All ETDs from UAB

Advisory Committee Chair

Alan M Shih

Advisory Committee Members

Jong-Eun Kim

Roy Koomullil

Document Type


Date of Award


Degree Name by School

Master of Science in Mechanical Engineering (MSME) School of Engineering


Computational fluid dynamic (CFD) simulations of the steady state Reynolds-Averaged Navier-Stokes (RANS) equations using the second order k — ω turbulence model were performed to investigate the Drag Coefficients (Cd) of the Class 8 trucks under different geometric configurations. The reduction rates of aerodynamic drag using several add-on devices such as base flap, boat tail, underbody skirt, and tractor-trailer gap are investigated through the CFD simulations. Moreover, simulations by using different lengths and angles of the base flap and boat tail were conducted; the comparison indicates that the base flap design is more effective for the drag reduction. The optimized range of the length and angle of the base flap design is confirmed by a set of systematic CFD simulations and used as reference for future study to define the optimization design of this add-on device. The objectives of this study are twofold. The first is to conduct the numerical experiments by using the baseline truck geometry to investigate the air flow characteristics, influences of mesh and flow mathematical models, and to find better configurations to reduce the Cd. The results from using the baseline will be used as a benchmark for later comparison with the simulations by attaching different types of the add-on devices. The second objective is to search for a set of optimal geometrical parameters of the base flaps to maximize the drag reduction. In order to validate the effectiveness of the CFD simulations, the wind tunnel experiments with a 1:20 model of the truck were conducted at the University of Science and Technology of China (USTC) by a team of collaborators. The wind tunnel experiments produced similar results as the CFD simulations, which could be considered as a validation to the results from our CFD simulations.

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