Method for predicting thickness of flue gas layer of V-shaped slope tunnel of water-adding spraying system

Abstract

The invention relates to a method for predicting the thickness of a flue gas layer in a V-shaped slope tunnel of a water-adding spraying system. The smoke layer thickness prediction method comprises the following steps: determining a fire scene according to a tunnel structure and a gradient, establishing a tunnel model in fire dynamics simulation software FDS, setting basic parameters of the tunnel model, and dividing grids; influence factors and basic physical quantities of the smoke layer thickness are determined, non-dimensional items of the influence factors are obtained according to the pi theorem, and a non-dimensional calculation formula of the smoke layer thickness is deduced; changing the gradient of the tunnel, the fire source power and the water spray flow, and performing numerical simulation to obtain the thickness value of the flue gas layer in the tunnel under different working conditions; and drawing the simulation result into a scatter diagram and carrying out nonlinear fitting to obtain the value of each unknown coefficient in the dimensionless relational expression so as to construct the model for predicting the thickness of the flue gas layer in the dimensionless V-shaped slope tunnel. The method is suitable for tunnel flue gas layer thickness prediction when a symmetric V-shaped slope tunnel fire disaster with different fire source powers, different water spray flows and different gradients occurs.

Description

Technical Field

[0001] The present invention belongs to the field of tunnel fire prevention and smoke exhaust, and is suitable for predicting the thickness characteristics of smoke layers in symmetrical "V"-shaped slope tunnels with water spray fire extinguishing systems. Background Art

[0002] With the advancement of science and technology, the construction and widespread use of tunnels have greatly facilitated human life, but this has also led to an increase in fire hazards. Underwater tunnels, crossing rivers, lakes, or oceans, have steep slopes and elevation differences between the sides and the center, resulting in a "V"-shaped structure. While these tunnels fulfill their functions, they also present significant fire hazards. The unique "V"-shaped tunnel structure makes vehicles more susceptible to collisions and fires. Fire smoke can quickly spread and accumulate below. Statistics show that over 85% of casualties die from inhalation of smoke and toxic fumes, leading to coma. Stable, high smoke stratification can minimize the impact of fire smoke on evacuation efforts below. To improve fire prevention capabilities, key tunnels, including "V"-shaped underwater tunnels, are gradually installing water spray systems. Water spray systems can reduce the temperature of fire smoke. However, they can disrupt the stable smoke layer, causing smoke settling and endangering the safety of evacuees. Studying the impact of water spray systems on smoke stratification in "V"-shaped tunnels is crucial for effective smoke control and optimizing system parameters.

[0003] Current research on tunnel fire smoke focuses on smoke stratification, smoke spread characteristics, and smoke temperature through experimental and numerical simulations. Furthermore, most studies, both domestically and internationally, have been conducted in horizontal tunnels with water spray systems or in sloped tunnels without them. The impact of the combined effects of these two methods on smoke layer characteristics has been less studied. Currently, there are no methods specifically designed to calculate the smoke layer thickness in "V"-shaped tunnels, taking into account the effect of tunnel water spray flow rate. Summary of the Invention

[0004] This invention aims to address the current problem of slope-independent smoke layer thickness prediction methods in tunnel fire simulations using water spray systems. By employing fire source models with varying fire power, this paper provides an effective method for predicting smoke layer thickness in tunnel fires with V-shaped slopes using water spray systems.

[0005] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0006] A method for predicting the thickness of the smoke layer in a V-shaped slope tunnel using a water spray system comprises the following steps:

[0007] 1) Determine the basic setting parameters for the fire scene simulation in the tunnel based on the physical structure of the tunnel and the setting of the water spray system in the tunnel, and establish a physical model for the tunnel fire simulation in the FDS software;

[0008] 2) Determine the factors affecting the thickness of the smoke layer in the tunnel and establish a relationship between the thickness h of the smoke layer and the factors.

