Fluid dynamic performances of traditional and alternative jet fans in tunnel longitudinal ventilation systems

This paper presents the results of a numerical investigation carried out on an alternative jet fan, known in literature like Banana Jet, and it compares its fluid dynamic performances to traditional axial ventilation systems. The alternative jet fan is equipped with inlet/outlet sections inclined at a fixed pitch angle (a) toward the tunnel floor. This approach establishes an alternative solution that is able to provide a safety level equivalent to the traditional solution, in different scenarios. Both systems are installed in an oneway tunnel and two different scenarios (without vehicles and with traffic jam) are considered, in event of fire. The fire was simulated setting heat flux on Heavy Good Vehicle (HGV) surface and comprehensive of radiative heat flux. Computational Fluid-Dynamic (CFD) are applied to simulate the ventilation in the unidirectional tunnel through k–e model, including temperature fields. The results show, for both scenarios, the existence of an optimal pitch angle which offers advantages in comparison with the traditional system (a = 0) in terms of plant and running costs. In the next paper, the influence of the radiative heat flux for the optimal pitch angle will be explicitly considered.