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The Aerodynamics of Trucks: Getting in the Flow

Nina Welding • DATE: November 21, 2016

Categories:  Press Release

NASCAR, IndyCar, and Formula 1 drivers understand the importance of high-performance aerodynamics to their vehicles. It can mean they finish a lap a half second faster than the other cars on the track and use less fuel while doing so. In very tight contests, it can mean the difference between winning the race or even finishing. But these drivers are not the only professionals who appreciate how reducing drag affects a payday. The nearly 3.5 million truck drivers who crisscross America delivering food, fuel, and other products know as well as anyone how airflow not only affects their trips but also the bottom line for every product across each industry they serve. Trucks, and their aerodynamics, are critical to our nation and our economy.

Think about it. Time, distance, mode of transport, these are some of the factors that affect the price of a product. According to the American Trucking Association, 69% of all goods carried by every mode of domestic freight transportation — just under 10 billion tons of freight — is moved by the trucking industry each year, largely Class 8 trucks (vehicles with three or more axles).

What does it take to move close to 10 billion tons of freight? Approximately 3.5 million vehicles and drivers and more than 37 billion gallons of fuel. With the national price of diesel fuel averaging $2.44 per gallon, those costs add up quickly. Now factor new greenhouse gas and emission standards and other operating costs against the bottom line? No wonder that grocery bill keeps ticking up.

The challenge to the transportation industry is clear: find ways to increase efficiency or lower transportation costs. Or both.

Like race cars, trucks are often fitted with devices such as spoilers, ride skirts, or rear tail fairings to reduce drag and increase fuel efficiency. A recent report published by the University of Notre Dame offers a way to decrease drag and improve fuel efficiency without adding these bulky devices or substantial redesigning the vehicle.

University researchers, led by Thomas C. Corke, the Clark Equipment Professor of Engineering and Director of the Institute for Flow Physics and Control, studied a 1/12th scale model of a Class 8 truck trailer fitted with dielectric-barrier-discharge plasma actuators, simulating a full-scale truck-trailer combination approximately 55 ft. long, 13.5 ft. high, and 8 ft. wide, travelling at 65 mph. The purpose of the simulations was to see if, when placed on the model, plasma actuators would be effective in reducing the drag on the vehicle so air would flow along the top and sides of the tractor trailer in a more streamlined fashion.

Long story short, the results were very positive. The tests suggest a 22.7% drag reduction that would yield an 11% fuel savings at normal highway speeds.

The actuator technology, originally developed at Notre Dame by Corke and his team to reduce drag for wind turbines, has been licensed by Plasma Stream Technologies (PST) in Bettendorf, Iowa. PST is developing an actuator system specifically for trucks. Currently, the company is focused on the aft portion of a tractor trailer although plans are in the works for other areas of a truck, such as mirrors, under the cab, and the tractor-trailer gap.

How does it work? According to the company’s co-founder Pranay Bajjuri, a layer of dielectric material (plastic) sandwiched between two conductive tapes (aluminum) creates a plasma actuator. When a current is passed through a line of actuators placed on a vehicle, they produce a charged plasma, which then affects air flow. This changes the point at which the airflow detaches from a vehicle’s surface to become turbulent, reducing drag. The actuators can also be turned on and off as needed via an embedded network.




Bajjuri says that in addition to the increased aerodynamics, there are other benefits to the actuators. First, they would only require a 4-in. extension around three sides of the Class 8, so they would not need to be removed for loading or unloading. And at an average cost of about $2,500 per truck, the system PST is designing would provide a fuel savings of up to $10,000 per year per truck.

Product prototypes on several trucks is on track to be completed by February 2017 with full-scale production scheduled to begin by January 2018.

Corke and team has continued to enhance and develop this and other technologies to address flow control in aircraft in relation to drag and jet engines in relation to stall. To find out more about flow control research at Notre Dame, click here

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