 4, Select L 60i ≤2L, and η i ≥95% tunnel model, 2L is the length of the area covered by the set open smoke vent along the longitudinal direction of the tunnel; Step 5: Calculate the resistance reduction rate ξ for adjacent tunnel models, i.e., the friction resistance coefficient ∆ξ of the i-th tunnel model. i The frictional resistance coefficient ∆ξ of the (i+n)th tunnel model i+n The difference between ∆ξ and i If the ratio of ξ is not greater than 5%, then the tunnel model numbered i+n is removed. Step 6: Select the tunnel model with the lowest frictional resistance from the different tunnel models selected in Step 5 to obtain the optimal spacing for the connecting flue.

[0006] Furthermore, the local drag coefficient α is calculated as follows:

[0007]

[0008]

[0009]

[0010] In the formula: α is the local resistance coefficient at the connecting flue, α AB α AC α AE The local drag coefficients P for sections AA to BB, AA to CC, and AA to EE are respectively. A P B P C P E These are the static pressures at sections AA, BB, CC, and EE, respectively, V. A V B V C V E These are the flue gas velocities at cross sections AA, BB, CC, and EE, respectively, and D. A D B D C D E These are the equivalent diameters of sections AA, BB, CC, and EE, respectively, which are the perimeters of the sections. A L B L C L E These are the distances between section AA and the nearest flue gas inlet on the flue gas inflow side, section BB and the nearest flue gas inlet on the flue gas inflow side, section EE and the nearest flue gas inlet on the flue gas inflow side, and the distance from section CC to the flue gas exhaust channel, λ. A , λ B , λ C , λ E They are respectively with L A Equal length vehicular tunnel section, and L B Equal length smoke exhaust duct section, connecting smoke duct section of equal length with Lc, and L EThe friction coefficient of the smoke exhaust duct section of equal length, section AA is the end face of the driving tunnel section between adjacent connecting smoke ducts in the tunnel model that is close to the smoke inflow side, sections BB and EE are the end faces of the smoke exhaust duct above section AA that are close to section AA and the end faces that are far from section AA, and section CC is the end face of the smoke outflow end in the connecting smoke duct.

[0011] Furthermore, the friction coefficient λ is calculated as follows:

[0012] Where: ∆ - average wall roughness; D - equivalent diameter of tunnel cross section.

[0013] Furthermore, the heat source power is set at 50MW, and the smoke exhaust volume is 360m³. 3 / s.

[0014] Furthermore, the fire source is positioned between at least two smoke vents, and the number of smoke vents is even.

[0015] Furthermore, based on the most unfavorable scenario of a highway tunnel fire, the fire source is located in the middle of the highway tunnel section between adjacent connecting smoke ducts.

[0016] Furthermore, in Fluent software, the fire source was set as the mass-flow inlet, the tunnel wall was set as the wall boundary condition with a roughness of 2.5 mm, the SIMPLE pressure correlation algorithm was selected as the separate solver, the pressure discretization scheme in the simulation was set to body force weighted, the momentum, carbon dioxide and energy were calculated using the second-order upwind scheme, and the turbulent kinetic energy and turbulent dissipation rate were calculated using the first-order upwind scheme. The default values ​​of the relaxation factors for pressure, momentum, turbulent kinetic energy and turbulent dissipation rate were reduced to 0.3, 0.5, 0.5 and 0.5 respectively. The simulation calculation time was 1200 s and the model was run to simulate the spread of smoke in the driving tunnel.

