Design Optimization of Tractor-Trailer Drag Reduction

Drag reduction is one way to reduce vehicle fuel consumption. Tractor-trailers have a higher drag coefficient than other vehicles due to their bluff-body shape. Over the years, numerous add-on devices have been invented to help reduce drag and fuel consumption. The current research extends our previous idea of add-on humps and investigates their effect in conjuction with curved boat-tail flaps. Computational fluid dynamics (CFD) in the form of unsteady Reynolds-averaged Navier-Stokes (URANS) and detached-eddy (DES) simulations were used to determine viable design strategies. Design optimization was applied on the new add-on devices. A 3D baseline computational model was constructed using an Ahmed body. The predicted drag coefficient of the baseline configuration showed good agreement with experimental data. The results from the optimized design with add-on humps and curved boat-tail flaps are shown to have a 50.9 % reduction in drag coefficient. The predicted results using three different turbulent models, including standard k-ε, RNG k-ε, and DES, were compared with each other. Predictions with the standard k-ε model produced the best agreement with the baseline experimental drag coefficient. Nomenclature Cd = drag coefficient CP = pressure coefficient h = maximum hump height l = Ahmed body length (excluding head) L = curved flap length X = location of the maximum hump height in the x-direction Ө = angle of rotation φ = slant angle I