A wind-tunnel study was carried out to determine the influence of some tractor and trailer geometries on the distribution of aerodynamic drag of tractor-trailer trucks. Also investigated were the effects on the drag distribution of drag-reducing devices and of exhaust stacks. The measurements were made on 1/8th-scale models at a Reynolds number of 106.
The shape of the tractor strongly influenced the drag on the trailer. Streamlining the tractor could increase the drag on the trailer to the point that the drag on the tractor-trailer combination increased.
A relatively streamlined conventional tractor was responsible for between 45% and 57% of the total aerodynamic drag at 0° yaw, whereas a relatively unstreamlined cab-over-engine tractor was responsible for between 73% and 82% of the zero-yaw drag.
A streamlined fairing mounted on the tractor increased the drag on the tractor, but decreased the drag on the trailer substantially more than the drag on the tractor increased.
Exhaust stacks were found to significantly reduce the drag on a tractor-trailer combination.