CN113312771B - Calculation method and application of limited wind speed of side key smoke exhaust of tunnel - Google Patents

Abstract

The invention relates to a method for calculating limited wind speed of side key smoke exhaust of a tunnel and application thereof, comprising the following specific steps of: determining a limited wind speed u_cDefining, determining influencing factors, establishing a limited wind speed u_cA relationship to an influencing factor; determining basic dimension, and establishing limited wind speed u_cA dimensional relation with the influencing factor; determining basic physical quantity, obtaining dimensionless items of influence factors according to the pi theorem, and deducing to obtain the limited wind speed u_cThe dimensionless calculation formula of (1); obtaining the numerical value of the smoke backflow length L of the fire under different working conditions through numerical simulation, obtaining the limited wind speed through the smoke backflow length, drawing the simulation result into a scatter diagram, and determining the influence factors on the limited wind speed u_cThe influence of (c); performing data fitting on the result to obtain the value of each unknown coefficient in the dimensionless relational expression, and further establishing the dimensionless limited wind speed u_cThe calculation formula of (2). The method has the advantages of being simple, suitable for different tunnels, greatly influencing the efficient utilization of the smoke exhaust capacity of the tunnels and providing guidance for fire smoke control and fire rescue of the side key smoke exhaust tunnels.

Description

A calculation method and application of limited wind speed for key smoke exhaust on the side of tunnel

technical field

The invention relates to the technical field of tunnel fire smoke control, in particular to a calculation method and application of a limited wind speed for key smoke exhaust at the side of a tunnel.

Background technique

Fire is one of the greatest risks to tunnel operations. Compared with ordinary ground buildings, tunnels have unique spatial structure and fire characteristics due to the narrow and closed characteristics of tunnels. In the event of a fire in the tunnel, the smoke cannot be discharged in time, which will easily cause suffocation or poisoning of people. If the vehicles in the tunnel are too late to leave, secondary injuries will occur, resulting in major catastrophic accidents involving mass deaths and injuries. Controlling the limited wind speed is conducive to the efficient use of the smoke exhaust capacity of the tunnel, and the smoke is controlled within a certain range to ensure personnel evacuation and rescue.

The definition of the restricted wind speed _uc in the tunnel fire scenario: the minimum longitudinal induced wind speed corresponding to the flue gas reverse flow length is not sensitive to the fluctuating exhaust flow velocity is called the restricted wind speed _uc , and the flue gas reverse flow length refers to the fire source traveling in the tunnel. The distance from the exhaust port in the direction, as shown in Figure 2, the limited wind speed u _c is the appropriate wind speed to ensure that the length of the reverse flow of the flue gas does not increase due to the decrease of the flow rate of the exhaust port. index. The current research mainly explores the calculation method of the critical wind speed. The critical wind speed is the longitudinal wind speed that just makes the counterflow length of the flue gas zero, which can ensure that there is no flue gas upstream of the fire source, but the critical wind speed is used to control the spread of the flue gas. On the one hand, due to the critical wind speed Theoretically, it is greater than the limited wind speed, so the smoke cannot be exhausted to the nearest upstream smoke outlet; The heat release rate of the fire source and the distance between the dimensionless smoke outlet and the fire source are related. Therefore, the longitudinal wind speed predicted by the critical wind speed model to control the reverse flow of the flue gas is still affected by the change of the smoke exhaust volume.

At present, most of the existing limited wind speed calculation methods are aimed at the situation where the smoke exhaust port is located at the top of the tunnel. The mouth is located on the side wall of the tunnel. Compared with the smoke exhaust at the top, the stress state and motion state of the smoke have changed at this time. There is no calculation method for the limited wind speed of the tunnel fire in the key smoke exhaust mode at home and abroad.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a calculation method and application of the limited wind speed of the key smoke exhaust fire at the side of the tunnel, aiming at solving the above technical problems.

