Numerical analysis for reduced-scale road tunnel model equipped with axial jet fan ventilation system

In this paper a preliminary tridimensional CFD analysis is carried out for a future realization of a reduced-scale road tunnel experimental apparatus of 1/50 equipped with different impulsive fans, traditional and alternative. The alternative jet fan is provided of inlet/outlet sections inclined at a fixed pitch angle (a=6°) toward the tunnel floor. Typically, in the experimental scale tunnel model the air flow induced by ventilation system is provided by an external fan and fully developed flow field is considered. In this paper, the authors have simulated a realistic full and reduced-scale tunnel in order to evaluate the influence of ceiling and floor roughness height on the velocity field to identify an appropriate material for a future experimental apparatus. The jet fans are simulated as a simple momentum source. The fan is considered to be infinitely thin and the discontinuous pressure rise (pressure drop) across it is defined as a function of the air velocity through the fan. In order to create a reduced-scale model from a full scale, Froude method is applied to preserve geometrical, kinematical and dynamical similitude. The results, provided in terms of axial velocity profiles in different tunnel sections, show the overlapping between velocity profiles of full scale numerical model with those of the reduced-scale model, for the both ventilation systems.