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45
TABLE 8
OBJECTIVES OF ANALYTICAL FIRE MODELING FOR TUNNEL FIRE SAFETY
Means Use for Research Use for Design Use for Operation
Numerical Advantages: Advantages: Advantages:
Models (CFD) - Possibility to study - Possibility to get an - Possibility to describe
many different optimization by the use the physical conditions
situations of different in several locations of
- Information on flow assumptions the tunnel
structures unattainable Disadvantages: Disadvantages:
with other methods - The model requires - Theoretical results lead
Disadvantages: qualification to theoretical
- The conclusions must Conclusions: conclusions
be correlated to - Useful method for Conclusions:
existing experimental projects, if validated - The adaptation
references depends on the use of
Conclusions: the model
- Useful method for
research
Source: PIARC (21).
calculated results and measurements to define rules for run- SUMMARY
ning fire simulations. However, it may be able to fit all the
parameters without physical reasons because such calibration Theoretical models, especially computer-based models, can
could not be transposed to other configurations. be valuable in assisting tunnel fire safety decision making.
However, such models can also be misleading.
The international community has made large efforts and
investments in research programs on fire safety in tunnels Nowadays, CFD software is considered as the design tool
during the last decade. The number of international congresses of choice for obtaining an optimum design, because experi-
on this subject, the development of fire model and large fire mental methods are costly, complex, and yield limited infor-
test programs carried out in recent years in Europe and in the mation. However, it requires in-depth knowledge of physical
United States (Memorial Tunnel) confirm this tendency. processes and numerical models and, preferably, testing
experience from the numerical modeler.
The CFD codes are already largely used to study fire situ-
ations in tunnels; however, additional research and validation The CFD simulations of tunnel fires driven by buoyancy
works are required to ensure the validity of their results. forces with significant energy release require a solution of
the NavierStokes equations with appropriate boundary
Some research is required to improve existing models, conditions.
such as turbulence or combustion models. This research is
generally done by universities and laboratories, the activity Table 8 provides a summary of the objectives of analyti-
of which deals with fundamental fluid dynamics phenomena cal fire modeling for tunnel fire safety based on the literature
and development of CFD codes. review.
With the development of the sprinkler system application Many commercial CFD packages have been developed in
for road tunnels came the need to model its performance. recent years. Initially, the strengths, weaknesses, and limita-
Much research has been published on CFD modeling of tions of each program are investigated. Validation of the
sprinkler systems and water mist systems (3640); however, results against experimental data or another equivalent pro-
there is a need to validate the sprinkler models against full-scale gram is necessary in order to have accurate results. Most of
tunnel fire tests. Additional research is needed for numerical the commercially available CFD codes used in this synthesis
modeling of sprinkler system impacts on flame and fire size. report have been validated against some tests; however, at
times users try to stretch the software application to areas
The next step is to undertake new small- and large-scale where the applications have not been validated. For example,
experiments with the primary objective of validating and it is difficult to find a CFD program that has been validated
calibrating physical models. It may include understanding for sprinkler system application in full-scale tunnel tests. The
of flow generated by fire as well as measurements of some same applies to turbulent models; radiation models applied
physical smoke properties, which are critical for models for road tunnels. There is a need for additional tests and val-
(i.e., radiative smoke properties, generation of soot). idations of the CFD models for road tunnels.
