Drag Reduction of Bluff Vehicles With Airvanes

An experimental wind tunnel program has been conducted to evaluate the drag reduction potential of airvanes located in close proximity to the leading and trailing edges of bluff vehicles. The airvanes are modified airfoils that direct an interior portion of the main airflow around a corner. In an optimal design, flow visualization experiments (with tufts) indicate that the outer flow is attached to the exterior vane surface. Front-mounted airvanes reduced the drag of a 1/20 scale, square-cornered trailer (or bus) model by 38% for wind speeds between 40 and 120 mph. With a streamlined cab in position, there was a 30% drag reduction. Rear-mounted airvanes provided an additional 3-6% drag reduction, but were found to be prone to interference effects. The study was limited to the zero crosswind condition and only one airfoil shape was evaluated. Of the parameters tested, airvane efficiencies were most sensitive to changes in the stand-off distances between the vane and the model surfaces. In a full-scale configuration, the airvanes need only protrude 1-2 in from the vehicle sides or roof.