Large trucks drag reduction using active flow control

Aerodynamic drag is the cause for more than two-thirds of the fuel consumption of large trucks at highway speeds. Due to functionality considerations, the aerodynamic efficiency of the aft regions of large trucks was traditionally sacrificed. This leads to massively separated flow at the lee side of truck trailers, with an associated drag penalty: roughly a third of the total aerodynamic drag. Active Flow Control (AFC), the capability to alter the flow behavior using small, unsteady, localized energy injection, can very effectively delay boundary layer separation. By attaching a compact and relatively inexpensive "add-on" AFC device to the back side of truck trailers (or by modifying it when possible) the flow separating from the truck trailer could be redirected to turn into the lee side of the truck, increasing the back pressure, thus significantly reducing drag. A comprehensive and aggressive research plan that combines actuator development, computational fluid dynamics and bench-top as well as wind tunnel testing was performed. The research uses an array of 15 newly developed suction and oscillatory blowing actuators housed inside a circular cylinder attached to the aft edges of a generic 2D truck model. Preliminary results indicate that a net drag reduction of 10% on full-scale trucks is achievable.