Aerodynamics allow trucks to "fly"

Flow control techniques and aerodynamic improvements developed at the Georgia Institute of Technology, Atlanta, could save the trucking industry hundreds of millions of gallons of fuel per year. Recent tests using a full-size tractor-trailer demonstrate how the techniques--which are based on systems originally developed for jet aircraft wings--could increase fuel economy by as much as 12%. The modifications also could enhance braking and directional control, potentially improving safety for the big rigs.

"Aerodynamically, we have resolved unknowns raised in earlier testing, and the next step is to get this into a fleet of trucks for more extensive testing," says Robert Englar, principal research engineer in the Aerospace, Transportation and Advanced Systems Laboratory of the Georgia Tech Research Institute. "We have shown that this technology now works quite successfully, and we expect that the industry will find a potential 12% fuel economy improvement worth pursuing. At highway speeds, each one percent improvement in fuel economy results in savings of about 200 million gallons of fuel for the U.S. heavy truck fleet."

The aerodynamic improvements produced by geometry changes--which generate fuel savings of as much as six to seven percent--involve rounding aft trailer corners, installing fairings, and making other alterations that smooth air flow over the boxy trailers. Additional savings of five percent come from pneumatic devices that blow air from slots at the rear of the trailer to further improve and prevent separation of air flow.

Before the pneumatic control system can be used widely, however, researchers will have to choose the best source of compressed air for the blowing system, Englar notes. Options include a diesel-powered motor installed in the trailer like current refrigeration units, bleeding pressurized air from the truck's supercharger, or a simple chain drive to turn air blowers from the trailers wheels. Aerodynamic drag becomes dominant only at higher speeds, so the blowing would be turned off when the trucks were idling or operating at low speeds.

To fully assess the energy savings, the researchers will have to account accurately for the power needed by the blowing system, which will cut into fuel savings. Other practical issues--such as protecting the pneumatic surfaces from damage during docking--still must be resolved, though that effort already is underway.

Beyond boosting fuel efficiency, the pneumatic system can provide a form of aerodynamic braking to assist the mechanical brakes. "Using the pneumatic systems, you can turn a low-drag configuration very rapidly, giving you a lot more braking power," Englar explains.

Differential blowing also could improve control of trailers in crosswinds by helping compensate for the wind direction. 'qhis would allow you to have the blow equivalent of an airplane rudder on the trailer, without any physical additions. Beyond increasing fuel efficiency, the pneumatic system could be a drag reducer, drag increaser, safety factor, and a stabilizing device."

Both the improved braking and directional control could be part of an automated system that would not require special attention from drivers.

Further energy savings could come from employing a pulsed pneumatic system, which preliminary wind-tunnel studies on wings have shown could produce the same aerodynamic efficiency with less energy consumed by the blowing system. Englar hopes to learn how this might affect the truck aerodynamics--as well as fuel consumption.

"Our suspicion is that, by using pulsed blowing, you could reduce the blowing system's fuel requirements by about half to three-quarters," he concludes. "This would reduce the penalty for running this kind of a blown system."

COPYRIGHT 2005 Society for the Advancement of Education
COPYRIGHT 2005 Gale Group