Overdrive Magazine | Trucking Business News & Owner Operator Info
Issue link: https://read.dmtmag.com/i/255292
February 2014 | Overdrive | 47 Filling the gap While some aero problems have simple fixes, one big obstacle remains. By JACK ROBERTS A ny vehicle moving at highway speeds faces the impediments of drag, which is created in two ways. One is when anything impedes the smooth flow of air around the vehicle – for example, rearview mir- rors and bug screens. Drag also is created by a vacuum – a low-pressure area that sucks in air that ideally would flow smoothly past the vehicle. The result is turbulence. While bumper-mounted air dams, wheel coverings and trailer side skirts and tails have improved airflow underneath and around tractor-trailers dramatically, the trailer gap re- mains a stubborn aerodynamic challenge for engineers. Computation fluid dynamics and testing have shown that gap drag reacts on the rear of the tractor and its fairing and the front of the trailer, says Mike Henderson, chief scientist for SmartTruck, which makes the UT6-Plus aerodynamic package for trailers. The solution, he says, is to close the gap or place fairings on the front of the trailer's top and sides. Andrew Smith, chief executive officer of ATDynamics, favors a tractor-related solution. "Because of the variation between trucks and trailers, the winning technology to ad- dress this area of drag will be as universal as possible and will be tractor-mounted, given the high ratio of trailers to trucks in most fleets," he says. ATDynamics' Trailer Tail addresses a trailer-related vacuum by using fairings on the rear of the trailer to reduce turbulence. Small vortex generator blades – wishbone-shaped airfoils that smooth airflow over a truck's trailing edges, like the back of a cab or trailer – also can help, says VorBlade's Natalie Melomed. "It might be counterintuitive, but small-scale vortex generators destroy harmful turbulence by intensifying the mix between different pressure zones and compensating the pressure jump," Melomed says. "VorBlades actually reduce drag in the gap and increase vehicle stability." FlowBelow aero devices focus on the fringe of the trac- tor-trailer gap, including wheels and tires. The company's AeroKit package includes fairings between the drive axles and next to the mudflaps. "Because there are many trailer and tractor configura- tions, having to design and build many variations of any solution makes it difficult for a manufacturer to reach econ- omies of scale and offer their product at an attractive price," says Mario Bravo, FlowBelow marketing director. FlowBelow's Tractor AeroKit system of aerodynamic devices includes wheel covers and is designed to work with many different wheel and tire configurations, including super singles. VorBlade's small vortex generator blades are wishbone-shaped airfoils that smooth airflow over a truck's trailing edges. Filling_the_Gap_0214.indd 47 1/28/14 11:19 PM