|The Clarkson boat tail during geometry optimization testing.
Vehicle drag is a costly problem for the long-distance heavy-duty trucks. A modern Class 8 tractor-trailer can weigh up to 80,000 pounds and have a wind-averaged drag coefficient around CD=0.60. As speed increases, so does the energy required to overcome aerodynamic drag. At 70 mph, overcoming aerodynamic drag represents about 65% of the total energy expenditure for a typical heavy truck.
A team at Clarkson University has developed a new implementation of an well-known concept to alleviate some of the drag: an unventilated, planar-sided cavity device attached to the rear of the trailer—also known as a boat tail.
The Clarkson implementation, which is designed to minimize interference with the vehicle and is now being patented, delivers more than a 0.6 mpg improvement in fuel economy in preliminary testing, according to Prof. Ken Visser, the research leader. That might sound like a low figure, but in the context of a vehicle that delivers 5 to 6 miles per gallon, that’s better than 10%.
The Clarkson researchers evaluated more than 100 different design geometries, where cavity length, boat tail angle, and inset from the trailer edge were varied at yaw angles up to 9 degrees. They found that the optimum geometry of a four-foot device with a boat tail angle of 10° and no inset could reduce the indicated drag coefficient up to CD=0.12.
Composite Factory of Plattsburgh, NY has teamed up with Clarkson University to develop a prototype of a viable commercial version of the open cavity design. The researchers are organizing a year-long fleet test of 50 vehicles to confirm the results under varied real-world operating conditions.