The technical scheme that the present invention solves the above-mentioned technical problems is as follows:

A method for calculating the limited wind speed of a key smoke exhaust fire at the side of a tunnel, comprising the following specific steps:

S1: Determine the influencing factors of the limited wind speed uc in the tunnel fire scenario, and establish the relationship between the limited wind speed uc and the influencing factors: _f ( _uc ,Q,ρ ₀ , _{C P} ,T ₀ ,g , _HD )=0;

The influencing factors include fire source heat release rate Q, air density ρ ₀ , air constant pressure specific heat C _p , air temperature T ₀ , gravitational acceleration g, tunnel height H _D , the number of physical parameters n is 7, and the fire source heat The unit of release rate Q is kg.m ² /s ³ , the unit of air density ρ ₀ is kg/m ³ , the unit of air constant pressure specific heat C _p is m ² /s ² .K, the unit of air temperature T ₀ is K, the unit of gravitational acceleration g is m/ _s ² , and the unit of tunnel height HD is m;

S2: Determine a basic dimension according to the unit of the influencing factor, represent the influencing factor by the basic dimension, and establish a dimensional relationship between the limited wind speed _uc and the influencing factor;

S3: Determine a basic dimension according to the unit of the influencing factor, represent the influencing factor by the basic dimension, and establish a dimensional relationship between the limited wind speed _uc and the influencing factor;

In the step S3, the basic dimension includes mass M, time t, length L, and temperature T, and the basic dimension number η is 4;

In the step S3, the relationship between the limited wind speed _uc and the influencing factors is:

f(Lt ^-1 , ML ² t ^-3 , ML ^-3 , L ² t ^-2 T ^-1 , T, Lt ^-2 , L)=0;

S4: Determine the basic physical quantity of the influencing factor, obtain the number of dimensionless parameters of the influencing factor according to the π theorem as n-η=3, and then select the one directly related to the length L according to the selection principle of the circulation quantity in the π theorem Variable H _D , select the variable T ₀ directly related to the temperature T, select the variable g directly related to the time t, select the variable ρ ₀ directly related to the mass M, as the circulation amount, use these 4 circulation amounts and other n- All other parameters in the n physical parameters are sequentially combined into dimensionless parameters Π ₁ , Π ₂ , Π ₃ , the relational expression in the step S3 is converted into a dimensionless relational expression, and then the restricted wind speed u is obtained. The dimensionless calculation formula of _c ;

In the step S4, the dimensionless parameters Π ₁ , Π ₂ , and Π ₃ of the influencing factors are:

The dimensionless calculation formula of the restricted wind speed u _c is:

u_c ^*为无量纲风速，Q^**为无量纲功率；which is

u _c ^* is the dimensionless wind speed, Q ^** is the dimensionless power;

S5: FDS numerical simulation part: establish a scaled geometric model of the tunnel, set the virtual fire source as propane combustion, simulate different heat release rates of the fire source, set the flow velocity v of the exhaust port to gradually increase from small to large, and get the FDS software fitting When the flue gas counterflow length L decreases slowly with the increase of the flue gas flow velocity v, the induced wind speed generated in the tunnel by the flue gas flow velocity v at this time is the fire condition The value of the actual restricted wind speed _uc at the lower end of the tunnel, and the values of the influencing factors of the restricted wind speed _uc are measured and recorded. One side wall in the tunnel is provided with two smoke exhaust ports along the longitudinal direction, the The fire source is located on the center line of the one-way three-lane middle lane, and the steady-state fire or t-square fire is used. In the scaled geometric model, there are multiple temperature uniform intervals along the longitudinal direction of the top wall. Measuring points, extract the influencing factors of the restricted wind speed _uc fitted by the FDS software, a section of the scaled geometric model is provided with a plurality of flow velocity measuring points, and extract the restricted wind speed uc fitted by the _FDS software;

S6: Entity simulation: establish a scaled geometric model of the tunnel, and set different fire conditions in the scaled geometric model, including using the burner as the fire source, simulating different heat release rates of the fire source, and setting different flow velocity v of the exhaust port , and used to control different flue gas counterflow lengths L, and change the vertical wind speed under the fire conditions, and observe the moment when the flue gas counterflow length is not affected by the flow velocity of the exhaust port, and measure the actual restricted wind speed u _c at this moment. The numerical value, and the numerical value of the influencing factors of the restricted wind speed _uc are measured and recorded. There are two smoke exhaust ports on one side wall in the tunnel along the longitudinal direction, and the fire source is arranged between the two smoke exhaust ports. To the center line of the middle lane of the three lanes, a plurality of temperature sensors are installed at uniform intervals along the longitudinal direction of the top wall in the scaled geometric model to measure the influencing factors of the restricted wind speed _uc . An anemometer is installed on one section to measure the restricted wind speed u _c ;

