Method for evaluating smoke blocking performance of air curtain of bifurcated tunnel

Abstract

The invention discloses a method for evaluating smoke blocking performance of an air curtain of a bifurcated tunnel, and belongs to the field of ventilation and fire prevention and control design of the bifurcated tunnel. The method comprises the following steps: establishing a bifurcated tunnel model; a CFD-DEM coupling simulation method is adopted; establishing and setting a numerical model; calibrating parameters; setting working conditions; carrying out CFD-DEM model coupling calculation; and evaluating the smoke blocking performance of the air curtain. According to the method, the CFD-DEM coupling model is established, so that the smoke blocking performance of the air curtain in the bifurcated tunnel can be systematically evaluated; by running a CFD-DEM coupling solving program, the motion trail and the stress condition of dust particles under the action of an air curtain can be obtained; by changing the parameters of the main tunnel longitudinal ventilation-air curtain ventilation system, such as the air curtain spraying angle, spraying speed and thickness and the main tunnel longitudinal wind speed, the dust removal effects under different working conditions can be analyzed; based on the simulation result, the design and parameter adjustment of the air curtain can be optimized.

Description

Technical Field

[0001] The invention belongs to the field of ventilation and fire prevention and control design of bifurcated tunnels, and in particular relates to a method for evaluating the smoke blocking performance of an air curtain in a bifurcated tunnel. Background Art

[0002] In the urban transportation network, bifurcated tunnels, due to their special structural form, pose challenges to smoke control under ventilation and fire conditions. For tunnels with branches, attention should be paid not only to the spread of smoke in the main tunnel, but also to the safety issues in the branch tunnels, and smoke should be prevented from entering the branch tunnels as much as possible, otherwise people escaping will pass through smoke-dense areas, which is very likely to cause casualties.

[0003] Air curtain dust removal technology in bifurcated tunnels is an effective solution, but how to evaluate its performance remains a challenge. Existing technologies mainly focus on the top smoke exhaust-air curtain system of a single tunnel, while relatively few studies have been conducted on the longitudinal ventilation-air curtain system of bifurcated tunnels. This leads to many uncertainties in how to effectively control the diffusion and emission of smoke in bifurcated tunnels, especially under fire conditions. Summary of the invention

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

[0005] The technical solution of the present invention is: a method for evaluating the smoke blocking performance of an air curtain in a bifurcated tunnel, comprising the following steps: S1. Establish a bifurcated tunnel model: Establish a tunnel model, and take the main tunnel and ramp with a certain length before and after the bifurcation as the calculation domain; S2. Setting numerical simulation method: adopting 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; S3. Establish and set up the numerical model: Based on DEM, complete the setting of the particle factory, including: the number of particles generated per second, particle grading, and basic particle size; Based on DEM, complete the setting of smoke particle parameters, including: particle temperature, particle thermal conductivity, microscopic parameters of particle-plane contact model, microscopic parameters of particle-particle contact, and particle grading; Based on CFD, complete the setting of the 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, and main tunnel longitudinal wind speed; S4. Calibration parameters: Conduct material combustion test, collect the granular materials obtained after the same fire source material is burned and measure the smoke temperature; perform DEM numerical simulation of drum test by discrete element method to obtain DEM particle-plane contact parameters; perform DEM numerical simulation of angle of repose test by discrete element method to obtain DEM particle-particle contact parameters; then conduct fire scale experiment, perform CFD numerical simulation of fire scale experiment by computational fluid dynamics method, compare the smoke temperature, DEM particle-plane contact parameters and DEM particle-particle contact parameters obtained from the above test with the results of CFD numerical simulation, adjust and calibrate the smoke temperature, DEM particle-plane contact parameters and DEM particle-particle contact parameters; S5. Setting working conditions: Select air curtain parameters, including air curtain thickness, jet velocity, and jet angle. Set multiple groups of cross working conditions according to the parameters and the number of data corresponding to each parameter to fully reflect the impact of air curtain parameter changes on smoke blocking effects. S6. Run the solution program and output the result data: CFD-DEM model coupling calculation, obtain the particle motion trajectory and force magnitude based on the DEM calculation results, and obtain the air flow field distribution based on the CFD calculation results; S7. Evaluate the smoke-blocking performance of the air curtain: Based on the particle movement trajectory and force magnitude, the movement pattern of smoke particles under the combined action of the longitudinal wind in the main tunnel and the air curtain jet air is obtained, and its movement law at the ramp is analyzed; the influence of particles on the fluid is analyzed based on the distribution of different physical quantities in the air flow field; the smoke-blocking performance of the air curtain is evaluated by analyzing the interaction between smoke particles and air at the ramp entrance.

