An Investigation of Aerodynamic Characteristics of Three Bluff Bodies in Close Longitudinal Proximity

The potential benefit for passenger cars when travelling in a ‘platoon’ formation results from the total aerodynamic drag reduction which may result from the interaction of bluff bodies in close-proximity. In the 1980s this was considered as an opportunity to alleviate congestion and also for fuel-saving in response to the oil crises of the 1970s. Early interest was limited by the availability of suitable systems to control vehicle spacing. However, recent developments in communication and control technologies intended for connected and autonomous driving applications has provided the potential for ‘platooning’ to be incorporated within future traffic management systems. The study described in this paper uses a systematic approach to changes in vehicle shape in order to identify the sensitivity of the benefits of platooning to vehicle style. The Windsor bluff-body model with its’ interchangeable rear-end geometry was chosen as the test subject because of its similarity to the approximate proportions of typical mid-sized European passenger cars. Three small-scale models were manufactured so as to be accommodated in-line within the working section of the Coventry University wind tunnel. Aerodynamic drag results were determined for 27 combinations of 0°, 10° and 25°backlights at zero yaw. The results showed that the aerodynamic efficiency of the platoons was highly dependent upon the shape and position of different body styles. Total drag reductions for the platoons ranged from 12% to 21% depending on backlight configuration. Not all vehicles in the platoons realised an individual drag saving.