S7: According to the values of the restricted wind speed _uc and the influencing factors under different fire conditions obtained in steps S5 and S6, respectively, draw the simulation results into scatter plots. If the fitted line graphs are similar, select the scatter plot obtained in step 5. perform data fitting;

S8: perform data fitting on the result scatter of the scatter diagram obtained in step 5, obtain the value of the unknown coefficient k ₂ in the dimensionless calculation formula in step S4, and set the obtained u _c ^* = k The calculated value of ₁ Q ^** is drawn into a scatter plot and data fitting is performed to obtain the value of the unknown coefficient k ₁ in the dimensionless calculation formula in the step S4, and then establish the limit of the dimensionless formula. The calculation formula of wind speed u _c :

On the basis of the above technical solutions, the present invention can also be improved as follows.

Further, an application of the method for calculating the limited wind speed of key smoke exhausting at the side of the tunnel includes the following steps:

Step 1. According to the calculation formula L ^* =76(v ^* ) ^-1.67 (Q ^* ) ^0.56 (l ^* )- ^0.23 and the obtained fire information: Q, _ρ0 , _{C p} , _{T 0} , g, HD , L, l, WD calculate the length L of the backflow of smoke in the fire tunnel, L ^* =L/ _HD , l ^* =l/ _HD , Q ^* =Q/ (H _D ^3/2 g ^1/2 W _D T ₀ C _p ρ ₀ ), v ^* is the dimensionless smoke exhaust rate, where W _D is the tunnel width, v is the flow velocity of the exhaust port, and l is the exhaust port to the fire source spacing;

Step 2. If L is greater than 1, calculate the limited wind speed u _c for key smoke exhaust on the side of the tunnel, and make the fans in the station halls at both ends of the accident section of the tunnel exhaust air to the accident section at the same time to form longitudinal wind, and make the velocity of the longitudinal wind greater than u _c , until the temperature sensor in the tunnel or the CO alarm detects that the flue gas counterflow length L=l, and then reduce the flow velocity of the longitudinal wind to u _c ;

Step 3. If the wind discharged by the fans in the station halls at both ends of the tunnel accident section makes L less than l, reduce the flow rate of the longitudinal wind to less than uc until the length of the countercurrent flow of the flue gas L= _l , and then increase the flow rate of the longitudinal wind to u _c .

Compared with the prior art, the beneficial effects of the present invention are:

The method is simple, and the parameters can be set according to the actual conditions of the tunnel, and it is suitable for different tunnels with side-focused smoke exhaust methods. The method is scientific and effective, applying the π theorem and dimensional analysis, and has a more theoretical basis. There is no calculation method for the restricted wind speed in the side-focused smoke exhaust mode. In this method, the main influencing factors of the heat release rate of the fire source are considered in the process of derivation of the dimensional relationship, and the obtained results have innovative and practical engineering significance. The limited wind speed of tunnel fire has a great impact on the efficient utilization of tunnel smoke exhaust capacity. Predicting and calculating the limited wind speed of tunnel fire can provide guidance for fire rescue in tunnel fire under the key smoke exhaust on the side.

Description of drawings

Fig. 1 is the flow chart of the calculation method of the limited wind speed of key smoke exhausting at the side of the tunnel of the present invention;

FIG. 2 is a schematic diagram of the limited wind speed in the side key smoke exhaust mode of the present invention;

3 is a schematic diagram of a reduced-scale model tunnel established in the present invention;

Fig. 4 is the relation diagram of restricted wind speed and fire source heat release rate in the present invention;

Fig. 5 is the numerical simulation result diagram of restricted wind speed in the present invention;

Figure 6 is a cross-sectional view of the induced wind speed directly measured by the Velocity measuring point of the FDS software.