[0006] As a further improvement of the present invention, in step S2, when performing numerical simulation of air flow field, a 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; The continuity equation is expressed as: Among them, ρf is the air density, u is the average gas velocity, ε is the gas void fraction, represents the gradient; The momentum equation is expressed as: Where 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.

[0007] As a further improvement of the present invention, in step S2, when performing numerical simulation of smoke particles, a solid phase (smoke particle) motion control equation is established according to the DEM method, and the solid phase control equation includes a particle translation equation and a particle rotation equation; The particle translation equation is expressed as: Among them, 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 between particle i and air fluid; The particle rotation equation is expressed as: Among them, ω i is the angular velocity of particle i, T ij is the tangential moment between particles, M ij is the rolling friction torque between particles, I i is the particle moment of inertia.

[0008] There is interaction force between air and particles in the established fluid phase control equation and solid phase control equation. Through this interaction force, the DEM and CFD methods can be coupled for calculation.

[0009] As a further improvement of the present invention, in step S3, when setting up the particle factory based on DEM, the geometric features of the particle factory are set to a surface domain, which is attached to the top of the inner wall of the tunnel. Driven by the longitudinal wind, it flows toward the bifurcation. Due to its low density, it moves along the top of the inner wall of the tunnel, simulating the flow of real smoke.

[0010] As a further improvement of the present invention, in step S3, when setting the smoke particle parameters based on DEM, the particle temperature is directly calibrated by experiments, and the particle grading, particle thermal conductivity, microscopic parameters of the particle-plane contact model, and microscopic parameters of particle-particle contact are calibrated by combining experiments with numerical simulations.

[0011] As a further improvement of the present invention, in step S3, the boundary condition is set as follows: the plane corresponding to the tunnel inlet and outlet is the default pressure outlet.

[0012] The beneficial effects of the present invention are: 1. Evaluate the smoke barrier performance of air curtains in bifurcated tunnels: By establishing a CFD-DEM coupling model, the smoke barrier performance of air curtains in bifurcated tunnels can be systematically evaluated. The model takes into account the interaction between air flow field, dust particle distribution and air curtain, and can provide more accurate and comprehensive evaluation results.

[0013] 2. Quantitative analysis of the movement trajectory and stress of dust particles: By running the CFD-DEM coupling solution program, the movement trajectory and stress of dust particles under the action of the air curtain can be obtained. This helps to understand the distribution and migration of particles in the tunnel and provide a basis for optimizing the air curtain design and parameter adjustment.

[0014] 3. Evaluate the smoke blocking effect under different working conditions: By changing the parameters of the main tunnel longitudinal ventilation-air curtain ventilation system, such as the air curtain spray angle, spray speed, thickness and the main tunnel longitudinal wind speed, the dust removal effect under different working conditions can be analyzed. This helps to find the optimal design solution and improve the dust removal efficiency of the air curtain.

[0015] 4. Optimize air curtain design and parameter adjustment: Based on the simulation results, the design and parameter adjustment of the air curtain can be optimized. For example, by analyzing the movement trajectory and force of the particles, the angle, speed, thickness and other parameters of the air curtain can be adjusted to better control the diffusion and emission of dust particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the fire condition diagram of the bifurcated tunnel; Figure 2 is the velocity flow field diagram at the tunnel bifurcation; Figure 3 It is the vector diagram of the velocity flow field at the tunnel bifurcation.

