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The potential energy-saving benefit for vehicles when travelling in a ‘platoon’ formation results from the reduction in total aerodynamic drag which may result from the interaction of bluff bodies in close-proximity. Early investigations of platooning, prompted by problems of congestion, had shown the potential for drag reduction but was not pursued. More recently, technologies developed for connected-autonomous vehicle control have provided a renewed interest in platooning particularly within the commercial vehicle industry. To date, most aerodynamics-based considerations of platooning have been conducted to assess the sensitivity of drag-saving to vehicle spacing and were based on formations of identically shaped constituents. In this study, the interest was the sensitivity of drag-saving to the shape of the individual platoon constituents. A new reference car, the Resnick model, was specially designed to include front and rear-end add-on sections to make distinct changes in profile form and simulate large-scale body morphing. The results of wind tunnel tests on small-scale models suggested that current trends in low-drag styling may not provide the ideal shape for platoon constituent members and that optimised forms are likely to be dependent upon position in the platoon.

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<div class="section abstract"><div class="htmlview paragraph">The work described in this paper is a continuation of an investigation into the effects of systematic changes in upper-body geometry on the aerodynamic drag of passenger-car-like bluff-body models in close longitudinal proximity and operating in platoon formations. The original work, presented in SAE paper 2019-01-0659, showed measurements of the aerodynamic drag of individual models within three-model platoons and for which each model was tested in three different upper-body configurations This provided a data-set of 27 platoon configurations to compare with the three baseline conditions of the isolated models. The work contrasted with other published platooning research in which the spacing, between homogeneous models in the platoons, was the only variable to be considered.</div><div class="htmlview paragraph">In this publication the results of further wind tunnel tests, using the same models as before but in two-model platoons, providing a further 9 test configurations are compared with the original data. In addition, the results of CFD analyses for both the two and three-model platoon configurations are reported to help provide a more detailed and illustrated explanation of the modification of flow regimes and subsequent forces due to close-proximity.</div><div class="htmlview paragraph">The most significant influence on drag of the proximity tests was shown to be the interference on upstream wakes due to the presence of a following model. The shielding effect provided to trailing models also resulted in a drag reduction by reducing pressure drag on upright nose surfaces. But shielding also resulted in a drag penalty by reducing flow velocity over the radiused leading edges, particularly of the A-pillars thereby reducing a low pressure zone which, in unobstructed flow, yields a drag reduction for the Windsor model.</div></div>