Optimizing the Performance of Vertically-Mounted Jet Fans in Ventilation Shafts

By offering savings in space and capital cost compared to fully ducted axial and centrifugal fan systems, horizontally-mounted jet fans are commonly used worldwide to ventilate vehicular tunnels. They discharge high-velocity jets to transfer momentum to the surrounding airstream to induce longitudinal flow in the same direction as the jet. Vertically-mounted jet fans installed in exhaust ventilation shafts have also been successfully used to ventilate a large passenger rail overbuild in New York City. A total of 28 jet fans are installed in 11 shafts constructed above two passenger rail line tracks. Jet fans require a length of downstream shaft in which to transfer momentum to the surrounding air. A comparison of overbuild shaft dimensions, vertical placement of the jet fans, and measured shaft airflows is presented. Measured shaft airflows are compared to airflows predicted by computational fluid dynamics (CFD) simulations of a three-dimensional model of the overbuild.