Simulation method for explosion venting of square pipeline with lateral guide pipe

Abstract

The invention relates to the technical field of pipeline gas explosion venting, in particular to a simulation method for venting of a square pipeline with a lateral guide pipe. The method comprises the following steps: S1, establishing a pipeline model comprising a main pipeline and a plurality of lateral conduits, and establishing an external environment area in a preset range outside the pipeline model; s2, performing grid division on the pipeline model; s3, importing a grid file, and setting a basic model; s4, setting a component transportation model, boundary conditions, a pressure and speed coupling method, a discrete method and overpressure and temperature monitoring; s5, an ignition area is established, and design is initialized; and S6, iterative calculation is carried out, post-processing is carried out on a calculation result, explosion overpressure and flame wave characteristics are obtained, and a flow field flow trace is displayed. The method solves the problem that discharge safety is not considered in existing pipeline explosion venting, and a theoretical basis is provided for engineering protection measures.

Description

Technical Field

[0001] This invention relates to the field of pipeline gas explosion venting technology, specifically to a simulation method for venting a square pipeline with a lateral conduit. Background Technology

[0002] Combustible gas pipelines are highly susceptible to leaks due to various factors, and underground urban utility tunnels contain a dense network of gas pipelines connecting vital underground infrastructure. If a gas pipeline leaks and encounters an ignition source such as an electrostatic spark within the underground utility tunnel space, causing an explosion, the underground utility tunnel structure will be subsequently destroyed, resulting in incalculable loss of life and property.

[0003] In the field of explosion venting research, many scholars have analyzed the explosion of flammable gases in pipelines using experiments and computational fluid dynamics. However, many explosion venting methods only involve opening holes on the pipeline surface, without considering the safe release of gases during actual applications. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a numerical simulation method for explosion venting of a square pipe with a lateral conduit to solve the problem that the safety of venting is not considered in the existing pipe explosion venting, and to provide a theoretical basis for engineering protection measures.

[0005] The technical solution adopted by this invention to solve its technical problem is: a simulation method for explosion venting of a square pipe with a lateral conduit, comprising: Step S1: Establish a pipeline model including the main pipeline and several lateral conduits, and establish an external environment area with a preset range outside the pipeline model; Step S2: Mesh the pipeline model; Step S4: Import the mesh file and set up the basic model; Step S4: Set the component transport model, boundary conditions, pressure-velocity coupling method, discretization method, overpressure and temperature monitoring; Step S5: Establish the ignition zone and initialize the design; Step S6: Iterative calculation, post-processing of the calculation results to obtain the characteristics of explosion overpressure and flame wave, and to visualize the flow field trace.

[0006] Furthermore, in step S4, the component transport model is set up, specifically as follows: Open the component transport model, select the partially premixed combustion model, and set the turbulent flow flame velocity model to the Zimont equation model.

[0007] Furthermore, in step S4, setting the boundary conditions specifically involves: First, all surfaces are made into insulated, smooth walls. After starting the calculation, when the pressure in the main pipeline reaches the preset pressure, the corresponding positions on the right end of the main pipeline, the contact part between the main pipeline and the side conduit, and the upper side of the side conduit are set as pressure outlets according to the simulated working conditions.

[0008] Further, in step S4, the pressure-velocity coupling method is set to use the PISO method, and the discretization method adopts a second-order upwind scheme.

[0009] Furthermore, in step S4, overpressure and temperature monitoring are set up, specifically as follows: Monitoring points were set up to monitor explosion overpressure at the detection points, and temperature change cloud map monitoring was set up for the entire pipeline area.

[0010] Furthermore, in step S5, the ignition zone is established; specifically: An ignition zone is set at the center of the closed end on the left side of the main pipeline.

[0011] Furthermore, in step S6, the calculation results are post-processed to obtain the explosion overpressure and flame wave characteristics; specifically including: The files exported from Fluent were imported into Tecplot and Origin software for post-processing of the results. The propagation of explosion overpressure and flame temperature was observed, and pressure and temperature cloud maps at different times, as well as data monitored at monitoring points, were extracted.

