Evaluation of vehicle platooning aerodynamics using bluff body wake generators and CFD

Recent developments in sensing and communications between vehicles (V2V) and their surroundings have provided the technology to allow cars to operate autonomously or semi-autonomously in closely spaced `platoon' formation without the risk of collision. This is known to reduce the aerodynamic drag and thus consequently limits the energy consumption and associated emissions. Although wind tunnel investigations have been performed to mimic platoon operations, most experimental evaluations of multiple vehicles in platoon are severely compromised by the restricted length of the wind tunnel test section. Therefore, the model scale must be reduced which decreases the measurement accuracy. The innovative solution presented here is to reproduce the flow structure that is created by a leading road car through the use of a `bluff-body wake generator' with a much reduced length which eliminates the need to decrease the scale of the following test model. Validated computational fluid dynamics (CFD) data and analysis are presented to evaluate an optimized design of a wake generator based on the Ahmed model [1] and the effect of inter-vehicle spacing on the aerodynamic characteristics of the following vehicle. It is shown that accurate reproduction of the wake is possible at half the characteristic length, thus correctly determining the flow impact on the downstream model. This demonstrates that the bluff body wake generator provides a reliable approach that allows platooning studies to be performed without sacrificing aerodynamic resolution.