On the determination of the aerodynamic coefficients of highway tunnels

The determination of the aerodynamic coefficients of highway tunnels is crucial to set up an accurate theoretical model of tunnel ventilation. Their appropriate values vary with situations, such as traffic conditions, auxiliary facilities in tunnel, jet fan performance, and so on, and accordingly shall be determined in real situations. More importantly, their inherent situation-dependent characteristics shall be reflected in the model by using relevant aerodynamics and traffic data obtained by in situ measurement, instead of just employing the data obtained from reduced-scale experiments done in laboratory or the data obtained from handbooks. In this paper, we propose an optimization approach that can simultaneously determine the four major aerodynamic coefficients of road tunnels: the friction coefficient of tunnel wall, the averaged drag coefficients of small-sized and large-size vehicles, and the pressure-rise coefficient of jet fans. The approach is based on the data of the dynamic traffic as well as of the traffic-induced wind speed measured in the 1.8-km-long highway tunnel—Fu-De Tunnel located in the suburb of Taipei City. Since the measurement is made in a full-scale tunnel operating under various realistic traffic situations and Fu-De Tunnel is typical in the modern design, we believe that the coefficient values determined in this paper can be used directly in other modern highway tunnels and shall be more appropriate than those determined by other traditional ways.