Passive drag reduction of square back road vehicles

Bluff body vehicles such as trucks and buses do not have a streamlined shapes and hence have high drag which can be reduced to make great savings in operational cost. While rectangular flaps have been widely studied as both passive add-ons and in active drag reducing systems for bluff bodies, changing the basic geometry of the flap has not been explored in literature. In this work, a baseline drag value is obtained for a simplified MAN TGX series truck in a CFD software, and the drag reduction of a proposed elliptically shaped flap is compared to aerodynamically equivalent rectangular flaps. The optimal mounting angle for both flaps is found to be 50 degrees. A parametric study of changing the ellipse semi-major axis is carried out to find the optimal length for drag reduction. A maximum drag reduction of 11.1% is achieved using an elliptical flap with 0.12 m semi-major axis; compared to 637% for a length equivalent rectangular flap, and 6.84% for a surface area equivalent rectangular flap. Results of the pressure distribution and velocity flow behind the rear of the truck are also given and analyzed. (C) 2014 Elsevier Ltd. All rights reserved.