Method for evaluating smoke blocking performance of bifurcated tunnel air curtain

Abstract

The application discloses a kind of bifurcated tunnel air curtain smoke resistance performance evaluation method, belong to the ventilation and fire prevention and control design field of bifurcated tunnel.This application method: the bifurcated tunnel model is established;Adopt CFD-DEM coupling simulation method;Numerical model is established and set;Parameter is calibrated;Setting working condition;CFD-DEM model coupling calculation;Evaluate air curtain smoke resistance performance.The application can systematically evaluate the smoke resistance performance of air curtain in bifurcated tunnel by establishing CFD-DEM coupling model;By running CFD-DEM coupling solution program, the motion trajectory and force condition of dust particles under the action of air curtain can be obtained;By changing the parameters of longitudinal ventilation-air curtain ventilation system in main tunnel, such as air curtain injection angle, injection speed, thickness and longitudinal wind speed in main tunnel, the dust removal effect under different working conditions can be analyzed;Based on simulation results, the design and parameter adjustment of air curtain can be optimized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of ventilation and fire prevention and control design of branched tunnels, and particularly relates to a method for evaluating the smoke blocking performance of an air curtain in a branched tunnel. BACKGROUND

[0002] In urban traffic networks, branched tunnels pose challenges to smoke control under ventilation and fire conditions due to their special structural form. For tunnels with branches, not only the smoke spread in the main tunnel but also the safety in the branch tunnels should be considered, and it is necessary to avoid smoke entering the branch tunnels as much as possible, otherwise personnel escaping will pass through the smoke dense area, which will easily cause casualties.

[0003] Air curtain dust removal technology in branched tunnels is an effective solution, but how to evaluate its performance is still a problem. Existing technologies mainly focus on the top smoke exhaust-air curtain system of a single tunnel, and the research on the longitudinal ventilation-air curtain system of branched tunnels is relatively less. This leads to many uncertainties in how to effectively control the diffusion and discharge of smoke in branched tunnels, especially under fire conditions. SUMMARY

[0004] The purpose of the present application is to provide a method for evaluating the smoke blocking performance of an air curtain in a branched tunnel, which aims to systematically evaluate the smoke blocking performance of an air curtain in a branched tunnel and provide a theoretical basis and guidance for practical engineering applications.

[0005] The technical solution of the present application is: a method for evaluating the smoke blocking performance of an air curtain in a branched tunnel, comprising the following steps:

[0006] S1, establishing a branched tunnel model: establishing a tunnel model, taking a certain length of the main tunnel and the ramp before and after the branch as the calculation domain;

[0007] S2, setting a numerical simulation method: adopting a CFD-DEM coupling simulation method, CFD is used for numerical simulation of air flow field, and DEM is used for numerical simulation of smoke particles;

[0008] S3, establishing and setting a numerical model: based on DEM, setting particle factory, including: number of particles generated per second, particle size distribution, basic particle size; based on DEM, setting smoke particle parameters, including: particle temperature, particle thermal conductivity, microscopic parameters of particle and plane contact model, microscopic parameters of particle and particle contact, particle size distribution; based on CFD, setting fire scene, including: fire source material, fire source volume, fire source heat release rate, air curtain injection angle, air curtain injection speed, air curtain thickness, main tunnel longitudinal wind speed;

[0009] S4, calibration parameters: perform material combustion test, collect and measure the smoke temperature of the particle material obtained after the same fire source material is burned; DEM numerical simulation of the drum experiment is carried out through the discrete element method to obtain DEM particle-plane contact parameters; DEM numerical simulation of the repose angle test is carried out through the discrete element method to obtain DEM particle-particle contact parameters; then, a fire scale experiment is carried out, CFD numerical simulation of the fire scale experiment is carried out through the computational fluid dynamics method, the smoke temperature, DEM particle-plane contact parameters and DEM particle-particle contact parameters obtained through the above tests are compared with the results of CFD numerical simulation respectively, and the smoke temperature, DEM particle-plane contact parameters and DEM particle-particle contact parameters are adjusted and calibrated;

[0010] S5, setting working conditions: selecting air curtain parameters, including air curtain thickness, jet velocity and jet angle, setting multiple cross working conditions according to parameters and the number of data corresponding to each parameter, comprehensively reflecting the influence of air curtain parameter change on smoke blocking effect;