[0009] 3) determining the basic physical quantities of the influencing factors, obtaining the dimensionless terms of the influencing factors according to the π theorem, and then converting the dimensional relationship in step 2) into a dimensionless relationship to obtain a dimensionless calculation formula for the smoke layer thickness h;

[0010] 4) Using the influencing factors as variables, numerical simulation calculations are performed through FDS to obtain the smoke layer thickness values ​​h under different conditions; the simulation results are plotted as a scatter plot to clarify the impact of each influencing factor on the smoke layer thickness h;

[0011] 5) Performing nonlinear fitting on the results of the scatter plot to obtain the values ​​of the unknown coefficients in the dimensionless calculation formula in step 3), and then constructing a dimensionless prediction model for the smoke layer thickness h in a "V"-shaped slope tunnel of a water spray system.

[0012] Based on the above solution, the present invention can be improved as follows.

[0013] Furthermore, in step 1), the basic setting parameters include tunnel model size, tunnel slope i, fire source power Q, and water spray flow rate q;

[0014] Furthermore, the dimensions of the tunnel model are 600m long × 13.2m wide × 8.1m high. In the model tunnel, temperature slices are arranged longitudinally through the tunnel. Starting from 3m away from the fire source, 27 groups of vertical temperature measuring points and flow velocity measuring points are set at intervals of 1.5m on the left and right.

[0015] Furthermore, the slopes on both sides of the tunnel are consistent and are set to 0%, 3% and 5% respectively;

[0016] Furthermore, the fire source has a size of 4.5m x 3m, is 0.2m away from the bottom of the tunnel, and has a power of 5MW, 10MW, 15MW, 20MW, and 25MW;

[0017] Furthermore, water spray nozzles were installed at 4.5m height on both sides of the V-shaped tunnel between 0 and 120m from the slope change point, spaced 5m apart. The spray flow rates were set to 0L / min, 10L / min, 50L / min, 100L / min, 200L / min, 400L / min, and 600L / min.

[0018] Furthermore, in step 2), the influencing factors in the tunnel include the fire source heat release rate Q, the tunnel height H, the symmetrical V-shaped slope tunnel slope i, the ambient air temperature T ∞ , ambient air density ρ ∞ , constant pressure specific heat capacity of air cp , gravitational acceleration g, water spray system flow rate q.

[0019] Furthermore, in step 2), the relationship between the smoke layer thickness h and the influencing factors is:

[0020] f(h,Q,H,i,T ∞ ,ρ ∞ ,C p ,g,q)=0

[0021] Furthermore, in step 3), the basic physical quantities are the tunnel height H, the ambient air temperature T ∞ , ambient air density ρ ∞ , gravitational acceleration g.

[0022] Furthermore, by introducing the π theorem, we can obtain:

[0023]

[0024] Furthermore, in step 3), the dimensionless term of the influencing factor is:

[0025]

[0026] Furthermore, in step 3), the dimensionless calculation formula for the smoke layer thickness h is:

[0027]

[0028] Right now:

[0029] h * =f(Q * ,i,q * )

[0030] Compared with existing technologies, the present invention offers the following advantages: theoretically, it applies the π theorem and dimensional analysis, laying a solid theoretical foundation; in practical application, the numerical simulation method is simple, and parameters can be set according to the actual tunnel conditions. Taking into account the unique structural characteristics of V-shaped slope tunnels with water spray, the influence of water spray flow rate, tunnel slope, and fire source power on the smoke layer thickness within the tunnel is determined. This method is applicable to predicting smoke layer thickness within V-shaped slope tunnels with various slopes, fire source powers, and water spray flow rates. Simulations show a high degree of agreement with the prediction formula, validating the scientific and practical nature of this method. This method complements traditional single-slope tunnel research, which has not considered V-shaped slope tunnels with water spray, and improves the prediction formula for smoke layer thickness within sloped tunnels. This method considers virtually all influencing factors in the derivation of dimensional relationships, resulting in more innovative and instructive results. Predicting and calculating smoke layer thickness can provide guidance for smoke control and firefighting rescue in V-shaped slope tunnels with water spray. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of the numerical simulation of a fire in a “V”-shaped slope tunnel using a water spray system according to the present invention.

[0032] Figure 2 This is a schematic diagram of the fire simulation in a “V”-shaped slope tunnel according to the present invention.

[0033] Figure 3 This is an analysis diagram of the grid independence and simulation accuracy of the present invention.

[0034] Figure 4 This is a graph showing the variation of smoke layer thickness with water spray flow rate in tunnels with different slopes according to the present invention.

