*2.2. Ventilation Parameters*

Several factors should be fully considered in ventilation and smoke control in tunnels, such as the pressure of ventilation fans, on-way resistance, local resistance, and fire wind pressure. Among these, fire wind pressure *p<sup>f</sup>* [25], on-way resistance *p<sup>λ</sup>* and local resistance

*p<sup>ξ</sup>* are regarded as ventilation resistance in the design and calculation of the ventilation system, which can be expressed, respectively, as: 1 2 *i i i p v* = = The ventilation system in the tunnel satisfies the conservation of energy:

*i*

*L*

*D*

*i*

2

*Fire* **2022**, *5*, x FOR PEER REVIEW 3 of 10

of the ventilation system, which can be expressed, respectively, as:

*p*

*v*

*p*

*i*

*v*

= 

 *f*

 *p*

+

1

*n*

=

*i*

*i*

*n*

wind pressure. Among these, fire wind pressure

*p*

local resistance

where

*p*

$$p\_{\lambda} = \sum\_{i=1}^{n} \lambda\_i \frac{L\_i}{D\_i} \frac{\rho}{2} v\_i^2 \tag{4}$$

[25], on-way resistance

*p*

and

(4)

(5)

(6)

*v*

(7)

;

*f*

*f*

are regarded as ventilation resistance in the design and calculation

*p*

2

 *i*

 *v*

2

$$p\_{\tilde{\varsigma}} = \sum\_{i=1}^{n} \tilde{\varsigma}\_{i} \frac{\rho}{2} v\_{i}^{2} \tag{5}$$

The ventilation system in the tunnel satisfies the conservation of energy: at the fire location should exceed the critical longitudinal velocity *c* [8]:

$$p\_v + p\_f + p\_\lambda + p\_{\tilde{\xi}} = \frac{1}{2}\rho v\_i^2 \tag{6}$$

In order to meet the requirements of smoke control, the average wind velocity *v<sup>f</sup>* at the fire location should exceed the critical longitudinal velocity *v<sup>c</sup>* [8]: sure, (Pa); *f p* is fire wind pressure, (Pa); is frictional resistant coefficient; is local

$$
v\_f \ge v\_c \tag{7}$$

where *p<sup>λ</sup>* is on-way resistance, (Pa); *p<sup>ξ</sup>* is local resistance, (Pa); *p<sup>v</sup>* is ventilation pressure, (Pa); *p<sup>f</sup>* is fire wind pressure, (Pa); *λ* is frictional resistant coefficient; *ξ* is local resistance coefficient; *v<sup>i</sup>* is airflow velocity, (m/s); *v<sup>f</sup>* is airflow velocity of fire source location, (m/s). location, (m/s). **3. Numerical Simulation**

### **3. Numerical Simulation** In this paper, FDS (Version 6.5.3) codes are used for simulating smoke movement

*3.1. Model Design* induced by fire [26], which is developed by NIST. The fire tunnel model is based on the

*3.1. Model Design*

resistance coefficient;

In this paper, FDS (Version 6.5.3) codes are used for simulating smoke movement induced by fire [26], which is developed by NIST. The fire tunnel model is based on the Qiongzhou Strait shield tunnel in southern China, which consists of two main tunnels, one service tunnel and multiple cross passages, with a total length of 21 km. To simplify the model, three modules of the tunnel are considered: one main tunnel with a horseshoe section area of 55 m<sup>2</sup> and height of 8.5 m; one service tunnel with a section area of 42.8 m<sup>2</sup> ; and the cross passages. The total length of the tunnel model is 600 m. The ventilation section covers the whole section of the tunnel, as shown in Figure 1. The section shape is the ventilation space section. A series of temperature and velocity measuring points are arranged at a height of 2 m inside the main tunnel, service tunnel and cross passages, with 1 m interval longitudinally; the velocity and temperature slices are set along the tunnel plotted in Figure 1b. For a high-speed railway tunnel, the heat release rate of 20 MW for train fires is recommended by the 'Code for Design on Rescue Engineering for Disaster Prevention and Evacuation of Railway Tunnel' (TB 10020-2017) [27], which is selected for modeling. Qiongzhou Strait shield tunnel in southern China, which consists of two main tunnels, one service tunnel and multiple cross passages, with a total length of 21 km. To simplify the model, three modules of the tunnel are considered: one main tunnel with a horseshoe section area of 55 m<sup>2</sup> and height of 8.5 m; one service tunnel with a section area of 42.8 m<sup>2</sup> and the cross passages. The total length of the tunnel model is 600 m. The ventilation section covers the whole section of the tunnel, as shown in Figure 1. The section shape is the ventilation space section. A series of temperature and velocity measuring points are arranged at a height of 2 m inside the main tunnel, service tunnel and cross passages, with 1 m interval longitudinally; the velocity and temperature slices are set along the tunnel plotted in Figure 1b. For a high-speed railway tunnel, the heat release rate of 20 MW for train fires is recommended by the 'Code for Design on Rescue Engineering for Disaster Prevention and Evacuation of Railway Tunnel' (TB 10020-2017) [27], which is selected for modeling.

**Figure 1.** *Cont*.

**Cases No.**

**Location (m)**

**(m)**

**Figure 1.** Simulation model: (**a**) Top view; (**b**) Side view. **Figure 1.** Simulation model: (**a**) Top view; (**b**) Side view.