[0017] Compared with existing technologies, the advantages of this invention are: the design method is simple, the evaluation indicators are novel and effective, and parameters can be set according to the actual engineering conditions of the tunnel, making it suitable for extra-long cross-sea tunnels where vertical shafts are difficult to install. Currently, there is no design method for connecting smoke ducts in extra-long cross-sea tunnels. This method, based on a performance-based optimization evaluation model for connecting smoke duct spacing, verifies the rationality of the new model, optimizes the spacing of connecting smoke ducts in extra-long cross-sea tunnels, and the results are innovative and have practical engineering significance. It provides a reference for the control of smoke and fire hazards at the longitudinal top of extra-long tunnels and for the safe evacuation of personnel. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the tunnel bidirectional balanced key smoke exhaust mode in this invention; Figure 2 This is a flowchart of the performance-based evaluation process for the spacing optimization of connecting flues in this invention; Figure 3 This is a schematic diagram of the tunnel model established in this invention; Figure 4 This is a schematic diagram showing the setup of tunnel flue gas propagation temperature data extraction points in this invention; where Generic indicates the use of a general type. Figure 5 This is a schematic diagram of tunnel smoke propagation temperature data extraction in this invention; where Current (SI) indicates that the extracted data uses internationally accepted units, and Export Geometry Information indicates confirmation of exported geometric information; Figure 6 This is a table of tunnel smoke propagation temperature data in this invention, where X, Y, and Z are the vertical axis, horizontal axis, and vertical axis in the tunnel model, respectively. The three points determine a location in the model and the temperature at that location is obtained. Figure 7 This is a schematic diagram showing the setting of the data extraction section for the smoke exhaust outlet in this invention; Figure 8 This is a schematic diagram of the data extraction formula for the smoke exhaust outlet in this invention; Figure 9 This is a diagram showing the relationship between the frictional resistance coefficient and the spacing of the connecting flues in this invention. Figure 10 For the theoretical calculation model of local drag coefficient, (a) is a schematic diagram of tunnel airflow, and (b) is a schematic diagram of characteristic cross-section; Figure 11 This is a schematic diagram of the cross-sectional setting for static pressure data extraction in this invention; Figure 12 This is a schematic diagram of the cross-sectional setting for flue gas velocity data extraction in this invention. Detailed Implementation

[0019] The principles and features of the present invention are described below with reference to the accompanying drawings and specific embodiments. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0020] like Figures 1 to 10 As shown, this invention provides an optimized design method for the spacing of connecting flues in extra-long cross-sea highway tunnels, comprising the following steps: S1: A new key smoke exhaust mode is proposed, which involves longitudinally setting connecting smoke ducts at intervals on the key smoke exhaust ducts of two-pipe tunnels. This overcomes the problem of insufficient suction power in the key smoke exhaust mode at the top of extra-long tunnels, effectively reduces the resistance of the ventilation system, and improves the timeliness of emergency disaster smoke exhaust.

[0021] To obtain the optimal design results for the spacing of connecting flues, multiple tunnel models with the same length and opening size were established. Each tunnel model included two parallel vehicular tunnels designed according to the design parameters. Smoke exhaust ducts were set above the roof of the vehicular tunnels, and smoke exhaust outlets were arranged at equal intervals according to the design spacing on the roof of the vehicular tunnels. Different numbers of tunnel models were set with different numbers of vehicular cross passages in an increasing order. Adjacent vehicular cross passages were equidistant from each other, and a connecting flue was set above each vehicular cross passage according to the design parameters. S2: Based on the different tunnel models obtained above, and considering personnel evacuation safety and smoke exhaust effectiveness, a performance-based optimization evaluation model for the spacing of connecting smoke ducts is constructed. Performance-based evaluation mainly refers to the evaluation model taking into account engineering realities, and the setting of connecting smoke ducts taking into account cost-effectiveness. In step S2, based on personnel evacuation safety and smoke extraction effectiveness, the smoke spread range L is selected. 60 The three indicators are smoke extraction efficiency η, resistance reduction rate ξ, and air spread range L. 60 Smoke extraction efficiency η most directly reflects the optimizing effect of connecting flues on fire smoke extraction and is the most basic indicator for meeting fire smoke control requirements. Resistance reduction rate ξ is an innovative indicator that combines the friction resistance coefficient with the spacing of connecting flues, aiming to shorten the spacing of connecting flues from an engineering perspective. (1) Smoke spread range L 60 When the longitudinal wind speed vs ≥ the critical wind speed vc, the smoke blows downwind, but at the same time, the smoke downstream of the fire source cannot cross the open exhaust port. This achieves the control principle that "longitudinal ventilation can effectively suppress smoke backflow, keeping the smoke upstream of the fire source within a controllable range; and smoke overflow is restricted at the downstream open exhaust port." The criterion for smoke spread to this location is the position of the 60°C smoke front below the flue plate, and its spread range is denoted as L. 60 The range of smoke spread is L. 60 It should be less than or equal to twice the distance L from the heat source to the open smoke exhaust vent, i.e., L 60 ≤2L; (2) Smoke exhaust efficiency η Smoke extraction efficiency is used to characterize how much smoke is expelled from a fire. Higher smoke extraction efficiency means more smoke is expelled, thus better reducing the impact of smoke on evacuation. Therefore, the smoke extraction efficiency of a good smoke extraction system should satisfy η≥95%. (3) Drag reduction rate ξ Based on the functional relationship between the spacing of connecting flues and the tunnel friction resistance coefficient, a resistance reduction rate ξ is proposed. Obviously, the overall friction resistance of the tunnel smoke exhaust system will continuously decrease as the spacing of connecting flues decreases. However, considering the actual engineering situation, the number of connecting flues cannot be increased indefinitely. In order to determine a suitable resistance reduction rate value, it is stipulated that if the resistance reduction rate is less than 5% after shortening the spacing of connecting flues, it can be considered that the influence of the connecting flue spacing on the resistance of the tunnel smoke exhaust system is negligible, that is, this factor is no longer considered. The resistance reduction rate of an excellent smoke exhaust tunnel should satisfy ξ≥5%.

