An Evaluation of the Aerodynamic Drag Reductions Produced by Various Cab Roof Fairings and a Gap Seal on Tractor-Trailer Trucks

A study has been carried out to determine the reduction in the aerodynamic drag of tractor-trailer trucks brought about by fairings mounted on the cab roof and a vertical seal mounted across the gap between the tractor and the trailer. This study was conducted using one-eighth-scale models in a wind tunnel at a Reynolds number of about 25 percent of that of full scale trucks at 50 mph. Reductions of up to 35 percent of the zero-yaw drag coefficient, and of over 25 percent of the wind-averaged drag coefficient were obtained. The drag reductions obtained with roof fairings, with and without gap seals, significantly exceeded those obtained with a commercially-available roof deflector, with and without a vortex stabilizing device.

Comparison with other model tests and a full-scale test indicates that the results obtained in this study should be directly applicable to full-scale trucks.