windpuls simonaero: validation of unsteady aerodynamic effects for single vehicles and vehicle platoons under real-world apparent flow conditions.

Validation of CFD methods against real-world measurements is particularly challenging under unsteady and disturbed flow conditions. In on-road and proving ground scenarios, vehicles are exposed to time-varying apparent wind fields resulting from environmental influences and vehicle interactions. This effect is amplified in vehicle platoons, where the aerodynamic coupling between multiple vehicles leads to complex, unsteady flow regimes. This paper presents an integrated test and validation toolchain designed to correlate steady-state CFD simulations with real-world measurements for single vehicles and vehicle platoons under unsteady apparent flow conditions. The presented use case focuses on proving ground measurements capturing time-resolved apparent flow conditions acting on both vehicles within a platoon. The apparent wind profiles include wind magnitude, incident flow angle, gust index (GI), turbulence intensity (TI), and side wind exposure (SE), derived from synchronized high-frequency (100 Hz) vehicle and environmental measurements. The toolchain enables structured acquisition, synchronization, and evaluation of the experimental data, including quality assessment and scenario-based segmentation, while providing simulation correlation and analysis capabilities that allow consistent comparison between measured and simulated aerodynamic responses under quasi-steady assumptions. To enable systematic assessment, measured aerodynamic sensitivities are evaluated across varying real-world side wind profiles and compared with steady-state CFD predictions at corresponding instantaneous flow angles. This approach supports comparison across different platoon configurations (longitudinal distances from 0.3s to 2.5s time gaps, lateral offsets up to ±0.8m, and incident flow angles up to 15°) and driving conditions (40–130 km/h). The correlation results reveal the influence of unsteady apparent flow characteristics on aerodynamic loads and energy-relevant metrics, while also identifying where steady-state simulation assumptions remain valid and where time-varying effects dominate. The presented methodology provides a structured framework for CFD validation under realistic driving conditions, supporting aerodynamic development, platooning strategies, and energy-efficient vehicle concepts.