[0022]

[0023]

[0024] Where: ξ - drag reduction rate (%), ∆ξ i - The unit frictional resistance coefficient (N·s) for each model 2 / m 8 ), i - the model number. The unit friction resistance coefficient of each model is obtained by adding the friction resistance coefficient of a pipe segment and the local resistance coefficient of a connecting flue in the following formula; the pipe segment is the area between adjacent vehicular crosswalks in the tunnel model. For ease of calculation, the tunnel model is divided with the midpoint of each pipe segment as the dividing line, such as Figure 10 As shown in Figure a, the area between the midpoints of adjacent pipe segments is designated as a standard pipe segment. The unit friction resistance coefficient of each standard pipe segment is the same as that of any other pipe segment. Each standard pipe segment includes a connecting flue and a vehicular crosswalk, as well as half-sections of the vehicular tunnel on both sides of the crosswalk. Smoke exhaust ducts are installed above the roof of the vehicular tunnels, such as... Figure 10 As shown in section b, section AA is the starting section where flue gas flows into the driving tunnel in the standard pipe section, and it is equal to other sections of the driving tunnel. Sections BB and EE are the sections at both ends of the smoke exhaust channel in the standard pipe section, and they are equal to other sections of the smoke exhaust channel. Section CC is the section at the flue gas outlet in the connecting flue, and it is equal to other sections of the connecting flue.

[0025]

[0026] In the formula: - is the local resistance coefficient at each connecting flue; λ- is the friction resistance coefficient along each pipe section;

[0027] Where: ∆ - average wall roughness, referring to the "Detailed Rules for Ventilation Design of Highway Tunnels", the smoothness of the tunnel concrete wall is generally good, and the roughness is taken as 2.5mm; D - equivalent diameter of the tunnel section, m; the surface roughness of each standard pipe section is equal to the equivalent diameter of the tunnel section, and the friction coefficient of each pipe section is equal. The local drag coefficient α at each connecting flue is obtained according to the following Bernoulli equation: The theoretical calculation model for the local resistance coefficient at the connecting flue is as follows:

[0028]

[0029]

[0030]

[0031] In the formula: α is the local resistance coefficient at the connecting flue, α AB α AC α AE The local drag coefficients P for sections AA to BB, AA to CC, and AA to EE are respectively. A P B P C P E These are the static pressures at sections AA, BB, CC, and EE, respectively, V. A V B V C V E These are the flue gas velocities at cross sections AA, BB, CC, and EE, respectively, and D. A D B D C D E These are the equivalent diameters of sections AA, BB, CC, and EE, respectively, which are the perimeters of the sections. A L B L C L E These are the distances between section AA and the nearest flue gas inlet on the flue gas inflow side, section BB and the nearest flue gas inlet on the flue gas inflow side, section EE and the nearest flue gas inlet on the flue gas inflow side, and the distance from section CC to the flue gas exhaust channel, λ. A , λ B , λ C , λ E They are the L-shaped driving tunnels. A Section, smoke exhaust duct L B Section, connecting flue Lc section, smoke exhaust duct L E The friction coefficient along the section.

