The efficiency of longitudinal ventilation in road traffic tunnels

The efficiency of a jet fan placed at different locations in a tunnel cross-section was investigated in a 1:10 scaled test facility for road-traffic tunnel ventilation tests. Measurements were performed at various tunnel velocities with the jet fan in operation at various RPM and with and without guide vanes in the fan exit. Pressure and velocity profiles and the fan thrust force were measured in order to determine fan installation efficiencies. Test results were compared with the previous tests of the central positioned fan without guide vanes. Weather conditions outside the tunnel might have some influence on the flow and pressures at the entrance of the tunnel. The efficiency of another approach of ventilation, using a group of fans installed at the tunnel entrance (so-called "injectors"), was also investigated. In these tests three or five injectors were installed at the tunnel entrance and different tunnel entry shapes were used. In this case the collective thrust of the injectors was such that at low tunnel velocities significant local backflow regions occurred in the tunnel. With the injectors in operation the influence of stationary traffic (simulated by schematic scaled lorries) in the entrance region was also investigated.