Numerical Prediction of the Critical Velocity for Forced Ventilation Road Tunnel

Document Type : Original Article

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Egyptian Armed Forces.

Abstract

Abstract:
Reliable design of tunnel ventilation system requires knowledge of fire-induced smoke behaviour. The critical velocity to prevent upstream smoke propagation in the event of a tunnel fire is an important parameter in the design process of a ventilation system. The current techniques for prediction of the values of the critical velocity are mainly based on semi-empirical equations. These equations are obtained from the Froude number preservation combined with available experimental data. Full-scale experimental test programs are expensive which stimulates the application of numerical simulation to these design problems. Simulated full-scale point supply ventilation system of Memorial Tunnel in USA is investigated. Three-dimensional simulation of smoke flow in the tunnel is carried out using FLUENT 6.3.The model includes component models for turbulence, fire, radiation heat transfer, and smoke production. The impact of fire size on critical velocity is investigated. The findings from the numerical simulations supported the published results of experimental test program and also the three semi-empirical correlations found in literature. This suggests that the simulation techniques can be used with confidence to predict the critical ventilation velocity for large-scale tunnels. Moreover, it recommends the point supply ventilation system as a competitive alternative for conventional longitudinal ventilation system.

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