An Investigation of Aerodynamic Characteristics of Three Bluff Bodies in Close Longitudinal Proximity - Part 3: Influence on Lift

The aerodynamic effects of bodies in close proximity continues to be an interest for those involved in aeronautical, automotive and civil engineering together with those involved in sports such as cycling, motor racing and sailing. For passenger cars, research in the USA published in the 1980s had considered travelling in close proximity, termed “platooning”, as a means for reducing congestion. But the aerodynamic drag reduction and fuel-savings found in associated wind tunnel tests and road-trials became the focus of further investigations. Although practical applications were not originally pursued, the recent development of control systems for connected and autonomous vehicles has provided the opportunity for platooning to be considered again within future traffic management systems. Thus while the focus of automotive work to date has been the potential for the reduction in total aerodynamic drag, the associated changes in aerodynamic lift which might influence the characteristics of stability and occupant comfort, have rarely been discussed. This paper contains results from an experimental investigation to show the effect of systematic changes in upper-body geometry on the aerodynamic lift forces of three Windsor models in close proximity. This work was part of an on-going project to consider the influence of styling on vehicles travelling in platoons. It was found that for the range of configurations tested there were significant effects on the axle lift coefficients and model pitching moments due to proximity which would likely cause a degradation in straight-line stability. There does not appear to be a direct correlation with changes in drag for models in the tested configurations.