Influence of tunnel width on longitudinal smoke control

The objective is to carry out experiments on scale models and CFD calculations in order to study the influence of tunnel width Won critical velocity (for a given tunnel height H). By definition, the critical velocity is the minimum longitudinal velocity needed to prevent smoke back flow when a fire occurs in a tunnel. Two different experimental reduced scale models are used: the first one is a thermal model using a propane gas flame to simulate the fire and the second one is a densimetrical model in which the fire-induced-smoke is represented by a continuous release of an isothermal buoyant mixing. In both approaches, for aspect ratios W/H greater than unity, it is noticed that the critical velocity decreases when the width increases, as predicted by theory, but for low values of the aspect ratio (i.e. when W<H) and for high enough fire heat release rates, the critical velocity significantly increases with tunnel width. This can be associated to a change in the transverse flow pattern close to the buoyant source. Complementary CFD calculations are also presented in order to describe the influence of the lateral confinement on smoke plume spreading and then, on critical velocity. (C) 2006 Elsevier Ltd. All rights reserved.