Drag Coefficient and Correlation Equation for Ahmed-Model-Based Vehicle Platoon Driving in Terms of Speed and Distance Ratio

The Ahmed model significantly simplifies general vehicle geometry and has been employed extensively as a reference model for drag mechanism analysis. Platooning is a driving strategy that can reduce aerodynamic drag through intervehicle aerodynamic interactions. In this study, numerical analyses were performed under two-, three-, and four-vehicle platoon-driving conditions of the Ahmed model at various speeds and intervehicle distances. A RANS-based shear stress transport k–ω turbulence model was used to predict the drag coefficient (Cd) changes. A comparison with previously studied experimental data demonstrated high reliability, with a relative error of 0.6–5.0%. CFD analysis results showed that the drag reduction was significantly greater at shorter intervehicle distances, and that increasing the number of vehicles in a platoon reduced the fuel consumption. Furthermore, the intervehicle fluid interactions weakened and the Cd values became more similar with an increasing intervehicle distance. On this basis, a Cd correlation was proposed in terms of the speed and intervehicle distance. Our quantitative evaluation of the aerodynamic interactions between multiple vehicles during platoon driving and the analysis of Cd correlations that are applicable to real-world conditions can improve fuel efficiency and reduce carbon emissions in real-world transportation systems.