Computational study of effects of jet fans on the ventilation of a highway curved tunnel

Abstract

A computational study was carried out to investigate the aerodynamic behavior of jet fans in a curved road tunnel and its effects on the tunnel ventilation system. It has been found that the variations of the static and dynamic pressure in a curved tunnel are non-monotonic. After the issue of the jets, the pressure initially increases gradually, but this is followed by a sudden drop and then a recovery. This is attributed to the interaction between the jets and the curved walls of the tunnel. A sudden increase in pressure is resulted as the jet reaches the convex wall, whereas that the concave wall is approached causes a pressure reduction. The flow becomes asymmetrical downstream of the jets. The development of the jets depends on the separation of the fans and the distance between the fans and the tunnel walls. Increasing the space between the fans or moving them away from the tunnel ceiling makes the jets spreading more quickly across the cross-section. However, it takes a longer distance for the jets to develop when the fans are close to each other or to the tunnel wall. The distance required for pressure to be fully recovered is approximately 90–120 m in this study. The biggest pressure-rising coefficient is obtained when the fans are arranged according to the distance of 2.4 m between the fans, the fans offset of 0.5 m from the centre line towards the convex wall, and the ratio of the distance between fans and the ceiling to the diameter of fans of 1.77.