Control of smoke flow in tunnel fires using longitudinal ventilation systems - a study of the critical velocity

摘要

There are two uncertains in the current methods of prediction of the critical ventilation velocity which were mainly based on semi-empirical equations obtained from the Froude Number preservation combining with some experimental data. The first is the influence of the fire power on the critical ventilation velocity. The second is the effect of the tunnel geometry on the critical velocity. Both problems lead to the issues of the scaling techniques in the tunnel fires. This study addressed these problems by carrying out a series of experimental tests in five model tunnels having the same height but different cross-sectional geometry. Comprehensive CFD simulations have been carried out to examine the flow behaviour inside the tunnels. The study points out that the fire plum distribution inside the tunnel affects the relationship between the critical ventilation velocity and the fire heat release rate. The study used dimensionless velocity and dimensionless heat release rate with the tunnel hydraulic height (tunnel mean hydraulic diameter) as the characteristic length in the experimental data analysis. The new scaling techniques are examined by applying the scaling techniques to the present experimental results and three large-scale experimental results available in the public literatures.