[0017] In the figure, 1-main tunnel; 2-ramp; 3-air curtain; 4-fire source; 5-longitudinal wind. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to the accompanying drawings.

[0019] Embodiment 1, Fire conditions such as Figure 1 As shown, an air curtain 3 is provided at the bifurcation of the main tunnel 1 and the ramp 2 , and a fire source 4 is provided in the longitudinal wind 5 direction of the main tunnel 1 .

[0020] A method for evaluating the smoke barrier performance of an air curtain in a bifurcated tunnel, characterized by comprising the following steps: S1. Establish a bifurcated tunnel model: Establish a tunnel model, and take the main tunnel and ramp with a certain distance before and after the bifurcation as the calculation domain. In order to shorten the numerical simulation time, the inner contour of the tunnel section remains unchanged during modeling, and the outer contour of the tunnel section is set to a simple geometric shape, such as a rectangle.

[0021] S2. Setting the numerical simulation method: Using the 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.

[0022] (1) When performing numerical simulation of air flow field, the fluid phase (air) 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: Among them, ρf is the air density, u is the average gas velocity, ε is the gas void fraction, represents the gradient; The momentum equation is expressed as: Where 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.

[0023] (2) When performing numerical simulation of smoke particles, the solid phase (smoke particle) motion control equation is established according to the DEM method. The solid phase control equation includes the particle translation equation and the particle rotation equation; The particle translation equation is expressed as: Among them, 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 between particle i and air fluid; The particle rotation equation is expressed as: Among them, ω i is the angular velocity of particle i, T ij is the tangential moment between particles, M ij is the rolling friction torque between particles, I i is the particle moment of inertia.

[0024] There is interaction force between air and particles in the established fluid phase control equation and solid phase control equation. Through this interaction force, the DEM and CFD methods can be coupled for calculation.

[0025] S3. Establish and set up the numerical model: (1) Based on DEM, the particle factory is set up, including the number of particles generated per second, particle grading, and basic particle size. The particle factory geometric features are set as a surface domain, which is attached to the inner wall of the tunnel. Driven by the longitudinal wind, it flows toward the bifurcation. Due to its low density, it moves along the inner wall of the tunnel, simulating the flow of real smoke.

[0026] (2) Based on DEM, the smoke particle parameters are set, including particle temperature, particle thermal conductivity, mesoscopic parameters of the particle-plane contact model, mesoscopic parameters of particle-particle contact, and particle grading. The particle temperature is calibrated directly by experiments, while the particle grading, particle thermal conductivity, mesoscopic parameters of the particle-plane contact model, and mesoscopic parameters of particle-particle contact are calibrated by combining experiments with numerical simulations.

[0027] (3) Based on CFD, complete the setting of 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, and main tunnel longitudinal wind speed;

[0028] (4) Set the boundary conditions as follows: the plane corresponding to the tunnel inlet and outlet is the default pressure outlet.

[0029] S4. Calibration parameters: Conduct material combustion test, collect the granular materials obtained after the combustion of the same fire source materials and measure the smoke temperature; perform DEM numerical simulation of the drum experiment by discrete element method to obtain DEM particle-plane contact parameters; perform DEM numerical simulation of the angle of repose experiment by discrete element method to obtain DEM particle-particle contact parameters; then conduct fire scale experiment, and perform CFD numerical simulation of the fire scale experiment by computational fluid dynamics method, compare the smoke temperature, DEM particle-plane contact parameters, and DEM particle-particle contact parameters obtained from the above experiments with the results of CFD numerical simulation, and adjust and calibrate the smoke temperature, DEM particle-plane contact parameters, and DEM particle-particle contact parameters.

[0030] S5. Set working conditions: select air curtain parameters, including air curtain thickness, jet velocity, and jet angle, consider the actual value range of the parameters, determine the data for each group of parameters, set multiple groups of cross working conditions according to the parameters and the number of data corresponding to each parameter, and fully reflect the impact of changes in air curtain parameters on the smoke blocking effect.