[0012] By adopting the above technical solution, the present invention has the following beneficial effects: (1) This invention can simulate the explosion propagation process and the explosion relief process of mixed gas in a pipeline containing a lateral conduit, obtain the explosion overpressure and flame propagation characteristic values, and analyze its explosion relief law; the research results provide a theoretical basis for engineering protection measures (such as the optimization of the size and location of the explosion relief conduit), reduce the losses caused by gas leakage accidents in urban underground pipe corridors, and protect the life and property safety of ground personnel; (2) The simulation method in this invention is suitable for pipeline explosion relief conditions containing lateral conduits of different sizes and positions. The model size and distribution position can be flexibly adjusted according to the simulation scheme settings to accurately simulate the explosion relief process inside the pipeline.

[0013] (3) Compared with conducting large-scale underground pipe gallery gas explosion experiments, the present invention uses numerical simulation to study the propagation characteristics of gas explosions. It has the advantages of low cost, flexible operation, comprehensive analysis and short research cycle. It can quantitatively describe the important parameters in the explosion relief process, and then analyze the nature of the accident, so that the results have universal physical significance. Attached Figure Description

[0014] Figure 1 This is a flowchart of a simulation method for venting an explosion in a square pipe with a lateral conduit, according to the present invention. Figure 2 This is a schematic diagram of a pipe with a lateral conduit according to the present invention; Figure 3 This is a diagram of the experimental apparatus for a pipe with a lateral conduit according to the present invention; Figure 4 This is a schematic diagram of the mesh division of the present invention; Figure 5 This is a schematic diagram of the explosion overpressure curve inside the pipeline according to the present invention; Figure 6 This is a diagram showing flame propagation without lateral conduit. Figure 7 This is a diagram showing the flame propagation in lateral duct No. 1. Figure 8 This is a diagram showing the flame propagation in lateral duct No. 2. Figure 9 This is a diagram showing the flame propagation in lateral duct No. 3. Detailed Implementation

[0015] like Figure 1 As shown, a simulation method for venting a square pipe with a lateral conduit includes: (1) Establish a physical model with the same dimensions as the experimental pipe: A two-dimensional pipe model with the same dimensions as the experimental pipe was created using SpceClaim software. The experimental pipe is as follows: Figure 2 As shown in the figure, the model consists of two regions: a lateral conduit and a main pipe. The main pipe is 2000mm long and 150mm wide. Lateral conduits, 60mm wide and 80mm high, are set at distances of 300mm, 1000mm, and 1700mm from the left end of the main pipe, respectively, and are designated as lateral conduit 1, lateral conduit 2, and lateral conduit 3. An external environment region is established outside the pipe model, with the overall calculation area measuring 2300mm long and 1800mm wide.

[0016] (2) Mesh the established model:

[0017] Import the completed model into Ansys Meshing software. Name the geometry: the left end of the main pipe is closed, the right end is open, the junction of the main pipe and the side duct, and the upper end of the side duct are all open. The ignition end is located at the center of the left end. The pipe mesh size is 2mm, and the external environment mesh size is 4mm. Export the MESH mesh file. A schematic diagram of the mesh generation is shown below. Figure 4 As shown.

[0018] (3) Import the mesh file and set up the basic model: Import the mesh file into Fluent, check and adjust the model size and units, select transient pressure basis solution, enable the energy equation, and select the standard two-equation k-ε model as the turbulence model.

[0019] (4) Setting up the component transport model: Open the component transport model, select the partially premixed combustion model, the turbulent flow flame velocity model is the Zimont equation model, select the equilibrium state bifunctional PDF lookup table that considers the effects of inlet diffusion and compression, and select the mass fraction of CH4 as 1, the mass fraction of O2 as 0.78, and the mass fraction of N2 as 0.22.

[0020] (5) Set boundary conditions: First, set all surfaces as insulated smooth walls. After starting the calculation, when the pressure inside the pipe reaches the preset pressure (which can be 2000Pa, depending on the actual situation), set the corresponding positions at the right end of the main pipe, the contact part between the main pipe and the side conduit, and the upper side of the side conduit as pressure outlets according to the simulated working conditions, which is consistent with the actual experimental conditions.

