Numerical study of the optimization of the pitch angle of an alternative jet fan in a longitudinal tunnel ventilation system

This paper presents the results of a numerical investigation carried out on an alternative jet fan, noted in literature like Banana Jet Fan, equipped with inlet/outlet silencers inclined at a fixed pitch angle (a) inclined toward the tunnel floor. The aim of this paper is to optimize the pitch angle comparing the different ventilation performances, in terms of reduction of pressure losses and of energy saving, without vehicles and with traffic jam. The average velocity profile variation of the tunnel air jet around the outlet jet fan zone was evaluated with the numerical CFD analysis. This analysis showed that there exists an optimal pitch angle which minimizes the pressure losses, due to the flow attachment by varying the operative conditions (free tunnel and traffic jam).