[0031] S6. Run the solution program and output the result data: CFD-DEM model coupling calculation, obtain the particle motion trajectory and force magnitude based on the DEM calculation results, and obtain the air flow field distribution based on the CFD calculation results.

[0032] S7. Evaluate the smoke-blocking performance of the air curtain: Based on the particle movement trajectory and the magnitude of the force, the movement pattern of the smoke particles under the combined action of the longitudinal wind in the main tunnel and the air curtain jet air is obtained, and the movement law of the smoke particles at the ramp is analyzed. The smoke particles show a random movement state at the fork, but generally still show the law of entering and leaving the ramp; based on the distribution of different physical quantities in the air flow field, the influence of the particles on the fluid is analyzed; such as Figure 2As shown in the figure, the jet of the air curtain is discharged from the air outlet at a certain speed. Although this part of the gas fails to completely contact the ground and the ramp, the jet continuously sucks the surrounding air and smoke and exchanges heat with the surrounding gas. The wind field with a lower speed below connects the airflow blown out from the upper part to form a continuous curtain-like airflow. Since the mixed airflow is very similar to the curtain-like airflow formed by the conventional air curtain, it is called the "equivalent air curtain"; Figure 3 It can be seen that a vortex will be formed on the right side of the equivalent air curtain. Since the longitudinal wind of the main tunnel will affect the airflow ejected by the air curtain at the fork, the longitudinal wind in the main tunnel and the wind blown out of the air curtain perpendicular to the cross section are vector superimposed in different directions, and a vortex is formed under the joint action of the two. By analyzing the interaction between smoke particles and air at the ramp mouth, the smoke-blocking performance of the air curtain is evaluated. The flow field distribution of the ventilation system of the longitudinal wind-air curtain system at the fork is already very complex. In addition, the disturbance of many tiny particles generated by the fire smoke at the fork makes the performance evaluation of the air curtain more difficult. Through the above analysis of the movement law and the influence of particles on the fluid, the flow field at the fork presents an "equivalent air curtain" state as a whole. Under the action of this flow field, although the particles move in a disorderly manner, they still show the law of rolling in and out of the ramp as a whole. By changing the working parameters, the relative size of the rolling in and out capacity changes, resulting in a change in the length of smoke spreading on the ramp, thereby exploring the smoke-blocking performance of the air curtain.

[0033] Based on the complexity of the longitudinal wind-air curtain ventilation system and the complexity of the flow field at the tunnel bifurcation, the present invention establishes a CFD-DEM coupling model, and adopts the coupling simulation technology of CFD and DEM, which can comprehensively consider the distribution and movement of the air flow field and dust particles, and provide more accurate simulation results. Through this model, the interaction between the air curtain and the flow field in the tunnel, as well as the movement trajectory of dust particles under the action of the air curtain, can be simulated. The present invention uses CFD-DEM coupling technology to systematically evaluate the dust removal performance of the air curtain in the bifurcated tunnel, which can be widely used in the ventilation and fire prevention and control design fields of bifurcated tunnels. This method can not only be used to evaluate the performance of existing bifurcated tunnels, but also provide guidance for newly designed bifurcated tunnels.

[0034] The evaluation method of the present invention can be extended to other similar structures and systems, such as large underground interchange tunnels, highway intersection tunnels, etc., and can be used in scenarios where dust or smoke diffusion needs to be controlled.