[0011] S6, running the solving program and outputting the result data: CFD-DEM model coupling calculation, obtaining particle motion trajectory and force size based on DEM calculation result, obtaining air flow field distribution based on CFD calculation result;

[0012] S7, evaluating the smoke blocking performance of the air curtain: obtaining the motion form of smoke particles under the joint action of the main tunnel longitudinal wind and the air curtain jet air based on the particle motion trajectory and the force size, analyzing the motion law of the smoke particles at the ramp; analyzing the influence of the particles on the fluid based on the distribution of different physical quantities of the air flow field; evaluating the smoke blocking performance of the air curtain by analyzing the interaction between the smoke particles and the air at the ramp.

[0013] As a further improvement of the application, in step S2, when performing numerical simulation of the air flow field, the fluid phase (air) control equation is established based on the CFD method, and the fluid phase control equation includes a continuity equation and a momentum equation;

[0014] The continuity equation is represented as:

[0015]

[0016] Wherein, ρf is the air density, u is the average velocity of the gas, ε is the gas void ratio, represents the gradient;

[0017] The momentum equation is represented as:

[0018]

[0019] Wherein, p is the fluid pressure, F f-p is the interaction force between air and particles, τ is the gas stress tensor, and g is the gravitational acceleration.

[0020] As a further improvement of the present application, in step S2, when the smoke particle numerical simulation is carried out, the solid phase (smoke particle) motion control equation is established according to the DEM method, and the solid phase control equation includes a particle translational equation and a particle rotational equation.

[0021] The particle translational equation is expressed as:

[0022]

[0023] Wherein, m i is the mass of particle i, v i is the horizontal velocity of particle i, f c，ij is the contact force between particles, f d，ij is the viscous resistance between particles, f p-f，i is the force of particle i and air fluid;

[0024] The particle rotational equation is expressed as:

[0025]

[0026] Wherein, ω i is the angular velocity of particle i, T ij is the tangential force moment between particles, M ij is the rolling friction moment between particles, I i is the particle rotational inertia.

[0027] The interaction force of air and particles exists in the established fluid phase control equation and solid phase control equation, and the DEM and CFD methods can be coupled and calculated through the interaction force.

[0028] As a further improvement of the present application, in step S3, when the particle factory is set based on DEM, the particle factory geometric characteristics are set as a surface area, which is attached to the upper part of the tunnel inner wall and flows towards the branch opening under the driving of the longitudinal wind. Due to the small density, the upper part of the tunnel inner wall is attached to move, which simulates the flow condition of real smoke.

[0029] As a further improvement of the present application, in step S3, when the smoke particle parameters are set based on DEM, the particle temperature is directly calibrated by the test, and the particle gradation, the particle thermal conductivity, the microscopic parameters of the particle and plane contact model, and the microscopic parameters of the particle and particle contact are calibrated by combining the test and numerical simulation.

[0030] As a further improvement of the present application, in step S3, the boundary condition is set as: the corresponding plane of the tunnel inlet and outlet is a default pressure outlet.

[0031] The present application has the following beneficial effects:

[0032] 1. Evaluate the smoke blocking performance of air curtains in branched tunnels: By establishing a CFD-DEM coupled model, the smoke blocking performance of air curtains in branched tunnels can be systematically evaluated. This model takes into account the interaction of air flow field, dust particle distribution and air curtain, and can provide more accurate and comprehensive evaluation results.

[0033] 2. Quantitative analysis of the motion trajectory and force condition of dust particles: By running the CFD-DEM coupled solution program, the motion trajectory and force condition of dust particles under the action of air curtain can be obtained. This helps to understand the distribution and migration law of particles in the tunnel, and provides basis for optimizing the design and parameter adjustment of air curtain.

[0034] 3. Evaluate the smoke blocking effect under different working conditions: By changing the parameters of the longitudinal ventilation-air curtain ventilation system in the main tunnel, such as the air curtain injection angle, injection speed, thickness and longitudinal wind speed in the main tunnel, the dust removal effect under different working conditions can be analyzed. This helps to find the optimal design scheme and improve the dust removal efficiency of air curtain.

