Interpretation of flow fields induced by water spray systems in reduced-scale tunnel fire experiments by means of CFD simulations

Abstract

Computational Fluid Dynamics (CFD) simulation results, obtained with FDS 6.0.1 (McGrattan et al., 2013), are presented of reduced-scale tunnel fire tests. In (Sun et al., 2016), an extensive data set has been discussed in terms of temperature measurements in a reduced-scale tunnel, involving longitudinal ventilation and a variety of water supply through nozzles, in the context of potential smoke blockage. In (Sun et al., 2016), 10 different scenarios have been discussed, for different numbers of nozzles and different nozzle configurations. Given the limitation of the experimental instrumentation, as a series of thermocouple trees, a full interpretation of the flow field was impossible. Nevertheless, a detailed characterization and interpretation of this turbulent flow field under different circumstances is essential in the discussion of potential smoke blockage. To that purpose, CFD can be a very useful tool. In this paper, as a first step, results are presented for 2 cases, without mechanical longitudinal ventilation, in order to illustrate the validity and potential of the CFD simulations, with and without the water system (4 nozzles) activated. The validity of the CFD results, using the default FDS settings for turbulence and combustion modeling, is illustrated first through comparison of the temperature profiles with the experimental data. A comprehensive sensitivity study on the computational mesh and model settings for the water sprays is included. Subsequently, the mean flow and temperature fields are analyzed, providing significant additional insight into the impact of the water system. The entrainment, induced by the water sprays, is illustrated. This causes downward motion of the smoke in the sprays. By bumping onto each other, the impinging flows onto the floor in their turn create an upward flow in between the water spray envelopes that impinges onto the ceiling in the absence of longitudinal ventilation. The global effect is smoke blockage by the water system.

Analysis of the Fire Propagation in a Sublevel Coal Mine

“…Many measures have been studied following the statements from the two previous paragraphs. Analyzing the best evacuation routes [36], the usage of airflow reversal [37], applying different techniques to extinguish the fire [15] such as foam [38,39], or recasting the traditional sealing method [23] into a new dynamic seal [40]. Other approaches, like the determination of the limit conditions for firefighters [12] or early detection systems [41] have also been proposed.…”

“…There are some interesting studies in small scale tunnels currently. Guo and Zhang [11] have compared experimental data from a fire developed in a very narrow tunnel with CFD analysis, while Sun et al [15] have studied the effectiveness of a water spray system to extinguish the fire. Full-scale tests have been done over the last decades [16,17], but only a few real-scale fire studies have compared modeled data with actual measurements [18][19][20], with a lack of studies focused on a long period of time in an ongoing mine.…”

Numerical Simulations on the Extinguishing Effect of Water Mist System with Different Parameters of Longitudinal Ventilation in Curve Tunnel Fire

“…For a 30 MW fire, the value of D * is about 3.66 m. is means that a mesh size of 0.36 m or less should provide reliable results. To obtain the proper grid sizes, grid sensitivity analyses are carried out as in the previous studies [17]. e grid sizes of 0.2 m, 0.25 m, and 0.5 m are selected in the current work.…”

“…Current research mostly focuses on exploring the influence of longitudinal ventilation in linear highway tunnels on water mist fire extinguishing [17][18][19].…”

The combined effect of a water mist system and longitudinal ventilation on the fire and smoke dynamics in a tunnel

“…The ratio of the water mist momentum to the smoke momentum is calculated for both tests in [9], with the obviously higher values in [8] than [9], therefore different results in terms of blocking efficiency were obtained. Sun et al [10] reproduced the experiments in [8] and visualized the entrainment mechanism of the smoke by the water mists with the aid of FDS. It could be observed that due to the spray-induced impinging jets onto the floor, there appeared a clear upward flow motion between the nozzles, acting as a 'barrier' to block the smoke spread.…”