Extended CFD models for numerical simulation of tunnel fire under natural ventilation: Comparative analysis and experimental verification

Abstract

This paper proposed Air Entrainment Model (AEM) and Mass Transfer-Volumetric Heating Source model (MT-VHS). Then different physical models of tunnel, gas description models and combustion models were used. CFD results were compared with reduced scale experiments and previous theories. The results show that traditional numerical simulation on tunnel model may cause asymmetrical temperature profile, because the pressure of tunnel portal is always set to be constant. Expanded computational domain can avoid this unreasonable setting. Boussinesq approximation underestimates temperature profile under ceiling because it ignores the variation of air property with temperature. Fitting parameters of air properties are more reasonable. In terms of combustion model, Volumetric Heating Source (VHS) neglects the plume generation. Heat release rate by Eddy Dissipation (ED) is not stable because it is affected by turbulent mixing. The mass sink of AEM entrains not only fresh air but also hot smoke. So the temperature profile by AEM deviates from experimental data much. Maximum temperature, temperature profile under ceiling and smoke layer height predicted by MT-VHS is close to experimental data and theoretical predictions, especially when the heat convection between wall and hot smoke is considered.

Keywords

• Tunnel fire safety
• CFD models
• Numerical simulation
• Reduced-scale experiments
• Comparative analysis