[0035] 4. Optimize the design and parameter adjustment of air curtain: Based on the simulation results, the design and parameter adjustment of air curtain can be optimized. For example, by analyzing the motion trajectory and force condition of particles, the angle, speed and thickness of air curtain can be adjusted to better control the diffusion and emission of dust particles. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is the fire working condition diagram of branched tunnel;

[0037] Figure 2 is the velocity flow field diagram of tunnel branch;

[0038] Figure 3 is the velocity flow field vector diagram of tunnel branch.

[0039] In the figure, 1 is the main tunnel; 2 is the ramp; 3 is the air curtain; 4 is the fire source; 5 is the longitudinal wind. DETAILED DESCRIPTION

[0040] The present application will be further described in detail below in combination with the drawings.

[0041] Example 1,

[0042] The fire working condition is as Figure 1 shown, the air curtain 3 is arranged at the branch of the main tunnel 1 and the ramp 2, and the fire source 4 is arranged in the direction of the longitudinal wind 5 of the main tunnel 1.

[0043] An evaluation method for the smoke blocking performance of air curtains in branched tunnels, characterized in that it comprises the following steps:

[0044] S1, establish a diverging tunnel model: establish a tunnel model, take the main tunnel and ramp of a certain distance length before and after the diverging section as the calculation domain. In order to shorten the numerical simulation time, the inner contour of the tunnel section is unchanged during modeling, and the outer contour of the tunnel section is set as a simple geometric shape, for example: rectangle.

[0045] S2, set the numerical simulation method: adopt the CFD-DEM coupling simulation method, CFD is used to carry out air flow field numerical simulation, and DEM is used to carry out smoke particle numerical simulation.

[0046] (1) When carrying out air flow field numerical simulation, the fluid phase (air) control equation is established based on CFD method, and the fluid phase control equation includes continuity equation and momentum equation;

[0047] The continuity equation is represented as:

[0048]

[0049] Wherein, ρf is the air density, u is the average velocity of gas, ε is the gas void ratio, represents the gradient;

[0050] The momentum equation is represented as:

[0051]

[0052] Wherein, p is the fluid pressure, F f-p is the interaction force between air and particles, τ is the gas stress tensor, and g is the gravity acceleration.

[0053] (2) When carrying out smoke particle numerical simulation, the solid phase (smoke particle) motion control equation is established according to DEM method, and the solid phase control equation includes particle translational equation and particle rotational equation;

[0054] The particle translational equation is represented as:

[0055]

[0056] Wherein, m i is the mass of particle i, v i is the horizontal velocity of particle i, f c，ij is the contact force between particles, f d，ij is the viscous resistance between particles, and f p-f，i is the force of particle i and air flow;

[0057] The particle rotational equation is represented as:

[0058]

[0059] Wherein, ω i is the angular velocity of particle i, and Tij M is the tangential force moment between particles ij I is the rolling friction moment between particles i I is the rolling friction moment between particles

[0060] The interaction force between air and particles exists in the established fluid phase control equation and solid phase control equation, and the two methods of DEM and CFD can be coupled and calculated through the interaction force.

[0061] S3, establishing and setting a numerical model:

[0062] (1) Based on DEM, the particle factory is set, including: the number of particles generated per second, particle size distribution, and basic particle size; the geometric characteristics of the particle factory are set as a surface area and attached to the upper part of the tunnel inner wall, and flow towards the branch under the driving of the longitudinal wind, and due to the small density, move along the upper part of the tunnel inner wall, simulating the flow of real flue gas.

[0063] (2) Based on DEM, the particle parameter setting is completed, including: particle temperature, particle thermal conductivity, microscopic parameters of particle and plane contact model, microscopic parameters of particle and particle contact, and particle size distribution; wherein the particle temperature is directly calibrated by test, and the particle size distribution, particle thermal conductivity, microscopic parameters of particle and plane contact model, and microscopic parameters of particle and particle contact are calibrated by test and numerical simulation.

[0064] (3) Based on CFD, the setting of fire scene is completed, including: fire source material, fire source volume, fire source heat release rate, air curtain injection angle, air curtain injection speed, air curtain thickness, and main tunnel longitudinal wind speed;

[0065] (4) The boundary condition is set as: the corresponding plane of the tunnel inlet and outlet is the default pressure outlet.