Claims

1. A method for evaluating the smoke barrier performance of an air curtain in a bifurcated tunnel, characterized in that The following steps are involved: S1. Establish a bifurcated tunnel model: Establish a tunnel model, and take the main tunnel and ramp with a certain length before and after the bifurcation as the calculation domain; S2. Setting numerical simulation method: adopting 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; S3. Establish and set up the numerical model: Based on DEM, complete the setting of the particle factory, including: the number of particles generated per second, particle grading, and basic particle size; Based on DEM, complete the setting of smoke particle parameters, including: particle temperature, particle thermal conductivity, microscopic parameters of particle-plane contact model, microscopic parameters of particle-particle contact, and particle grading; Based on CFD, complete the setting of the 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, and main tunnel longitudinal wind speed; S4. Calibration parameters: Conduct material combustion test, collect the granular materials obtained after the same fire source material is burned and measure the smoke temperature; perform DEM numerical simulation of drum test by discrete element method to obtain DEM particle-plane contact parameters; perform DEM numerical simulation of angle of repose test by discrete element method to obtain DEM particle-particle contact parameters; then conduct fire scale experiment, perform CFD numerical simulation of fire scale experiment by computational fluid dynamics method, compare the smoke temperature, DEM particle-plane contact parameters and DEM particle-particle contact parameters obtained from the above test with the results of CFD numerical simulation, adjust and calibrate the smoke temperature, DEM particle-plane contact parameters and DEM particle-particle contact parameters; S5. Setting working conditions: Select air curtain parameters, including air curtain thickness, jet velocity, and jet angle. Set multiple groups of cross working conditions according to the parameters and the number of data corresponding to each parameter to fully reflect the impact of air curtain parameter changes on smoke blocking effects. S6. Run the solution program and output the result data: CFD-DEM model coupling calculation, obtain the particle motion trajectory and force magnitude based on the DEM calculation results, and obtain the air flow field distribution based on the CFD calculation results; S7. Evaluate the smoke-blocking performance of the air curtain: Based on the particle movement trajectory and force magnitude, the movement pattern of smoke particles under the combined action of the longitudinal wind in the main tunnel and the air curtain jet air is obtained, and its movement law at the ramp is analyzed; the influence of particles on the fluid is analyzed based on the distribution of different physical quantities in the air flow field; the smoke-blocking performance of the air curtain is evaluated by analyzing the interaction between smoke particles and air at the ramp entrance.

2. The method for evaluating the smoke barrier performance of an air curtain in a bifurcated tunnel according to claim 1, characterized in that: In step S2, when performing numerical simulation of the air flow field, a fluid phase control equation is established based on the CFD method, and the fluid phase control equation includes a continuity equation and a momentum equation; The continuity equation is expressed as: Among them, ρ f is the air density, u is the average gas velocity, ε is the gas void fraction, represents the gradient; The momentum equation is expressed as: Where 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.

3. A method for evaluating the smoke blocking performance of an air curtain in a bifurcated tunnel according to claim 1 or 2, characterized in that: In step S2, when performing numerical simulation of smoke particles, a solid phase motion control equation is established according to the DEM method, and the solid phase control equation includes a particle translation equation and a particle rotation equation; The particle translation equation is expressed as: Among them, 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 between particle i and air fluid; The particle rotation equation is expressed as: Among them, ω i is the angular velocity of particle i, T ij is the tangential moment between particles, M ij is the rolling friction torque between particles, I i is the particle moment of inertia.

4. The method for evaluating the smoke barrier performance of an air curtain in a bifurcated tunnel according to claim 1, characterized in that: In step S3, when setting up the particle factory based on DEM, the particle factory geometric features are set to a surface area, which is attached to the top of the inner wall of the tunnel. Driven by the longitudinal wind, it flows toward the bifurcation. Due to its low density, it moves along the top of the inner wall of the tunnel, simulating the flow of real smoke.

5. A method for evaluating the smoke blocking performance of an air curtain in a bifurcated tunnel according to claim 1 or 4, characterized in that: In step S3, when setting smoke particle parameters based on DEM, the particle temperature is directly calibrated by experiments, and the particle grading, particle thermal conductivity, microscopic parameters of the particle-plane contact model, and microscopic parameters of particle-particle contact are calibrated by combining experiments with numerical simulations.

6. A method for evaluating the smoke blocking performance of an air curtain in a bifurcated tunnel according to claim 1 or 4, characterized in that: In step S3, the boundary condition is set as follows: the plane corresponding to the tunnel inlet and outlet is the default pressure outlet.

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