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Kambiz Salari and the Aerodynamics of Trucks

Trucks waste a lot of energy overcoming the drag created by their boxy frames. Designing sleeker big rigs, though, is harder than designing sleeker airplanes given that cargo containers can’t be anything other than rectangular. Kambiz Salari puts the challenge this way: “Here is a box, and you have to somehow make it more aerodynamic, but it’s still a box.”

Salari, 53, is a researcher at Lawrence Livermore National Laboratory, and has spent the last decade figuring out ways to make trucks slice through the air more gracefully. His research meshes with a new national imperative: The Energy Dept. awarded $115 million in grants last year to develop “super trucks” that are 50 percent more fuel efficient by 2015. Salari says we can get part of the way there—a 17 percent efficiency gain—by making relatively modest tweaks to a truck’s contours.

An expert in the field known as computational fluid dynamics, Salari uses software to simulate the flow of air across a truck’s exterior. Certain areas, such as the underbody or the gap between the trailer and the cab, cause a lot of resistance, but even the “grab handles” that drivers use to climb into their seats create drag. Salari’s complex models take days to compute, even using Livermore’s supercomputers.

The simulations help Salari’s team zero in on the most promising design modifications, which they then test in the world’s largest wind tunnel, at NASA’s Ames Research Center in Silicon Valley. One product they’ve tested is the “truck skirt,” a pair of flat panels that drop down from the sides of the truck to redirect air away from the underbody. Skirts have been available for years, but many truckers question whether they work. Salari’s research proves they do. Over the next 18 months, he expects to publish more such conclusions to help trucking companies evaluate products on the market and design new ones.

Together, Salari’s suggested changes could improve trucks’ fuel economy to about 6.3 miles per gallon, up from an average of 5.4 today. He says it could save the shipping industry 6 billion gallons of diesel and $24 billion a year. Andrew Smith, founder of ATDynamics, says Salari’s work helped “us to write a business plan.” His company makes a large attachment that fits on the back of a trailer and reduces the vacuum behind a truck.

Salari, who emigrated from Iran as a teenager, says he’s been fascinated by the complexities of air flows since his undergraduate days at the State University of New York at Stonybrook. After earning a mechanical engineering PhD at the University of New Mexico, he studied such air-flow topics as how hypersonic jets fly and how explosions affect fluids. To Salari, making sleeker tractor trailers is just as fascinating. “It takes years to develop a sense of how the flow behaves,” he says.


Uses supercomputers and wind tunnels to study air flows.


Researched hypersonic jets, explosions, and dragonflies.


Design tweaks could increase trucks’ efficiency by 17 percent.

Tozzi is a reporter for Bloomberg Businessweek in New York.

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