In the accompanying drawings, the parts list represented by each number is as follows:

1. One-way three-lane tunnel, 2. Smoke outlet, 3. Temperature measuring point, 4. Flow velocity measuring point.

Detailed ways

The principles and features of the present invention will be described below with reference to the accompanying drawings and specific embodiments. The examples are only used to explain the present invention, but not to limit the scope of the present invention.

As shown in Figures 1 to 5, the present invention provides a method for calculating the limited wind speed of a key smoke exhaust fire on the side of a tunnel, comprising the following specific steps:

S1: Determine the definition of the restricted wind speed u _c in the tunnel fire scenario: the minimum longitudinal induced wind speed corresponding to the flue gas backflow length is not sensitive to the fluctuating flue gas flow velocity is called the restricted wind speed _uc , and the flue gas backflow length refers to the fire source The distance from the exhaust port in the direction of travel of the tunnel.

S2: Determine the influencing factors of the limited wind speed uc in the tunnel fire scenario, and establish the relationship between the limited wind speed uc and the influencing factors: _f ( _uc ,Q,ρ ₀ , _{C P} ,T ₀ ,g , _HD )=0;

The influencing factors include fire source heat release rate Q, air density ρ ₀ , air constant pressure specific heat C _p , air temperature T ₀ , gravitational acceleration g, tunnel height H _D , the number of physical parameters n is 7, and the fire source heat The unit of release rate Q is kg.m ² /s ³ , the unit of air density ρ ₀ is kg/m ³ , the unit of air constant pressure specific heat C _p is m ² /s ² .K, the unit of air temperature T ₀ is K, the unit of gravitational acceleration g is m/ _s ² , and the unit of tunnel height HD is m.

S3: Determine a basic dimension according to the unit of the influencing factor, represent the influencing factor by the basic dimension, and establish a dimensional relationship between the limited wind speed _uc and the influencing factor;

In the step S3, the basic dimension includes mass M, time t, length L, and temperature T, and the basic dimension number η is 4;

In the step S3, the relationship between the limited wind speed _uc and the influencing factors is:

f(Lt ^-1 , ML ² t ^-3 , ML ^-3 , L ² t ^-2 T ^-1 , T, Lt ^-2 , L)=0;

S4: Determine the basic physical quantity of the influencing factor, obtain the number of dimensionless parameters of the influencing factor according to the π theorem as n-η=3, and then select the one directly related to the length L according to the selection principle of the circulation quantity in the π theorem Variable H _D , select the variable T ₀ directly related to the temperature T, select the variable g directly related to the time t, select the variable ρ ₀ directly related to the mass M, as the circulation amount, use these 4 circulation amounts and other n- All other parameters in the n physical parameters are sequentially combined into dimensionless parameters Π ₁ , Π ₂ , Π ₃ , the relational expression in the step S3 is converted into a dimensionless relational expression, and then the restricted wind speed u is obtained. The dimensionless calculation formula of _c ;

In the step S4, the dimensionless parameters Π ₁ , Π ₂ , and Π ₃ of the influencing factors are:

The dimensionless calculation formula of the restricted wind speed u _c is:

u_c ^*为无量纲风速，Q^**为无量纲功率；which is

u _c ^* is the dimensionless wind speed, Q ^** is the dimensionless power;

S5: FDS numerical simulation part: establish a scaled geometric model of the tunnel, set the virtual fire source as propane combustion, and simulate the heat release rate of different fire sources. The size of the exhaust port is 0.3m×0.1m, and the flow velocity v of the exhaust port is set to gradually increase from small to large, and the different flue gas counterflow lengths L fitted by the FDS software are obtained. When the trend of increasing and decreasing becomes slow, the induced wind speed in the tunnel generated by the flow velocity v of the exhaust vent at this time is the value of the actual restricted wind speed _uc under the fire condition, and the influence of the restricted wind speed _uc is measured and recorded. The numerical value of the factor, the scaled geometric model of the tunnel is scaled at 1:10, and the dimensions are length × width × height 50m × 1.1m × 0.45m; There are two smoke exhaust ports 2, and the fire source is arranged between the two smoke exhaust ports. The fire source is located on the center line of the middle lane of the one-way three-lane. Steady-state fire or t-square fire is adopted, and the size is 0.6m × 0.2 m; the power of the fire source is 9.5-94.9kW, the corresponding heat release rate of the full-scale fire source is 3-30MW, and the scaled geometric model is provided with a plurality of temperatures evenly spaced along the longitudinal direction of the top wall Measuring points, extract the influencing factors of the restricted wind speed _uc fitted by the FDS software, a section of the scaled geometric model is provided with a plurality of flow velocity measuring points, and extract the restricted wind speed uc fitted by the _FDS software;