[0066] S4, parameter calibration: perform material combustion test, collect and measure the particle material obtained after the same fire source material is burned; perform DEM numerical simulation of drum test by discrete element method to obtain DEM particle-plane contact parameters; perform DEM numerical simulation of repose angle test by discrete element method to obtain DEM particle-particle contact parameters; then perform fire scale experiment, perform CFD numerical simulation of fire scale experiment by computational fluid dynamics method, compare the flue gas temperature, DEM particle-plane contact parameters, and DEM particle-particle contact parameters obtained by the above tests with the results of CFD numerical simulation, and adjust and calibrate the flue gas temperature, DEM particle-plane contact parameters, and DEM particle-particle contact parameters.

[0067] S5. Setting Operating Conditions: Select air curtain parameters, including air curtain thickness, jet velocity, and jet angle. Consider the actual range of parameter values, determine the data for each set of parameters, and set multiple sets of cross-operating conditions based on the parameters and the number of data corresponding to each parameter to comprehensively reflect the impact of changes in air curtain parameters on the smoke blocking effect.

[0068] S6. Run the solver and output the results data: CFD-DEM model coupled calculation, based on the DEM calculation results, the particle motion trajectory and force magnitude are obtained, and based on the CFD calculation results, the air flow field distribution is obtained.

[0069] S7. Evaluate the smoke-blocking performance of the air curtain: Based on the particle trajectory and the magnitude of the force, the motion pattern of smoke particles under the combined action of longitudinal wind in the main tunnel and air jet from the air curtain is obtained. The motion law at the ramp is analyzed. Smoke particles exhibit random motion at the bifurcation point, but overall, they still show a pattern of entering and leaving the ramp. The influence of particles on the fluid is analyzed based on the distribution of different physical quantities in the airflow field; such as... Figure 2 As shown, the jet of the air curtain is discharged from the vent at a certain speed. Although this part of the gas does not completely contact the ground and the ramp, the jet continuously entrains the surrounding air and smoke, and exchanges heat with the surrounding gas. Below it, a lower-velocity airflow field connects the airflow blown out from above, forming a continuous curtain-like airflow. Because this mixed airflow is very similar to the curtain-like airflow formed by a conventional air curtain, it is called an "equivalent air curtain." Figure 3 It can be seen that a vortex forms on the right side of the equivalent air curtain. Since the longitudinal wind in the main tunnel affects the airflow ejected from the air curtain at the bifurcation, the longitudinal wind in the main tunnel and the wind blowing perpendicularly from the air curtain in different directions are vector-superimposed, forming a vortex under their combined effect. By analyzing the interaction between smoke particles and air at the ramp entrance, the smoke-blocking performance of the air curtain is evaluated. The flow field distribution of the longitudinal wind-air curtain system at the bifurcation is already very complex. In addition, the disturbance caused by many tiny particles generated by the fire smoke at the bifurcation makes the performance evaluation of the air curtain even more difficult. Through the above analysis of motion laws and the influence of particles on fluids, the overall flow field at the bifurcation presents an "equivalent air curtain" state. Under the action of this flow field, although the particles move randomly, they still exhibit an overall pattern of being entrained and ejected from the ramp. By changing the operating parameters, the relative magnitudes of the entrainment and ejection capabilities are altered, leading to changes in the length of smoke propagation on the ramp, thus exploring the smoke-blocking performance of the air curtain.

[0070] The present application is based on the complexity of the longitudinal wind-air curtain ventilation system and the complexity of the flow field at the tunnel branch, establishes a CFD-DEM coupling model, adopts the coupling simulation technology of CFD and DEM, can comprehensively consider the distribution and movement of air flow field and dust particles, and provides more accurate simulation results. Through the model, the interaction of the air curtain and the flow field in the tunnel and the movement trajectory of the dust particles under the action of the air curtain can be simulated. The present application can systematically evaluate the air curtain dust removal performance in the branched tunnel through the CFD-DEM coupling technology, and can be widely applied to the ventilation and fire prevention and control design field of the branched tunnel. This method can not only be used for evaluating the performance of the existing branched tunnel, but also can provide guidance for the newly designed branched tunnel.

[0071] The evaluation method of the present application can be extended to other similar structures and systems, such as large underground interlinked tunnels, highway cross tunnels, etc., for scenes that need to control dust or smoke diffusion.

