Reshaping the exterior of heavy vehicles, such as semitrucks, so that they are aerodynamically integrated along their entire length in a smooth, continuous fashion could reduce drag, increase fuel efficiency and cut carbon emissions.
Using wind tunnel measurements and computational fluid dynamics simulations, Lawrence Livermore National Laboratory (LLNL) engineers have demonstrated that aerodynamically integrated vehicle shapes decrease body-axis drag in a crosswind, creating large negative front pressures that effectively “pull” the vehicle forward against the wind, much like a sailboat. The research appears in the Proceedings of the National Academy of Sciences.
Within the United States, domestic freight is dominated by heavy vehicles, which handle approximately 81 percent of the total freight weight and nearly 86 percent of the total value of freight shipments. Although heavy vehicles comprise just 4 percent of all on-road vehicles, they are responsible for more than 20 percent of all transportation-related fuel consumption and greenhouse gas emissions. One of the main sources of inefficiency contributing to the low fuel economy (about 6 miles per gallon) of heavy vehicles is their relatively large body-axis drag.
“Future reductions in petroleum use and carbon emissions will rely heavily upon improved heavy vehicle freight efficiency,” said LLNL computer scientist Kambiz Salari, lead author of the study. “We’ve come up with a solution that would completely transform the trucking industry to become more fuel efficient while helping save the planet by cutting carbon emissions.”
Current drag reduction devices in use today include boat tail plates, trailer skirts and tractor side and roof extenders. Boat-tail plates increase the trailer base pressure, while trailer skirts and tractor side and roof extenders decrease the amount of crosswind flow on the front faces of the trailer and the trailer wheels, respectively.