S5: Entity experiment part: establish a scaled geometric model of the tunnel, and set different fire conditions in the scaled geometric model, including using the burner as the fire source to simulate different heat release rates of the fire source. The size of the exhaust port is 0.3m×0.1m, and different flow velocity v of the exhaust port is set to control the length L of the reverse flow of the flue gas, and change the size of the longitudinal wind speed under the fire conditions, and observe that the length of the reverse flow of the flue gas is not affected. At the moment when the flow velocity of the exhaust port is affected, measure the value of the actual restricted wind speed _uc at that moment, and measure and record the value of the influencing factors of the restricted wind speed _uc . The scaled geometric model of the tunnel is scaled at 1:10, and the size is The length×width×height is 10m×1.1m×0.45m; one side wall of the one-way three-lane tunnel 1 is provided with two smoke exhaust ports 2 along the longitudinal direction, and the fire source is arranged between the two smoke exhaust ports. The fire source is located on the center line of the one-way three-lane middle lane, with a size of 15cm×15cm in length and width; the power of the fire source is 9.5-94.9kW, and the corresponding full-size fire source heat release rate is 3-30MW. In the scaled geometric model, a plurality of temperature sensors are installed at uniform intervals along the longitudinal direction of the top wall to measure the influencing factors of the limited wind speed u _c . An anemometer is installed on a section of the scaled geometric model, and the measurement is limited wind speed u _c ;

S6: According to the numerical values of the restricted wind speed _uc and the influencing factors under different fire conditions obtained in step S5, the simulation results are drawn into a scatter diagram;

S7: Perform nonlinear fitting on the resulting scatter points of all scatter plots, obtain the values of the unknown coefficients k ₁ and k ₂ in the dimensionless calculation formula in the step S4, and then establish a dimensionless formula The calculation formula of the restricted wind speed _uc :

The above-mentioned fire dynamic simulation software (FDS) is the prior art.

In step S5, in the FDS numerical simulation part, the one-way three-lane tunnel 1 is a 1:10 reduced size length × width × height of 50m × 1.1m × 0.45m; one side wall of the one-way three-lane tunnel 1 is provided with The two smoke exhaust ports 2 are provided with a plurality of temperature measuring points 3 evenly spaced on the inner top wall thereof, and a plurality of flow velocity measuring points 4 are arranged on a certain section of the tunnel.

In step S5, in the physical experiment part, the one-way three-lane tunnel 1 is a 1:10 reduced size length × width × height of 10m × 1.1m × 0.45m; one side wall of the one-way three-lane tunnel 1 is provided with two There are a number of smoke exhaust ports 2, and a plurality of temperature measuring points 3 are evenly spaced on the inner top wall, and a plurality of flow velocity measuring points 4 are arranged on a certain section of the tunnel. A k-type thermocouple with a diameter of 1mm and a probe of 0.1m is installed in a conceivable way. Each thermocouple sensor is connected to a 32-channel paperless recorder through a line. The temperature signal is sent to the controller, and the controller receives the corresponding temperature signal and stores it. Each flow velocity measuring point 4 is installed with a flow velocity measuring point in a way that those skilled in the art can think of. A hot-wire anemometer of the model (Anemomaster KA23) is used to detect the wind speed at the corresponding flow velocity measuring point 4, and the corresponding wind speed signal is sent. To the controller, the controller receives the corresponding flow rate signal and stores it. The above-mentioned controller, temperature sensor and wind speed sensor all adopt the prior art, and the control circuit between each temperature sensor, wind speed sensor and the controller is also the prior art. On the basis of the above conditions, the values of the heat release rate of the fire source and the flow rate of the smoke exhaust port are changed in turn to form different flue gas backflow lengths. Under different fire conditions, the restricted wind speed values under different fire conditions were obtained by changing the longitudinal wind speed observation and measurement. The specific simulation results are shown in Table 1:

Table 1 FDS numerical simulation results:

The simulation process takes the first group as an example: when the first group Q=9.5kW, the flue gas flow velocity changed is 3m/s to 11m/s, and finally the length of the flue gas counterflow is reduced from 5.95m to 0.75m. This decrease It is found that when the flue gas counterflow length reaches 1.05m/s, and the flow velocity of the exhaust port is increased again, the flue gas counterflow length L decreases very slowly and becomes insensitive. Then the flow rate of the smoke outlet corresponding to this 1.05m is 8m/s. Because the flow rate of the smoke outlet is 8m/s, an induced wind speed will be generated at both ends of the accident tunnel. The value of this induced wind speed is the restricted wind speed corresponding to Q=9.5kW , the induced wind speed value of 0.51m/s is directly measured by the Velocity measuring point of FDS, which is shown in Figure 6. The simulation process for the remaining groups was similar.

Table 2 Entity experimental results:

Due to the limited experimental conditions, the actual tunnel is not long enough, so only a few sets of experiments with small fire source heat release rate can be done, and the maximum fan power in the experiment can only make the exhaust flow velocity reach 11m/s. So the whole experimental data is less. Also, because the experiment was in winter, there was a big difference between the numerical simulation and the ambient temperature in the laboratory, and the final experimental results were inaccurate with the FDS simulation results. The first group of experiments has a small error of multiple simulations, and the other groups of experiments have the same trend. This experiment verifies the correctness of the results of the FDS simulation. According to the numerical simulation results in Table 1 and Table 2, draw a scatter diagram to obtain the relationship between the restricted wind speed _uc and various influencing factors, as shown in Figure 4. The FDS simulation results and the physical experimental results have the same trend, so the obtained functions are similar :

Figure 4 is a graph showing the relationship between the restricted wind speed _uc and the fire source heat release rate Q. From Figure 4, it can be known that the restricted wind speed _uc first increases and then tends to be stable with the increase of the fire source heat release rate Q;

即0＜Q^**≤0.52时，k₂＝1；当Q^**＞0.52时，k₂＝0；Using Origin software to fit the data in Figure 4, the functional relationship between u _c ^* and Q ^** can be obtained as

That is, when 0<Q ^** ≤0.52, k ₂ =1; when Q ^** >0.52, k ₂ =0;

In order to determine the values of the coefficients k ₁ and k ₁ ' in the above formula, the calculated values of u _c ^* = k ₁ Q ^** are plotted in Fig. 5. It can be seen from Fig. 5 that the numerical simulation results fluctuate around a straight line, k ₁ is 0.34, the correlation coefficient is 0.99, and k ₁ ' is 0.4. It is shown that the numerical formula of the dimensionless confined wind speed u _c ^* is consistent with the numerical simulation results. Substituting k ₁ =0.34 into the above formula, the calculation formula of dimensionless restricted wind speed u _c ^* is:

In the formula: u _c ^* : Dimensionless confined wind speed, Q ^** : Dimensionless fire source heat release rate.

Through this method, the value of the limited wind speed under different heat release rates of the fire source can be quickly obtained.

The beneficial effect of the invention is that the parameters can be set according to the actual conditions of the tunnel, and it is suitable for different tunnels adopting the key smoke exhaust method on the side. The method is scientific and effective, applying theorems and dimensional analysis, and has a more theoretical basis. There is currently no calculation method for the dimensionless restricted wind speed u _c ^* in tunnel fires. This method considers the most important factor in the derivation of the dimension relationship, the heat release rate of the fire source, and the obtained results are innovative and of practical engineering significance. The limited wind speed of tunnel fire has a great impact on the efficient utilization of tunnel smoke exhaust capacity. Predicting and calculating the limited wind speed of tunnel fire can provide guidance for fire rescue in tunnel fire under the key smoke exhaust on the side.

