A Qualitative Experimental Study of Drag Reduction Devices for Tractor Trailers with Ground Effects

This is an experimental qualitative study of how drag reduction devices affect air flow around a tractor trailer. A 1/32 scale detail model of a truck with its trailer was used for testing in a 20"x14" low speed wind tunnel at the University of Tennessee Space Institute. Major modifications were made to the wind tunnel so that it would include a moving bed (floor) section for ground effect simulation. This was done to accurately simulate relative ground movement with the truck being held stationary in the tunnel flow.

Drag reduction devices were designed based on aerodynamic fundamental understanding for streamlining the various zones of the truck readily available for flow path modifications or flow management around the truck. The drag reduction devices were fabricated using a desktop 3D printer. Flow visualization was performed using sewing (twisted) string as tufts to validate if there were any flow improvement effectiveness as a result the flow management devices. A total of 102 tests were performed. This was done using 24 unique drag reduction devices, which were tested in 28 different configurations. Wind tunnel speed was in the range of 55 to 70 PMH at a corresponding tunnel unit Reynolds number of 5.6*10^5 to 7.12*10^5. Observations show that each device affects the flow, locally, and that an overall change in aerodynamic efficiency (drag reduction) can be achieved by the addition of a number of these devices.

Test results from this investigation showed that the addition of drag reduction devices did change flow paths under the tractor trailer and did provide methods for managing flow under the trailer. A possible novel method for addressing the wake zone behind the tractor trailer, by addition of drag reduction devices installed under the trailer, was also investigated.

Quantitative measurements are needed to determine the overall and individual contributions, and to select the best configuration of a number of configurations for maximum level of drag reduction.