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Commercial heavy trucks are characterized as bluffbodies and have unsteady wake flows and high base drag. Base drag has been studied for many years as a primary target for aerodynamic drag reduction. Many aftend devices have been created for active or passive reduction of base drag. Base flaps are one type of device that have shown promise for drag reduction. They consist of 3 or 4 panels joined at their edges to form an open box structure. Although base flaps have been shown to reduce drag, they have not been adopted by the trucking industry because they are inconvenient to deploy on a commercial scale. A practical refinement to base flaps is the two-panel wake board (WB). It is a commercially viable solution, with easy deployment and significant drag reduction. This paper presents experimental data for two-panel wake boards with varying width and inset on an Ahmed body at yaw angles up to 12 degrees.

Aerodynamic drag, lift, and side forces have a profound influence on fuel efficiency, vehicle speed, stability, acceleration and performance. All of these areas benefit from drag reduction and changing the lift force in favor of the operating conditions. The present study simulates the external flow field around a heavy truck with three prototype add-on drag reduction devices using a computational method. The model and the method are selected to be three dimensional and time-dependent. The Reynolds-averaged Navier Stokes equations are solved using a finite volume method. The Renormalization Group (RNG) k-ε model was elected for closure of the turbulent quantities. The run cases were chosen so that the influence of each drag reduction device could be established using a regression model from a Design of Experiments (DOEX) derived test matrix.