[0035] Figure 5 This is a diagram showing the relationship between smoke layer thickness and flow rate in the present invention.

[0036] Figure 6 This is the relationship diagram between the tunnel slope and coefficient of the present invention.

[0037] Figure 7 This is a model diagram for calculating the thickness of the smoke layer in a symmetrical "V"-shaped slope tunnel under the action of the water spray system of the present invention.

[0038] Figure 8 This is the algorithm flow chart of the present invention using FDS to numerically simulate "V"-shaped slope tunnel fire. DETAILED DESCRIPTION

[0039] 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 used to explain the present invention and are not used to limit the scope of the present invention.

[0040] like Figures 1 to 8 As shown, the present invention provides a method for predicting smoke layer characteristics in a symmetrical "V"-shaped slope tunnel fire with a water spray fire extinguishing system, comprising the following specific steps:

[0041] 1) Based on the physical structure of the tunnel and the setting of the water spray system in the tunnel, the basic setting parameters for the fire scene simulation in the tunnel are determined. A physical model of the tunnel fire simulation is established in the FDS software, and the grid is divided for independence analysis to verify the reliability of the model.

[0042] 2) Determine the factors affecting the thickness of the smoke layer in the tunnel and establish a relationship between the thickness h of the smoke layer and the factors.

[0043] 3) determining the basic physical quantities of the influencing factors, obtaining the dimensionless terms of the influencing factors according to the π theorem, and then converting the dimensional relationship in step 2) into a dimensionless relationship to obtain a dimensionless calculation formula for the smoke layer thickness h;

[0044] 4) Using the influencing factors as variables, numerical simulation calculations are performed through FDS to obtain the smoke layer thickness values ​​h under different conditions; the simulation results are plotted as a scatter plot to clarify the impact of each influencing factor on the smoke layer thickness h;

[0045] 5) Performing nonlinear fitting on the results of the scatter plot to obtain the values ​​of the unknown coefficients in the dimensionless calculation formula in step 3), and then constructing a dimensionless prediction model for the smoke layer thickness h in a "V"-shaped slope tunnel of a water spray system.

[0046] In the present invention, in step 1), the basic setting parameters include tunnel model size, tunnel slope i, fire source power Q, and water spray flow rate q;

[0047] In the present invention, the tunnel model has the dimensions of 600m long × 13.2m wide × 8.1m high. In the model tunnel, a temperature slice is laid longitudinally through the tunnel. Starting from 3m away from the fire source, 27 groups of vertical temperature measuring points and flow velocity measuring points are set at intervals of 1.5m. Figure 2 shown.

[0048] In the present invention, the slopes on both sides of the tunnel are consistent and are set to 0%, 3% and 5% respectively;

[0049] In the present invention, the fire source size is 4.5m×3m, 0.2m away from the bottom of the tunnel, and the fire source power is 5MW, 10MW, 15MW, 20MW, and 25MW;

[0050] In the present invention, water spray nozzles are installed at a height of 4.5 m on both sides of the V-shaped tunnel at a distance of 0 to 120 m from the slope change point, with a spacing of 5 m. The water spray flow rate is set to 0 L / min, 10 L / min, 50 L / min, 100 L / min, 200 L / min, 400 L / min, and 600 L / min.

[0051] In this invention, the accuracy of the FDS calculation is closely related to the size of the grid. The finer the grid division, the more accurate the calculation results, but the calculation time will increase significantly. NIST has verified that when the grid size is adapted to the formula d = 1 / 16D* to 1 / 4D*, the simulation has higher accuracy. D* is the combustion characteristic diameter, calculated as:

[0052]

[0053] Where: D* is the characteristic diameter of combustion (m); Q is the heat release rate of the fire source (kW); T ∞ is the ambient air temperature (K); ρ ∞ is the ambient air density (kg / m 3 ), take ρ∞ =1.2kg / m 3 ;c p is the constant pressure specific heat capacity of air (kJ / (kg·K)), take c p =1.02kJ / (kg·K)); g acceleration due to gravity (m / s 2 ), take g = 9.81 m / s 2 . Make model validation visible Figure 3 .

