Numerical Simulation and Analysis of Critical Velocity in Tunnel Fires Based on FDS

2013 ◽  
Vol 831 ◽  
pp. 455-459
Author(s):  
Shu Hui Xu ◽  
Ling Fei Cui ◽  
Lei Ning ◽  
Zi Ye Wang
Keyword(s):  
Heat Release ◽  
Critical Velocity ◽  
Heat Release Rate ◽  
Release Rate ◽  
Small Scale ◽  
Smoke Control ◽  
Tunnel Fires ◽  
Tunnel Fire ◽  
Velocity Prediction ◽  
The One

Critical velocity is a very important parameter in smoke control of tunnel fires and the variation of critical velocity against fire heat release rate is also one of the most important issues in tunnel fire researches. In this paper, a simplified physical model of a tunnel was established and the predictions of critical velocity for fire sizes in the 5-100MW range were carried out by FDS simulations. The FDS-predicted dimensionless critical velocities were compared with the values calculated by Wu and Bakar’s model. The result indicated that when the heat release rate was relatively small, Q≤30MW, the critical velocity increased with the increasing of heat release rate and varied as the one-third power of the heat release rate; when Q≥40MW, the growth rate of critical velocity became very small; after Q reach to 60MW, the critical velocity was almost unchanged with the increasing of heat release rate. In addition, the values of critical velocity calculated by Wu and Bakar’model which was derived from small-scale gas fire tests were underestimated. Therefore, the model suggested by Wu and Bakar is not suitable for critical velocity prediction in tunnel fires.

scholarly journals Numerical Investigation of Critical Velocity in Reduced Scale Tunnel Fire with Constant Heat Release Rate

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Ruben Mouangue ◽  
Philippe M. Onguene ◽  
Justin T. Zaida ◽  
Henri P. F. Ekobena
Keyword(s):  
Heat Release ◽  
Critical Velocity ◽  
Heat Release Rate ◽  
Release Rate ◽  
Combustion Products ◽  
Healthy Environment ◽  
Tunnel Fire ◽  
Air Supply ◽  
Minimum Velocity ◽  
Reduced Scale

When a fire occurs in a tunnel in the absence of sufficient air supply, large quantities of smoke are generated, filling the vehicles and any space available around them. Hot gases and smoke produced by fire form layers flowing towards extremities of the tunnel which may interfere with person’s evacuation and firefighter’s intervention. This paper carries out a numerical simulation of an unexpected fire occurring in a one-way tunnel in order to investigate for the critical velocity of the ventilation airflow; this one is defined as the minimum velocity able to maintain the combustion products in the downstream side of tunnel. The computation is performed successively with two types of fuels representing a large and a small heat release rate, owing to an open source CFD code called ISIS, which is specific to fires in confined and nonconfined environments. It is indicated that, after several computations of full-scale fires of 43.103 and 19.103 kJ/kg as heat release rate, the velocities satisfying the criterion of healthy environment in the upstream side of the tunnel are 1.34 m/s and 1.12 m/s, respectively.

Effects of ambient pressure on the critical velocity and back-layering length in longitudinal ventilated tunnel fire

2019 ◽  
Vol 29 (7) ◽  
pp. 1017-1027
Author(s):  
Guanfeng Yan ◽  
Mingnian Wang ◽  
Li Yu ◽  
Yuan Tian
Keyword(s):  
Heat Release ◽  
High Altitude ◽  
Critical Velocity ◽  
Heat Release Rate ◽  
Release Rate ◽  
Ambient Pressure ◽  
Smoke Movement ◽  
Tunnel Fire ◽  
Longitudinal Ventilation ◽  
High Altitude Area

Nowadays, the critical velocity and back-layering length are the key parameters in longitudinal ventilation design. However, most studies research them at standard air pressure but ambient pressure decreases at high-altitude area and the reduced ambient pressure could affect the smoke movement characteristics in a tunnel fire. In order to investigate the effect of ambient pressure on the velocity and back-layering length in longitudinal ventilated tunnel, theoretical analysis was carried out first and a series of numerical simulation were conducted with varying heat release rate and ambient pressure. Results show that Li’s model is also reliable under various ambient pressures. The critical velocity under various ambient pressures would become larger with an increase in the heat release rate and would remain stable after the heat release rate reaches a certain value. At smaller heat release rate, the length of counterflow would be higher under reduced ambient pressure while it remains the same when the HRR is large. This could provide reference for tunnel ventilation design at high-altitude areas.

Scale Modeling on the Effect of Air Velocity on Heat Release Rate in Tunnel Fire

2008 ◽  
Vol 18 (2) ◽  
pp. 111-124 ◽  
Author(s):  
C. Chen ◽  
L. Qu ◽  
Y. X. Yang ◽  
G. Q. Kang ◽  
W. K. Chow
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Air Velocity ◽  
Tunnel Fire ◽  
Scale Modeling

Flame Area Fluctuation Measurements in Velocity-Forced Premixed Gas Turbine Flames

2015 ◽  
Author(s):  
Alexander J. De Rosa ◽  
Janith Samarasinghe ◽  
Stephen J. Peluso ◽  
Bryan D. Quay ◽  
Domenic A. Santavicca
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Heat Release Rate ◽  
Release Rate ◽  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Small Scale ◽  
Flame Velocity ◽  
Unstable Combustion

Fluctuations in the heat release rate that occur during unstable combustion in lean premixed gas turbine combustors can be attributed to velocity and equivalence ratio fluctuations. For a fully premixed flame, velocity fluctuations affect the heat release rate primarily by inducing changes in the flame area. In this paper, a technique to analyze changes in flame area using chemiluminescence-based flame images is presented. The technique decomposes the flame area into separate components which characterize the relative contributions of area fluctuations in the large scale structure and the small scale wrinkling of the flame. The fluctuation in the wrinkled area of the flame which forms the flame brush is seen to dominate its response in the majority of cases tested. Analysis of the flame area associated with the large scale structure of the flame resolves convective perturbations that move along the mean flame position. Results are presented that demonstrate the application of this technique to both single-nozzle and multi-nozzle flames.

scholarly journals Research on the maximum fire smoke temperature beneath tunnel ceilings using longitudinal ventilation

2018 ◽  
Vol 251 ◽  
pp. 02020
Author(s):  
Hui Yang ◽  
Bingyan Dong ◽  
Sijian Zhang ◽  
Dahui Sun ◽  
Kirill Lushin
Keyword(s):  
Numerical Simulation ◽  
Numerical Simulations ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Experimental Results ◽  
Small Scale ◽  
Longitudinal Ventilation ◽  
Fire Smoke

The maximum fire smoke temperature beneath tunnel ceilings using longitudinal ventilation was studied by both small-scale experiments and numerical simulations for a small heat release rate (HRR) fire. And then, the accuracy of the numerical simulation is verified. A numerical simulation is subsequently employed to modify the Kurioka model for cases in large HRR. Then, the modified Kurioka model is verified by various on-site high HRR fire experimental results conducted by other authors.

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