Investigation of the aerodynamic phenomena associated with a long lorry platoon running through a tunnel

In recent years, the concept of vehicle platooning has gained widespread attention for its highly efficient road usage and lower fuel consumption. However, the aerodynamics of vehicle platoons travelling in a tunnel are not well understood, even though more and more road tunnels have been built to alleviate the traffic congestion problem. This paper presents a detailed study of the aerodynamic flow created by a long lorry platoon running through a tunnel, conducted via a combination of model-scale experiments and Improved Delayed Detached Eddy Simulations (IDDES). The slipstream velocity and pressure, the lorry surface pressure, as well as the drag coefficient, were investigated systematically and compared with the results obtained in the open air. The results show greater pressure variations when the platoon is running through the tunnel. The piston effect in the tunnel leads to a lower approaching velocity and a weaker flow separation compared to the case in the open air. All vehicles, in both the tunnel and the open air, experience a drag reduction due to platooning. Interestingly, the drag reduction in the tunnel is 20% greater than that in the open air, implying a greater potential in fuel saving.