[0021] In the simulation of the working condition without explosion relief duct, only the right end of the main pipeline is used as the pressure outlet; in the simulation of the No. 1, No. 2 or No. 3 lateral ducts, only the contact part between the corresponding lateral duct and the main pipeline, the upper end of the corresponding lateral duct and the right end of the main pipeline are used as the pressure outlet.

[0022] Specifically, setting a pressure threshold to initiate explosion venting is more in line with actual working conditions. Traditional explosion venting methods often assume that the vent is always closed, while this method sets a pressure threshold based on actual experimental conditions to initiate explosion venting, thereby improving the accuracy of the simulation and further optimizing the explosion venting effect.

[0023] (6) Set the algorithm: The pressure-velocity coupling method uses the PISO method, and the discretization method uses the second-order upwind scheme.

[0024] (7) Set up overpressure and temperature monitoring: Based on the location of the experimental pressure sensor, the monitoring point is used to monitor the explosion overpressure, and the temperature change cloud map is set to monitor the overall pipeline area.

[0025] (8) Set the ignition zone: A semi-circular ignition area with a radius of 4mm is set at the center of the left closed end.

[0026] (9) Initialization design: The initial pressure is set to 101325 Pa, the initial temperature to 298.15 K, the initial process variable to 0, and the mixture fraction to 0.055. Ignition is performed using PATCH with the process variable of the semi-circular ignition zone set to 0.1.

[0027] (10) Iterative calculation; The iteration time step is set to 0.001s, and the number of iterations is 300.

[0028] (11) Post-processing of calculation results The files exported from Fluent were imported into Tecplot and Origin software for post-processing of the results. The propagation of explosion overpressure and flame temperature was observed, pressure and temperature cloud maps at different times were extracted, as well as data monitored at monitoring points, and the flow field traces were visualized.

[0029] The above simulation method was used to simulate the following conditions: no explosion venting duct, only lateral duct No. 1 as the explosion venting duct, only lateral duct No. 2 as the explosion venting duct, and only lateral duct No. 3 as the explosion venting duct. Figure 6 This is a diagram showing flame propagation without lateral conduit. Figure 7 , Figure 8 and Figure 9 The images show the flame propagation diagrams for lateral ducts 1, 2, and 3, respectively. Figure 5 This is a schematic diagram of the overpressure curves inside the pipelines during the explosion of lateral conduits No. 1, 2, and 3.

[0030] (12) Network independence verification Meshing was used to divide the model into meshes of different sizes: 0.5mm, 1mm, 2mm, and 4mm. Fluent was then used for iterative calculations, and a reasonable mesh size was selected based on the calculation results.

[0031] Specifically, the inventors of this invention considered that in order to install explosion relief outlets in underground utility tunnels, it is necessary to take into account the certain distance between the utility tunnel and the ground. Therefore, explosion relief conduits (lateral conduits) can be installed at the weak points of the utility tunnel. The release of the explosion relief conduits reduces the explosion pressure and releases the explosion products or unburned mixtures to a designated safe area, which can greatly protect the safety of ground personnel and buildings.

[0032] Based on this, this embodiment conducts a numerical simulation of the propagation process of a mixed gas explosion in the case of a pipeline explosion with lateral conduits. By analyzing the flame release range and flame jet height in the environment, it is possible to understand the hazards that the explosion may cause when released into the environment. It is proposed to set up multiple lateral conduits at specific locations in the pipeline (such as 300mm, 1000mm, and 1700mm from the left end).

