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ABSTRACT: This paper applies a novel and fast modelling approach to simulate tunnel ventilation flows during fires. The complexity and
high cost of full CFD models and the inaccuracies of simplistic zone or analytical models are avoided by efficiently combining
mono-dimensional (1D) and CFD (3D) modelling techniques. A simple 1D network approach is used to model tunnel regions where
the flow is fully developed (far field), and a detailed CFD representation is used where flow conditions require 3D resolution (near field). This multi-scale method has previously been applied to simulate tunnel ventilation systems including jet fans, vertical
shafts and portals (Colella et al., Build Environ 44(12): 2357–2367, 2009) and it is applied here to include the effect of
fire. Both direct and indirect coupling strategies are investigated and compared for steady state conditions. The methodology
has been applied to a modern tunnel of 7m diameter and 1.2km in length. Different fire scenarios ranging from 10MW to 100MW
are investigated with a variable number of operating jet fans. Comparison of cold flow cases with fire cases provides a quantification
of the fire throttling effect, which is seen to be large and to reduce the flow by more than 30% for a 100MW fire. Emphasis
has been given to the discussion of the different coupling procedures and the control of the numerical error. Compared to
the full CFD solution, the maximum flow field error can be reduced to less than few percents, but providing a reduction of
two orders of magnitude in computational time. The much lower computational cost is of great engineering value, especially
for parametric and sensitivity studies required in the design or assessment of ventilation and fire safety systems.
KeywordsTunnel–Ventilation systems–Multiscale modelling–CFD–Jet fans
Fire Technology 04/2012; 47(1):221-253. · 0.43 Impact Factor