[0054] In the present invention, in step 2), the influencing factors in the tunnel are the fire source heat release rate Q, the tunnel height H, the symmetrical V-shaped slope tunnel slope i, the ambient air temperature T ∞ , ambient air density ρ ∞ , constant pressure specific heat capacity of air c p , gravitational acceleration g, water spray system flow rate q.

[0055] In the present invention, in step 2), the relationship between the smoke layer thickness h and the influencing factors is:

[0056] f(h,Q,H,i,T ∞ ,ρ ∞ ,C p ,g,q)=0

[0057] In the present invention, in step 3), the basic physical quantities are the tunnel height H, the ambient air temperature T ∞ , ambient air density ρ ∞ , gravitational acceleration g.

[0058] In the present invention, the π theorem is introduced to obtain:

[0059]

[0060] In the present invention, in step 3), the dimensionless term of the influencing factor is:

[0061]

[0062] In the present invention, in step 3), the dimensionless calculation formula for the smoke layer thickness h is:

[0063]

[0064] Right now:

[0065] h * =f(Q * ,i,q * )

[0066] In the present invention, in step 4), the working condition table simulated by FDS is shown in Table 1

[0067] Table 1 Numerical simulation conditions

[0068]

[0069] According to Table 1, numerical simulation is carried out and the average thickness of the smoke layer between 10m and 30m from the fire source in the water spray system action area is selected as the research and analysis object. A scatter plot is drawn. Figure 4 The curves of smoke layer thickness in tunnels with different slopes and water spray flow rate are shown in Figure 2. As can be seen from the figure, the thickness of the smoke layer in the tunnel generally shows a trend of decreasing as the water spray flow rate increases.

[0070] The fire source heat release rate Q, tunnel slope i, and water spray system flow rate q are important factors affecting the thickness of the smoke layer in the tunnel. The smoke layer thickness is positively correlated with smoke production. Based on existing fire plume mass flow models, smoke production and the fire source heat release rate have a power function relationship, resulting in:

[0071]

[0072] Figure 5 The relationship between the thickness of the smoke layer and the flow rate of the water spray system is shown in the figure. The two are linearly related. The data are fitted using the origin software to obtain a linear expression, R 2 All of them are above 0.92, and the fitting correlation is high.

[0073] The fitted values ​​of the slope K and intercept B are summarized in Table 2.

[0074] Table 2 Slope K and intercept B fitting values

[0075]

[0076] Figure 6 To study the relationship between tunnel slope and the coefficient of the linear expression, a distribution curve between tunnel slope and coefficient was drawn. As can be seen from the figure, there is a good linear relationship between tunnel slope and both slope K and intercept B.

[0077] Finally, after calculation and fitting, the above data are summarized and brought in to give the dimensionless smoke layer thickness h in the symmetrical "V" slope tunnel. * and tunnel slope i, dimensionless fire source heat release rate Q * , the calculation model of the dimensionless water spray system flow rate q* is:

[0078] h * =[(2.50i-0.35)q * +(-2.69i+1.08)]Q*0.33

[0079] Figure 7 The distribution of the simulated data near the fitting formula is shown in Figure 2. It can be seen that the simulated data are evenly scattered near the isoequivalent line, indicating that the fitting effect is relatively good.

[0080] The beneficial effects of this invention are as follows: theoretically, the application of the π theorem and dimensional analysis lays a theoretical foundation; in practical application, the numerical simulation method is simple, and parameters can be set according to the actual conditions of the tunnel. Taking into account the particularities of the "V"-shaped slope tunnel structure with water spray, the influence of water spray flow rate, tunnel slope, and fire source power on the thickness of the smoke layer within the tunnel is determined. This method is applicable to the prediction of smoke layer thickness in "V"-shaped slope tunnels with different slopes, fire source powers, and different water spray flow rates. Simulations showed a high degree of agreement with the prediction formula, verifying the scientific and practical nature of this method. This method supplements the traditional single-slope tunnel research that does not consider the case of "V"-shaped slope tunnels with water spray, and improves the prediction formula for smoke layer thickness in sloped tunnels. This method considers essentially all influencing factors in the derivation of dimensional relationships, resulting in more innovative and instructive results. Predicting and calculating the smoke layer thickness can provide guidance for smoke control and firefighting rescue in "V"-shaped slope tunnels with water spray.

[0081] 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 in the scope of protection of the present invention.