[0033] Through simulation analysis of different conduits, it was found that in the case of a conduit without explosion venting (i.e., a lateral conduit), the explosion venting time is 169 ms, and the flame vents from the end of the conduit. Specifically, as shown below... Figure 6As shown. When only lateral duct No. 1 is venting, the flame reaches lateral duct No. 1 in 38ms and begins to vent from lateral duct No. 1. The flame finally reaches the terminal vent in 320ms, as detailed below. Figure 7 As shown; when only lateral duct No. 2 is venting, the flame reaches lateral duct No. 2 in 85ms and begins to vent from lateral duct No. 2. The flame finally reaches the terminal vent in 230ms, as detailed below. Figure 8 As shown; when only the No. 3 lateral duct is venting, the flame reaches the No. 3 lateral duct in about 145ms, and venting begins from the No. 3 lateral duct. The flame finally reaches the terminal explosion vent in 181ms, as detailed below. Figure 9 As shown in the diagram, the flame propagation speed diagram reveals that the closer the ignition point is to the lateral duct, the earlier the flame begins to vent, the longer it takes for the flame to reach the final explosion vent, and the better the venting effect.

[0034] The results showed that the No. 1 lateral conduit (closest to the ignition end) had the best effect on overpressure relief and flame suppression. By extending the lateral conduit to directionally release the explosion products to a safe area (such as the air), the safety of personnel and buildings on the ground can be protected. This allows for preventative measures and helps to prevent pipeline gas explosion accidents, reduce losses caused by gas explosions, and facilitate the directional release of the explosion. Furthermore, this implementation was based on actual experimental conditions (where the experimental setup is as follows...). Figure 3 As shown, the pipeline consists of three sections of acrylic square tubing connected by flanges and bolts: a 500mm front section, a 1000mm middle section, and a 500mm rear section, for a total length of 2000mm. The cross-sectional dimensions are 150mm x 150mm, and the pipe wall thickness is 20mm. The left end of the main pipeline is the ignition end, sealed with an acrylic plate containing an air inlet and ignition point. The right end is the explosion vent end, sealed with PVC film. An overpressure sensor is installed 200mm from the end of the vent, connected to an overpressure sensor. Although... Figure 3 The diagram illustrates three lateral conduits, but only one lateral conduit is installed at a time. For example, when installing the No. 1 explosion vent conduit, only one lateral conduit is installed on the entire main pipe at a distance of 300mm from the left end of the main pipe. The junction of the lateral conduit and the main pipe's explosion vent, as well as the upper side of the lateral conduit, are sealed with PVC film. This reveals the correspondence between the data required for numerical simulation and actual experimental conditions. The film opening ratio is set according to different cases, based on statistical analysis of experimental data, and conforms to actual conditions.

[0035] The analysis of flame propagation during an explosion primarily utilizes Tecplot to display flame cloud maps. Fluent and post-processing software are employed to quantitatively analyze parameters such as the deformation of the flame front inside and outside the pipe and duct, the propagation velocity of the flame front, and temperature changes in the flame cloud map. This analysis is combined with explosion overpressure curves for comprehensive analysis. Furthermore, the software is used to analyze the flow field traces of flame propagation inside and outside the pipe, revealing the influence of airflow on the external environment after a methane explosion. This allows for a more microscopic analysis of the venting process inside and outside the pipe. The post-processing software visualizes the flow field traces outside the pipe, analyzing the flow field changes that occur during flame propagation after a pipe explosion. This provides guidance for comprehensive analysis of pipe explosions in real-world scenarios. Building upon traditional numerical simulation analysis, this patent imports the results from Fluent simulations into Tecplot software, using the software to visualize the flow field traces and analyze the flow field during a methane explosion in a pipe. Based on the analysis of the flow field traces during a methane explosion in a pipeline, it was also discovered that the vortices formed by the flow field traces near the duct outside the pipeline undergo a certain degree of stretching deformation according to changes in simulation conditions. Traditional numerical simulations mainly focus on the flow field changes within the pipeline, while this study found that the vortices outside the No. 3 lateral duct exhibit greater stretching deformation. Combining the above analysis, it can be concluded that, considering the venting situation of the three ducts in this embodiment, the No. 1 lateral duct is more conducive to the venting of overpressure and the suppression of flame propagation, thus facilitating venting. Furthermore, it can be determined that the flame venting height in the three lateral duct environments can reach 0.65m, but the ambient temperature outside the duct located further forward is higher. Moreover, the flame outside the pipeline perfectly matches the experimental conditions, proving the feasibility of the simulation method in this embodiment. For scenarios such as urban underground utility tunnels, a design scheme for reducing explosion hazards through lateral duct venting is proposed, providing a theoretical basis for engineering protection measures (such as optimization of venting duct size and location). Analysis of the changes in the external airflow field traces after the explosion venting guides the delineation of safe zones and the formulation of protection strategies.

