Journal Article

Unsteady Drag Analysis of Platoon Vehicles Using Unsteady Reynolds-Averaged Navier-Stokes and Improved Delayed Detached Eddy Simulation

Yudianto, Aan

2025

Overview

The aerodynamic interaction of vehicles in platoon formation generates complex unsteady flow phenomena that strongly influence drag performance. This study investigates the unsteady aerodynamic drag and associated flow structures of two simplified Ahmed body models (30° slant angle) traveling in platoon using transient Computational Fluid Dynamics (CFD). Unsteady Reynolds-Averaged Navier–Stokes (URANS) and Improved Delayed Detached Eddy Simulation (IDDES) are employed to analyze the effect of longitudinal spacing ratios, d/L=0.1–2.0. Following a mesh independence study, a grid with 13.3 million cells is adopted to resolve the flow field and quantify drag unsteadiness for both the lead and trailing vehicles across spacing configurations. Validation is performed by comparing the predicted drag coefficients with experimental measurements. Results show that the lead vehicle experiences a substantial drag reduction, with the coefficient decreasing to 0.16 at close spacing, before rising to 0.40 (URANS) and 0.37 (IDDES) at d/L=2. In contrast, the trailing vehicle exhibits only minor drag variation across d/L=0.5–2, ranging between 0.35 and 0.37. Additional analyses include pressure coefficient distributions, instantaneous velocity fields, and vortex structures identified through Q-criterion visualizations. Comparisons indicate that IDDES captures finer flow structures and better reflects   the unsteadiness of drag than URANS. Overall, the results suggest that the lead vehicle benefits most from platooning, achieving up to 60% drag reduction at small spacings, whereas the trailing vehicle gains comparatively little.