[0032] In step S2, the optimization evaluation model for the spacing of the connecting flues is as follows: ; S3: Since there are currently no precedents for setting up connecting smoke ducts in highway tunnels, and the connecting smoke ducts in extra-long tunnels are correspondingly located above the vehicular cross passages, the spacing of the vehicular cross passages can be used as a reference for setting up connecting smoke ducts. The design of the spacing of vehicular cross passages in domestic highway tunnels is shown in Table 1. Article 12.1.6 of the "Code for Fire Protection Design of Buildings" (GB50016-2014): For twin-hole tunnels for motor vehicles, the setting of vehicular cross passages or vehicular evacuation passages shall comply with the following provisions: ① Underwater tunnels should preferably be equipped with vehicular cross passages or vehicular evacuation passages, and the spacing between the vehicular cross passages and the interval between the tunnel entrance to the vehicular evacuation passage should preferably be 1000m~1500m; ② The vehicular cross passages should be arranged along the direction perpendicular to the length of the tunnel and should lead to the adjacent tunnel.

[0033] Table 1 Survey of Crosspass Spacing in Highway Tunnels

[0034] Table 1 shows that the spacing of cross passages in highway tunnels is in the range of 500m to 1500m. When the tunnel length is too long, considering factors such as geological structure stability and engineering volume, the spacing of connecting passages should be appropriately increased. Therefore, the spacing of connecting passages is set between 750m and 2250m.

[0035] S4: Fluent numerical simulation section: Step 1. Determine the tunnel model to be studied according to step S1, as shown in the table below; Table 2. Operating Conditions of Connecting Flues

[0036] J02 is equivalent to a connecting flue spacing of 1125m.

[0037] A corresponding tunnel model was built using ICEM CFD software, such as a model of an extra-long cross-sea highway tunnel with a length of 13.9 km, a width of 15 m, and a height of 8.5 m. Smoke vents were located on the tunnel roof, with a transverse length of 5 m and a longitudinal length of 1.2 m, and a spacing of 60 m between them. Figure 3 As shown, it generates the corresponding msh mesh file.

[0038] Step 2. Import the above msh file into Fluent software. Set the corresponding fire source power and smoke exhaust parameters in Table 2 for the model. Take the most unfavorable case of a highway tunnel fire, i.e., a heavy vehicle fire, with the fire source located in the middle of the tunnel, and a fire source power of 50MW. Set the fire source to be located in the middle of the six smoke exhaust outlets (the fire source being located in the middle of the tunnel is considered the most unfavorable smoke exhaust and ventilation situation). Set the fire source as mass-flow inlet. Set the tunnel wall as wall (wall boundary condition) and the roughness to 2.5mm. Select the SIMPLE pressure correlation algorithm as the separate solver. Set the pressure discretization scheme in the simulation to body force weighted, and use the second order upwind scheme for momentum, carbon dioxide, and energy. Use the first order upwind scheme for turbulent kinetic energy and turbulent dissipation rate. To ensure computational convergence, the default values ​​for relaxation factors of pressure, momentum, turbulent kinetic energy, and turbulent dissipation rate were reduced to 0.3, 0.5, 0.5, and 0.5, respectively. The simulation was performed for 1200 seconds, and the model was run, with the corresponding .dat data file saved.

