An Investigation of Aerodynamic Characteristics of Two Bluff Bodies in Close Longitudinal Proximity – Sensitivity to Front-End Geometry

With an increasing focus on the reduction of greenhouse gases by the transport industries and continued development of connected and autonomous vehicle systems, the potential for aerodynamic drag reduction by means of managed systems of vehicles travelling in close-proximity, termed “platooning”, has continued as topic for research. Early-work in passenger-car platooning was conducted by varying the spacing between vehicles in homogeneous platoons. More recently the use of systematic changes in upper-body geometry has provided data for another variable in the assessment of platooning characteristics. The results of the investigation described in this paper adds to previously published platooning results using the Windsor reference model. For this investigation a new add-on geometry to the standard nose was designed to provide a simplified bonnet feature. This was chosen in order to vary the on-set flow approaching the platoon and also to influence the flow in the gap between test models. As previously found, the close-proximity presence of a following model resulted in significant drag reductions for the lead model due to wake suppression. Based on drag accumulation analyses in CFD, the “shielding” effect provided by the lead model gave a more significant drag reduction on the front of the following model when fitted with the bonnet addition compared to the standard nose. But the beneficial acceleration of the flow around the A-pillars of the following model was negated resulting in small total drag increases. As in previous investigations, one significant observation was that none of the upper-body geometries was found to be optimal in every position and combination of models.