Claims

1. A method for evaluating the smoke-blocking performance of an air curtain in a bifurcated tunnel, characterized in that: Includes the following steps: S1. Establish the bifurcation tunnel model: Establish the tunnel model, taking the main tunnel and ramps with a certain distance before and after the bifurcation as the calculation domain; S2. Set the numerical simulation method: adopt the CFD-DEM coupled simulation method, where CFD is used for numerical simulation of air flow field and DEM is used for numerical simulation of smoke particles. S3. Establish and set up the numerical model: Based on the DEM, complete the setup of the pellet plant, including: the number of pellets generated per second, particle size distribution, and basic particle size; based on the DEM, complete the setting of smoke particle parameters, including: particle temperature, particle thermal conductivity, micro-parameters of the particle-plane contact model, micro-parameters of particle-particle contact, and particle size distribution; based on CFD, complete the setup of the fire scene, including: ignition source material, ignition source volume, ignition source heat release rate, air curtain injection angle, air curtain injection speed, air curtain thickness, and longitudinal wind speed of the main tunnel. S4. Calibration Parameters: Conduct material combustion tests, collect the particulate material obtained after burning the same ignition source material and measure the flue gas temperature; perform DEM numerical simulation of the drum test using the discrete element method to obtain the DEM particle-plane contact parameters; perform DEM numerical simulation of the angle of repose test using the discrete element method to obtain the DEM particle-particle contact parameters; then conduct fire scale tests, perform CFD numerical simulation of the fire scale test using computational fluid dynamics methods, compare the flue gas temperature, DEM particle-plane contact parameters, and DEM particle-particle contact parameters obtained from the above tests with the CFD numerical simulation results, and adjust and calibrate the flue gas temperature, DEM particle-plane contact parameters, and DEM particle-particle contact parameters accordingly. S5. Set working conditions: Select air curtain parameters, including air curtain thickness, jet velocity, and jet angle. Set multiple sets of cross working conditions according to the parameters and the number of data corresponding to each parameter to fully reflect the impact of changes in air curtain parameters on the smoke blocking effect. S6. Run the solver and output the results data: CFD-DEM model coupled calculation, based on the DEM calculation results, the particle motion trajectory and force magnitude are obtained, and based on the CFD calculation results, the air flow field distribution is obtained. S7. Evaluate the smoke-blocking performance of the air curtain: Based on the particle motion trajectory and the magnitude of the force, obtain the motion pattern of the smoke particles under the combined action of the longitudinal wind in the main tunnel and the air jet of the air curtain, and analyze their motion law at the ramp; analyze the influence of particles on the fluid based on the distribution of different physical quantities in the air flow field; evaluate the smoke-blocking performance of the air curtain by analyzing the interaction between smoke particles and air at the ramp entrance.

2. The method for evaluating the smoke-blocking performance of an air curtain in a bifurcation tunnel according to claim 1, characterized in that: In step S2, when performing numerical simulation of the air flow field, the fluid phase control equation is established based on the CFD method. The fluid phase control equation includes the continuity equation and the momentum equation. The continuity equation is expressed as: Where, ρ f Let ρ be the air density, u be the average gas velocity, and ε be the gas porosity. Represents the gradient; The momentum equation is expressed as: Where p is the fluid pressure, F f-p Let τ be the interaction force between air and particles, τ be the gas stress tensor, and g be the gravitational acceleration.

3. The method for evaluating the smoke-blocking performance of an air curtain in a bifurcation tunnel according to claim 1, characterized in that: In step S3, when setting up the pellet plant based on the DEM, the geometric features of the pellet plant are set as a surface region, attached to the upper part of the tunnel wall, and flow towards the bifurcation under the drive of the longitudinal wind. Due to its low density, it moves along the upper part of the tunnel wall, simulating the flow of real flue gas.

4. A method for evaluating the smoke-blocking performance of an air curtain in a bifurcation tunnel according to claim 1 or 3, characterized in that: In step S3, when setting the parameters of smoke particles based on DEM, the particle temperature is directly calibrated by experiment, while the particle size distribution, particle thermal conductivity, micro-parameters of the particle-plane contact model, and micro-parameters of particle-particle contact are calibrated by a combination of experiment and numerical simulation.

5. A method for evaluating the smoke-blocking performance of an air curtain in a bifurcation tunnel according to claim 1 or 3, characterized in that: In step S3, the boundary conditions are set as follows: the planes corresponding to the tunnel inlet and outlet are the default pressure outlets.

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