[0039] Step 3. Import the above .dat file into CFD-Post to extract the data required for the three evaluation indicators in step S2. Using the Location function in CFD-Post, set the area Line for extracting temperature values ​​on the top of the roadway according to the corresponding tunnel model (the Line only needs to be distributed in the smoke exhaust outlet section controlling the smoke, such as within 150m on both sides of the fire source and within the range of six smoke exhaust outlets in this step). Determine the position of the Line through Point1 and Point2, and determine the number of points to extract data by setting Samples, for example, 601 points. Figure 4 As shown. Then, through the Export option in the File menu of the software, select the corresponding Line in Location, and generate an excal data table in the form of temperature, as shown. Figure 5 As shown. The resulting excal data table is as follows. Figure 6 As shown, subtracting 273.15 from the Kelvin temperature in the Temperature column gives the Celsius temperature. The range of temperatures exceeding 60°C can then be calculated and compared with the flue gas propagation range L. 60 The indicators were compared; using the Location function in CFD-Post, a smoke exhaust outlet slice plane was set at the smoke exhaust outlet location to extract smoke exhaust volume values ​​based on the corresponding tunnel model. The smoke exhaust outlet slice was set by selecting the insertion height after determining the plane, such as... Figure 7As shown, in the Table Viewer interface of CFD-Post, create a New Table to extract data from the corresponding exhaust outlet section. Select the areaAve option in the Function menu to determine the required formula to take the average value of the area. Within the formula's parentheses, select Co.Mass Fraction in the Variable menu to indicate that the extracted content is carbon monoxide generation. Finally, after the @ symbol at the end of the formula, select the name of the corresponding slice in the Location menu to extract the carbon monoxide generation at the exhaust outlet location. Figure 8 As shown, by calculating the ratio of carbon monoxide absorbed by each smoke exhaust outlet to the amount of carbon monoxide generated by the fire, the smoke exhaust efficiency η of each smoke exhaust outlet can be obtained. Similarly, using the Location function in CFD-Post, cross-sections for extracting flue gas velocity and static pressure values ​​are set based on the location of the connecting flue in the corresponding tunnel model and the location of the midpoint of the vehicular tunnel between adjacent connecting flues. Figure 10 Sections AA, BB, CC, and EE, as shown in section a, are as follows: Figure 11 and Figure 12 As shown, in the Table Viewer interface of CFD-Post, create a New Table to extract data from the corresponding exhaust port section. Select the areaAve option in the Function option to determine the required formula to take the average value of the area. In the parentheses inside the formula, select pressure and velocity in the Variable option to indicate that the extracted content is static pressure and flue gas velocity. Finally, after @ at the end of the formula, select the name of the corresponding section in the Location option to extract the static pressure and flue gas velocity at the section location.

[0040] Finally, the sum of the local resistance coefficient and friction resistance coefficient of the standard pipe section of each model is calculated using the formula, which is the unit friction resistance coefficient of each model. Then, the resistance reduction rate ξ of the tunnel model with different connecting flue spacing can be calculated. The local resistance coefficient and friction resistance coefficient can be obtained by the following formula:

[0041] In the formula: α - local resistance coefficient at each connecting flue; λ - friction resistance coefficient along each pipe section;

[0042] Where: λ, N·s 2 / m; ∆ - average wall roughness, referring to the "Detailed Rules for Ventilation Design of Highway Tunnels", the smoothness of the tunnel concrete wall is generally good, and the roughness is taken as 2.5mm; D - equivalent diameter of the tunnel section, m; The local drag coefficient α at each connecting flue is obtained according to the following Bernoulli equation:

[0043]

[0044]

[0045]

[0046] In the formula: α is the local resistance coefficient at the connecting flue, α AB α AC α AE The local drag coefficients P for sections AA to BB, AA to CC, and AA to EE are respectively. A P B P C P E These are the static pressures at sections AA, BB, CC, and EE, respectively, V. A V B V C V E These are the flue gas velocities at cross sections AA, BB, CC, and EE, respectively, and D. A D B D C D E These are the equivalent diameters of sections AA, BB, CC, and EE, respectively, which are the perimeters of the sections. A L B L C L E These are the distances between section AA and the nearest flue gas inlet on the flue gas inflow side, section BB and the nearest flue gas inlet on the flue gas inflow side, section EE and the nearest flue gas inlet on the flue gas inflow side, and the distance from section CC to the flue gas exhaust channel, λ. A , λ B , λ C , λ E They are the L-shaped driving tunnels. A Section, smoke exhaust duct L B Section, connecting flue Lc section, smoke exhaust duct L E The friction coefficient along the section. Section AA is the starting section where flue gas flows into the vehicular tunnel in the standard pipe section, and is equal to other sections of the vehicular tunnel. Sections BB and EE are the sections at both ends of the exhaust duct in the standard pipe section, and are equal to other sections of the exhaust duct. Section CC is the section at the flue gas outlet in the connecting flue, and is equal to other sections of the connecting flue.

