Passive drag reduction of square back road vehicles

• Published in: Journal of wind engineering and industrial aerodynamics 2014-11, Vol.134, p.30-43
• Main Authors: Altaf, Alamaan, Omar, Ashraf A., Asrar, Waqar
• Format: Article
• Language: English
• Subjects: Aerodynamics; Bluff bodies; Bluff body; Buses (vehicles); CFD; Drag; Drag reduction; Elliptic flaps; Equivalence; Flaps; Passive drag reduction; Road vehicles; Trucks
• ISSN: 0167-6105; 1872-8197
• DOI: 10.1016/j.jweia.2014.08.006

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°. 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 0.12m semi-major axis; compared to 6.37% 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.