An improved model of traffic force based on CFD in a curved tunnel

• Effects of vehicle space on tunnel ventilation is investigated with both 1D model and CFD in a curved tunnel.
• A flaw is found in prediction of traffic force with 1D model in traffic jam and shorter vehicle space conditions.
• An improved model of traffic force is proposed based on the CFD results in the curved tunnel ventilation.
• The effective drag coefficient is concluded to be among 0.85–1.16 for a large size vehicle in the curved tunnel.

In this work, a numerical study using 1D (one-dimensional) model and CFD (Computational Fluid Dynamics) is developed to analyse effects of vehicle space on the ventilation and the results from CFD are employed to improve the accuracy of the traffic force model in a highway curved tunnel with a radius of 600 m. The air speed from 1D model is compared to that from CFD for a single vehicle in the tunnel and a good agreement is concluded. The air speed from both 1D model and CFD for two vehicles is shown to increase significantly with the increase of vehicle speed and the number in the tunnel. However, the effective piston effect coefficient exhibits two opposite variations for the two models. The absence of the effect of vehicle space in 1D model is considered to be responsible for its unreasonable result. An understandable result from CFD is observed that the effective piston effect coefficient increases with the increase of vehicle space and the decrease of vehicle speed. It is subsequently used to improve the traffic force model. The effective drag coefficient increases significantly with the increase of vehicle space, especially in a shorter vehicle space. The effective drag coefficient is concluded to be among 0.85–1.16 for a large size vehicle in this study.