[0036] Therefore, in practical applications, if a pipe gallery or other similar structure is about to explode or has already exploded, the explosion will be released to the maximum extent through the nearest conduit. Since the flames released into the environment are at a high height, the method of extending the explosion vent conduit can be adopted. The specific size can be determined according to the simulation situation to release the hazards generated by the explosion into the air, so as to protect people on the ground from the effects of high temperature flames and shock waves.

[0037] In this embodiment, the following assumptions are made regarding the simulation process to facilitate numerical calculation: A. Pipeline explosion relief system, without considering the influence of natural airflow or obstacles; B. The explosion source gas is a mixture of methane and air, where both methane and air are considered ideal gases and follow the ideal gas law. The explosion reaction occurs under normal temperature and pressure conditions. C. Apart from the ignition source of the methane / air mixture explosion, there are no other heat sources in the pipeline; D. The pipe wall is a rigid, smooth wall.

[0038] In addition to considering the mass conservation equation, energy conservation equation, momentum conservation equation, and chemical composition balance equation, the gas state equation and turbulence equation must also be taken into account during the explosion process of combustible gases in the pipeline. These equations are all set within the software.

[0039] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1.A simulation method for explosion venting of square pipe with lateral ducts, comprising: S1, establishing a pipe model comprising a main pipe and several lateral ducts, and establishing an external environment area of a preset range outside the pipe model; S2, meshing the pipe model; S3, importing the mesh file and setting a basic model; S4, setting a component transport model, boundary conditions, pressure-velocity coupling method, discrete method, overpressure and temperature monitoring; S5, establishing an ignition area and initializing a design; S6, iterative calculation, post-processing the calculation results, obtaining explosion overpressure and flame wave characteristics, and visualizing flow field flow traces. 2.The simulation method for explosion venting of square pipe with lateral ducts according to claim 1, wherein in S4, the component transport model is set as follows: opening the component transport model, selecting a partial premixed combustion model, and setting the turbulent flow flame speed model as the Zimont equation model. 3.The simulation method for explosion venting of square pipe with lateral ducts according to claim 1, wherein in S4, the boundary conditions are set as follows: initially, all surfaces are adiabatic smooth walls, and after starting the calculation, when the pressure in the main pipe reaches a preset pressure, the right end of the main pipe, the contact part between the main pipe and the lateral duct, and the corresponding positions on the upper side of the lateral duct are set as pressure outlets according to the simulation working condition. 4.The simulation method for explosion venting of square pipe with lateral ducts according to claim 1, wherein in S4, the pressure-velocity coupling method is set as the PISO method, and the discrete method is set as the second-order upwind scheme. 5.The simulation method for explosion venting of square pipe with lateral ducts according to claim 1, wherein in S4, the overpressure and temperature monitoring are set as follows: setting monitoring points, monitoring explosion overpressure at the monitoring points, and monitoring temperature change cloud map changes in the whole pipe area. 6.The simulation method for explosion venting of square pipe with lateral ducts according to claim 5, wherein in S5, the ignition area is established as follows: setting the ignition area at the center of the closed end of the left end of the main pipe. 7.The simulation method for explosion venting of square pipe with lateral ducts according to claim 1, wherein in S6, the calculation results are post-processed to obtain explosion overpressure and flame wave characteristics, and the post-processing specifically comprises: importing the Fluent-derived file into Tecplot and origin software for result post-processing, checking the propagation of explosion overpressure and flame temperature, extracting pressure and temperature cloud maps at different times, and monitoring data of the monitoring points. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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