Study on jet fan performances under longitudinal airflow directions in road tunnels

Abstract

To achieve the objectives described in the title, CFD simulations were implemented given two high-velocity jet fans located in parallel in a horseshoe cross section tunnel with two traffic lanes. The simulations without wall friction showed that Meidinger's equation is right only when the longitudinal airflow has the same direction with the jet fan's output flow (LSD), but that under the opposite longitudinal airflow (LOD) the equation by Ishida (JSME, 1991) is right. The simulations with wall friction also showed that the boosting pressure decreases in LSD, but increases in LOD. These phenomena occurs due to local airflows around the jet fans. We also guess different situations may happen dependent on LSD or LOD.