[0047] S5: Compare the obtained data with three indicators in the performance-based evaluation model for connecting flue spacing to determine the rationality of the connecting flue spacing, including the flue gas spread range L. 60 The distance from the heat source to the smoke exhaust outlet should not exceed twice the distance between the heat source and the exhaust outlet; the smoke exhaust efficiency η should be greater than 95%; and the resistance reduction rate ξ should be greater than 5%. Figure 9 As shown in Table 3, among the four different tunnel models with varying spacing between connecting flues as defined in S4, those meeting the requirements are as follows. Table 3 Recommended parameter values ​​under different indicator criteria

[0048] As shown in the table, both J01 and J02 meet the three indicators in the performance-based evaluation model for the spacing optimization of connecting flues. Based on this, the friction resistance coefficients of the two working conditions are analyzed, and the working condition with the smaller friction resistance coefficient, namely the J01 working condition, is selected.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An optimized design method for the spacing of connecting flues in extra-long cross-sea highway tunnels, characterized in that, Includes the following steps: Step 1: Use ICEM CFD software to create multiple tunnel models with the same length and opening size. Each tunnel model includes two parallel vehicular tunnels designed according to the design parameters. Smoke exhaust ducts are set above the roof of the vehicular tunnels. Smoke exhaust outlets are arranged at equal intervals according to the design spacing on the roof of the vehicular tunnels. Different numbers of tunnel models are set with different numbers of vehicular cross passages in an increasing order. Adjacent vehicular cross passages are equidistant. A connecting smoke duct is set above each vehicular cross passage according to the design parameters. Tunnel models with different connecting smoke duct spacings are numbered and corresponding msh mesh files are generated. The number of vehicular cross passages of adjacent numbered tunnel models differs by n. Step 2: Import the msh mesh files with different numbers into Fluent software. Use Fluent software to set fire sources with the same power at the same location in different models. The smoke exhaust volume of the fire sources is the same. Open the same number of smoke exhaust ports in the upstream and downstream directions of the fire sources. Calculate the fire source model to simulate the spread of smoke in the driving tunnel and save it as dat data format with different numbers. Step 3: Import the .dat files with different numbers into the CFD-Post software. Use the CFD-Post software to uniformly set several points at the top of the tunnel of different models to extract temperature values, and set slices at the positions of the smoke exhaust vents of the tunnel of different models to extract smoke exhaust volume values. Set the width of the slices to be the same as that of the tunnel and the height of each slice to be the same. The temperature values are extracted from each point, and the distance L from the farthest point to the fire source in the tunnel model with different interpass distances is counted when the temperature exceeds 60°C 60i ; The amount of carbon monoxide generated from each slice is extracted, the ratio of the carbon monoxide absorption amount of each opened exhaust port to the carbon monoxide generation amount released by the fire is calculated, and the exhaust efficiency η of each opened exhaust port in the tunnel model with different interconnecting flue spacings is obtained i ; Step 4: Using CFD-Post software, set cross-sections for extracting static pressure and flue gas flow at the midpoint of the vehicle tunnel or exhaust duct between adjacent connecting flues in different models, and at the end face of the connecting flue. The cross-sections are the cross sections of the vehicle tunnel, exhaust duct, or connecting flue. Calculate the sum of the local resistance coefficient of the connecting flue and the friction resistance coefficient of the half-section smoke exhaust channels on both sides of the connecting flue in the tunnel model with different connecting flue spacing, that is, the unit friction resistance coefficient Δξ of the tunnel model with different connecting flue spacing. i ; Step 5, Select L 60i ≤2L, and η i ≥95% tunnel model, 2L is the length of the area covered by the set open smoke vent along the longitudinal direction of the tunnel; Step 6: Calculate the resistance reduction rate ξ for adjacent tunnel models, i.e., the friction resistance coefficient Δξ of the i-th tunnel model. i The frictional resistance coefficient Δξ of the (i+n)th tunnel model i+n The difference between Δξ and Δξ i If the ratio of ξ is not greater than 5%, then the tunnel model numbered i+n is removed. Step 7: Select the tunnel model with the lowest frictional resistance from the different tunnel models selected in Step 6 to obtain the optimal spacing for the connecting flue.

