Results of a 3-year program to investigate aerodynamic means to reduce fuel consumption of tractor-trailer trucks are reported. The study considers the benefit of aerodynamic add-on devices to reduce the aerodynamic drag on existing vehicles, and the influence of design alternatives in reducing the drag of future vehicles. Results are obtained for scaled-models in water table and wind-tunnel experiments, and for full-scale vehicles in coast-down and fuel economy tests. Wind statistics, analyzed to estimate national-average highway wind conditions, and basic aerodynamic data obtained in the experiments are used to define a wind-averaged aerodynamic drag, or drag reduction for national-average operating conditions. Drag reductions of both commercial and newly-developed retrofit drag reducing devices are evaluated. Full scale test results indicate that wind turbulence effects cause the full-scale drag reductions produced by retrofit devices to be generally less than those found in the wind tunnel. The decrease is found to be a function of the design of the device and the ambient conditions in which it is used, and is the least for a fairing/gap seal combination which produces wind-averaged aerodynamic drag reductions of up to 36% in wind-tunnel experiments.
Abstract