An application of the calculation method for the limited wind speed of key smoke exhaust on the side of the tunnel,

Step 1. According to the calculation formula L ^* =76(v ^* ) ^-1.67 (Q ^* ) ^0.56 (l ^* )- ^0.23 and the obtained fire information: Q, ρ ₀ , _{C p} , _{T 0} , g, HD , L, l, WD calculate the length L of the backflow of smoke in the tunnel where the fire occurred, L ^* =L/ _HD , l ^* =l/ _HD , Q ^* =Q/( _HD ^3/2 g ^1/2 W _D T ₀ C _p ρ ₀ ), v ^* is the dimensionless smoke exhaust rate, v ^* =v/( _HD ^1/2 g ^1/2 ), where _WD is the width of the tunnel, v is the flow velocity of the exhaust port, and l is the distance from the exhaust port to the fire source;

Step 2. If L is greater than 1, calculate the limited wind speed u _c for key smoke exhaust on the side of the tunnel, and make the fans in the station halls at both ends of the accident section of the tunnel exhaust air to the accident section at the same time to form longitudinal wind, and make the velocity of the longitudinal wind greater than u _c , until the temperature sensor in the tunnel or the CO alarm detects that the flue gas counterflow length L=l, and then reduce the flow velocity of the longitudinal wind to u _c ;

Step 3. If the wind discharged by the fans in the station halls at both ends of the tunnel accident section makes L less than l, reduce the flow rate of the longitudinal wind to less than uc until the length of the countercurrent flow of the flue gas L= _l , and then increase the flow rate of the longitudinal wind to u _c .

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection of the present invention. within the range.

Claims (2)

1. A method for calculating the limited wind speed of a key smoke exhaust fire on the side of a tunnel, comprising the following specific steps: S1: Determine the influencing factors of the limited wind speed uc in the tunnel fire scenario, and establish the relationship between the limited wind speed uc and the influencing factors: _f ( _uc ,Q,ρ ₀ , _{C P} ,T ₀ ,g , _HD )=0; The influencing factors include fire source heat release rate Q, air density ρ ₀ , air constant pressure specific heat C _p , air temperature T ₀ , gravitational acceleration g, tunnel height H _D , the number of physical parameters n is 7, and the fire source heat The unit of release rate Q is kg.m ² /s ³ , the unit of air density ρ ₀ is kg/m ³ , the unit of air constant pressure specific heat C _p is m ² /s ² .K, the unit of air temperature T ₀ is K, the unit of gravitational acceleration g is m/ _s ² , and the unit of tunnel height HD is m; S2: Determine a basic dimension according to the unit of the influencing factor, represent the influencing factor by the basic dimension, and establish a dimensional relationship between the limited wind speed _uc and the influencing factor; S3: the basic dimension includes mass M, time t, length L, temperature T, and the basic dimension number η is 4; In the step S2, the relationship between the limited wind speed _uc and the influencing factor is: f(Lt ^-1 , ML ² t ^-3 , ML ^-3 , L ² t ^-2 T ^-1 , T, Lt ^-2 , L)=0; S4: Determine the basic physical quantity of the influencing factor, obtain the number of dimensionless parameters of the influencing factor according to the π theorem as n-η=3, and then select the one directly related to the length L according to the selection principle of the circulation quantity in the π theorem Variable H _D , select the variable T ₀ directly related to the temperature T, select the variable g directly related to the time t, select the variable ρ ₀ directly related to the mass M, as the circulation amount, use these 4 circulation amounts and other n- All other parameters in the n physical parameters are sequentially combined into dimensionless parameters Π ₁ , Π ₂ , Π ₃ , the relational expression in the step S3 is converted into a dimensionless relational expression, and then the restricted wind speed u is obtained. The dimensionless calculation formula of _c ; In the step S4, the dimensionless parameters Π ₁ , Π ₂ , and Π ₃ of the influencing factors are:

