Investigation of Tractor Base Bleeding for Heavy Vehicle Aerodynamic Drag Reduction

Abstract

One of the main contributors to the aerodynamic drag of a heavy vehicle is tractor-trailer gap drag, which arises when the vehicle operates within a crosswind. Under this operating condition, freestream flow is entrained into the tractor-trailer gap, imparting a momentum exchange to the vehicle and subsequently increasing the aerodynamic drag. While a number of add-on devices, including side extenders, splitter plates, vortex stabilizers, and gap sealers, have been previously tested to alleviate this source of drag, side extenders remain the primary add-on device of choice for reducing tractor-trailer gap drag. However, side extenders are not without maintenance and operational issues. When a heavy vehicle pivots sharply with respect to the trailer, as can occur during loading or unloading operations, the side extenders can become crushed against the trailer. Consequently, fleet operators are forced to incur additional costs to cover the repair or replacement of the damaged side extenders. This issue can be overcome by either shortening the side extenders or by devising an alternative drag reduction concept that can perform just as effectively as side extenders. To explore such a concept, we investigate tractor base bleeding as a means of reducing gap drag. Wind tunnel measurements are made on a 1:20 scale heavy vehicle model at a vehicle width-based Reynolds number of 420,000. The tractor bleeding flow, which is delivered through a porous material embedded within the tractor base, is introduced into the tractor-trailer gap at bleeding coefficients ranging from 0.0-0.018. To determine the performance of tractor base bleeding under more realistic operating conditions, computational fluid dy-

Aerodynamic drag reduction of class 8 heavy vehicles: a full-scale wind tunnel study

“…From these studies, the average fuel savings of the gap, skirt, and boattail devices are about 3000, 5000, and 4000 L/2.012×10 8 m driven of highway mileage, respectively, while that of their combinations is on average approximately 12000 L/2.012×10 8 m driven of highway mileage. Other research concepts that have been recently investigated include tractor and trailer base blowing systems [18,19,43], fluidic actuators [26,41,51,52,63] and trailer wheel and bogie fairings [15,42,55].…”