Optimal pitch angle of jet fans based on air age evaluation for highway tunnel ventilation

Abstract

The Coandă effect on jet flow can be solved effectively using the jet fan with a pitch angle in highway tunnels. In this study, the ventilation efficiency of the jet fan with a pitch angle in the range 0–12° is tested using the computational fluid dynamics (CFD) method with experimental validation. The mean air age in volume (MAA-V) is applied to evaluate the ventilation effectiveness in the full space and clearance space of tunnel. The results show that the jet fan with a pitch angle can significantly alleviate vortices caused by the jet flow. The pitch angle of 7° can provide a desirable compromise for MAA-V, found to be 13.62% and 20.67% younger than that of 0° for the full and clearance spaces, respectively. Furthermore, the pressure-rise coefficient at different pitch angles is also investigated, and the maximum is obtained at the pitch angle of 7° as well. Finally, the pitch angle of 7° is determined as the optimal angle for the jet fan, which is of great benefit for improving ventilation effectiveness and saving installed power in highway tunnels.