The dimensionless calculation formula of the restricted wind speed u _c is:

which is

u _c ^* is the dimensionless wind speed, Q ^** is the dimensionless power; S5: FDS numerical simulation part: establish the scaled geometric model of the tunnel, set the virtual fire source as propane combustion, simulate the heat release rate of different fire sources, set the flow velocity v of the exhaust port to increase gradually from small to large, and get the FDS software fitting When the flue gas counterflow length L decreases slowly with the increase of the flue gas flow velocity v, the induced wind speed generated in the tunnel by the flue gas flow velocity v at this time is the fire condition The value of the actual restricted wind speed _uc at the lower end of the tunnel, and the values of the influencing factors of the restricted wind speed _uc are measured and recorded. One side wall in the tunnel is provided with two smoke exhaust ports along the longitudinal direction, the The fire source is located on the center line of the one-way three-lane middle lane, and the steady-state fire or t-square fire is used. In the scaled geometric model, there are multiple temperature uniform intervals along the longitudinal direction of the top wall. Measuring points, extract the influencing factors of the restricted wind speed _uc fitted by the FDS software, a section of the scaled geometric model is provided with a plurality of flow velocity measuring points, and extract the restricted wind speed uc fitted by the _FDS software; S6: Entity simulation: establish a scaled geometric model of the tunnel, and set different fire conditions in the scaled geometric model, including using the burner as the fire source, simulating different heat release rates of the fire source, and setting different smoke exhaust flow velocity v , and used to control different flue gas counterflow lengths L, and change the vertical wind speed under the fire conditions, and observe the moment when the flue gas counterflow length is not affected by the flow velocity of the exhaust port, and measure the actual restricted wind speed u _c at this moment. The numerical value, and the numerical value of the influencing factors of the restricted wind speed _uc are measured and recorded. There are two smoke exhaust ports on one side wall in the tunnel along the longitudinal direction, and the fire source is arranged between the two smoke exhaust ports. To the center line of the middle lane of the three lanes, a plurality of temperature sensors are installed at uniform intervals along the longitudinal direction of the top wall in the scaled geometric model to measure the influencing factors of the restricted wind speed _uc . An anemometer is installed on one section to measure the restricted wind speed u _c ; S7: According to the values of the restricted wind speed _uc and the influencing factors under different fire conditions obtained in steps S5 and S6, respectively, draw the simulation results into scatter plots. If the fitted line graphs are similar, select the scatter plot obtained in step 5. perform data fitting; S8: Perform data fitting on the resulting scatter points of all the scatter plots obtained in step 5, and obtain the value of the unknown coefficient k ₂ in the dimensionless calculation formula in the step S4.

Draw a scatter plot of the calculated value and perform data fitting to obtain the value of the unknown coefficient k ₁ in the dimensionless calculation formula in the step S4, and then establish the dimensionless formula of the restricted wind speed u _c Calculation formula:

2. the application of the calculation method of the key smoke exhaust restricted wind speed of the tunnel side as claimed in claim 1, comprises the following steps: Step 1. According to the calculation formula L ^* =76(v ^* ) ^-1.67 (Q ^* ) ^0.56 (l ^* )- ^0.23 and the obtained fire information: Q, _ρ0 , _{C p} , _{T 0} , g, HD , L, l, WD calculate the length L of the backflow of smoke in the fire tunnel, L ^* =L/ _HD , l ^* =l/ _HD , Q ^* =Q/ (H _D ^3/2 g ^1/2 W _D T ₀ C _p ρ ₀ ), v ^* is the dimensionless smoke exhaust rate, where W _D is the tunnel width, v is the flow velocity of the exhaust port, and l is the exhaust port to the fire source spacing; Step 2. If L is greater than 1, calculate the limited wind speed u _c for key smoke exhaust on the side of the tunnel, and make the fans in the station halls at both ends of the accident section of the tunnel exhaust air to the accident section at the same time to form longitudinal wind, and make the velocity of the longitudinal wind greater than u _c , until the temperature sensor in the tunnel or the CO alarm detects that the flue gas counterflow length L=l, and then reduce the flow velocity of the longitudinal wind to u _c ; Step 3. If the wind discharged by the fans in the station halls at both ends of the tunnel accident section makes L less than l, reduce the flow rate of the longitudinal wind to less than uc until the length of the countercurrent flow of the flue gas L= _l , and then increase the flow rate of the longitudinal wind to u _c .

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