The aerodynamics of long lorry platoon in a tunnel

Zhang, Xiaotian (2022). The aerodynamics of long lorry platoon in a tunnel. University of Birmingham. Ph.D.

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Abstract

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 research aims to improve our understanding of the aerodynamic phenomena associated with a long vehicle platoon running through a tunnel. The effect of the tunnel existence, blockage ratio, symmetry of the traffic lane and the inter-vehicle spacing on the aerodynamics performance of the long platoon will be investigated.

To achieve this goal, both model-scale experiments and numerical simulations (IDDES) were conducted, and the results are compared to a similar study conducted in the open air.

The slipstream velocity and pressure, the lorry surface pressure, as well as the drag coefficient, were investigated systematically. The results show greater pressure variations when the platoon is running through the tunnel than in open air. 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.

When the blockage ratio decreases, the piston effect becomes less effective, making the flow field and the variation drag reduction ratio approach the pattern observed in the open air. Unlike a single lorry, increasing the blockage ratio does not lead to an increase of the drag of every lorry in the platoon. In a small tunnel, the some intermediate lorries have smaller drag coefficients, while others have larger drag coefficients compared to the lorries in large tunnels. Therefore, the overall drag coefficients of the platoons are not affected by the blockage ratio, except for the platoon with 0.1L spacing.
It is further found that the travelling on the asymmetrical traffic lane may results in some asymmetry of the flow field, but has little influence on the drag and side forces experienced by the lorries.

In the open air, the drag coefficients of all lorries are monotonically decreasing with the spacing due to the stronger shielding effect.
When the spacing reduces to 0.25L, the intermediate lorries have larger drag coefficients than the same lorries in the platoon with larger spacings due to the change of the wake structure and the confinement of tunnel walls. Therefore, the overall drag reduction ratio does not monotonically increase with the decreasing spacing. The inter-vehicle spacing control strategy should be reconsidered when a long platoon travelling from the open air into a road tunnel.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):