2. The method for optimizing the spacing of connecting flues in extra-long cross-sea highway tunnels according to claim 1, characterized in that, The local drag coefficient α is calculated as follows: α=αAB+αAC+αAE In the formula: α is the local resistance coefficient at the connecting flue, α AB α AC α AE The local drag coefficients P for sections AA to BB, AA to CC, and AA to EE are respectively. A P B P C P E These are the static pressures at sections AA, BB, CC, and EE, respectively, V. A V B V C V E These are the flue gas velocities at cross sections AA, BB, CC, and EE, respectively, and D. A D B D C D E These are the equivalent diameters of sections AA, BB, CC, and EE, respectively, which are the perimeters of the sections. A L B L C L E These are the distances between section AA and the nearest flue gas inlet on the flue gas inflow side, section BB and the nearest flue gas inlet on the flue gas inflow side, section EE and the nearest flue gas inlet on the flue gas inflow side, and the distance from section CC to the flue gas exhaust channel, λ. A , λ B , λ C , λ E They are respectively with L A Equal length vehicular tunnel section, and L B Equal length smoke exhaust duct section, connecting smoke duct section of equal length with Lc, and L E The friction coefficient of the smoke exhaust duct section of equal length, section AA is the end face of the driving tunnel section between adjacent connecting smoke ducts in the tunnel model that is close to the smoke inflow side, sections BB and EE are the end faces of the smoke exhaust duct above section AA that are close to section AA and the end faces that are far from section AA, and section CC is the end face of the smoke outflow end in the connecting smoke duct.

3. The method for optimizing the spacing of connecting flues in extra-long cross-sea highway tunnels according to claim 1, characterized in that, The friction factor λ is calculated as follows: Where: Δ—average wall roughness; D—equivalent diameter of tunnel cross section.

4. The method for optimizing the spacing of connecting flues in extra-long cross-sea highway tunnels according to claim 1, characterized in that, The fire source power is set at 50MW, and the smoke exhaust volume is 360m³. 3 / s.

5. The method for optimizing the spacing of connecting flues in extra-long cross-sea highway tunnels according to claim 1, characterized in that, The heat source is placed between at least two open smoke vents, and the number of open smoke vents is even.

6. The method for optimizing the spacing of connecting flues in extra-long cross-sea highway tunnels according to claim 5, characterized in that, In the worst-case scenario of a highway tunnel fire, the fire source is located in the middle of the highway tunnel section between adjacent connecting smoke ducts.

7. The method for optimizing the spacing of connecting flues in extra-long cross-sea highway tunnels according to claim 1, characterized in that, In Fluent software, the fire source was set as the mass-flow inlet, the tunnel wall was set as the wall boundary condition with a roughness of 2.5 mm, the SIMPLE pressure correlation algorithm was selected as the separate solver, the discretization scheme of the pressure in the simulation was set to body force weighted, the momentum, carbon dioxide and energy were calculated using the second-order upwind scheme, and the turbulent kinetic energy and turbulent dissipation rate were calculated using the first-order upwind scheme. The default values ​​of the relaxation factors for pressure, momentum, turbulent kinetic energy and turbulent dissipation rate were reduced to 0.3, 0.5, 0.5 and 0.5 respectively. The simulation calculation time was 1200 s and the model was run to simulate the spread of smoke in the driving tunnel.

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