Claims

1. A method for predicting the thickness of the smoke layer in a V-shaped slope tunnel with a water spray system, characterized in that: The following steps are involved: 1) Determine the basic setting parameters for the fire scene simulation in the tunnel based on the physical structure of the tunnel and the setting of the water spray system in the tunnel, and establish a physical model for the tunnel fire simulation in the FDS software; 2) Determine the factors affecting the thickness of the smoke layer in the tunnel and establish a relationship between the thickness h of the smoke layer and the factors. 3) determining the basic physical quantities of the influencing factors, obtaining the dimensionless terms of the influencing factors according to the π theorem, and then converting the dimensional relationship in step 2) into a dimensionless relationship to obtain a dimensionless calculation formula for the smoke layer thickness h; 4) Using the influencing factors as variables, numerical simulation calculations are performed through FDS to obtain the smoke layer thickness values ​​h under different conditions; the simulation results are plotted as a scatter plot to clarify the impact of each influencing factor on the smoke layer thickness h; 5) Performing nonlinear fitting on the results of the scatter plot to obtain the values ​​of the unknown coefficients in the dimensionless calculation formula in step 3), and then constructing a dimensionless prediction model for the smoke layer thickness h in a "V"-shaped slope tunnel with a water spray system.

2. The method for predicting smoke layer thickness in a V-shaped slope tunnel with a water spray system according to claim 1 is characterized in that: In step 1), the three-dimensional model of the tunnel, the basic setting parameters include tunnel model size, tunnel slope i, fire source power Q, and water spray flow rate q.

3. The method for predicting smoke layer thickness in a V-shaped slope tunnel with a water spray system according to claim 2 is characterized in that: Step 1) The tunnel model has dimensions of 600 m long × 13.2 m wide × 8.1 m high. In the model tunnel, temperature slices are arranged longitudinally through the tunnel. Starting at 3 m from the fire source, 27 groups of vertical temperature measuring points and flow velocity measuring points are set at intervals of 1.5 m on the left and right.

4. The method for predicting smoke layer thickness in a V-shaped slope tunnel with a water spray system according to claim 3 is characterized in that: Step 1) The slopes on both sides of the tunnel are consistent and are set to 0%, 3% and 5% respectively; the fire source size is 4.5m×3m, 0.2m away from the bottom of the tunnel, and the fire source power is 5MW, 10MW, 15MW, 20MW, and 25MW.

5. The method for predicting smoke layer thickness in a V-shaped slope tunnel with a water spray system according to claim 4 is characterized in that: In step 1), water spray nozzles were installed at a height of 4.5 m on both sides of the V-shaped tunnel at a distance of 0 to 120 m from the slope change point, with a spacing of 5 m. The water spray flow rate was set to 0 L / min, 10 L / min, 50 L / min, 100 L / min, 200 L / min, 400 L / min, and 600 L / min.

6. The method for predicting smoke layer thickness in a V-shaped slope tunnel with a water spray system according to claim 5 is characterized in that: In step 2), the influencing factors in the tunnel are the fire source heat release rate Q, tunnel height H, symmetrical V-shaped slope tunnel slope i, ambient air temperature T ∞ , ambient air density ρ ∞ , constant pressure specific heat capacity of air c p , gravitational acceleration g, water spray system flow rate q.

7. The method for predicting smoke layer thickness in a V-shaped slope tunnel with a water spray system according to claim 6 is characterized in that: In step 2), the relationship between the smoke layer thickness h and the influencing factors is: f(h,Q,H,i,T ∞ ,ρ ∞ ,C p ,g,q)=0 8. The method for predicting smoke layer thickness in a V-shaped slope tunnel with a water spray system according to claim 7 is characterized in that: In step 2), the basic physical quantities are tunnel height H, ambient air temperature T ∞ , ambient air density ρ ∞ , gravitational acceleration g.

9. The method for predicting smoke layer thickness in a V-shaped slope tunnel with a water spray system according to claim 8 is characterized in that: In step 3), the dimensionless term of the influencing factor is:

10. The method for predicting smoke layer thickness in a V-shaped slope tunnel with a water spray system according to claim 9 is characterized in that: In step 3), the dimensionless calculation formula for the smoke layer thickness h is: Right now: h * =f(Q * ,i,q * )

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