Case Studies

Streamlining Heavy Trucks for Better Fuel Efficiency

Contours November 2005 | Contributed by Craig Hunter SOLUS Solutions & Technologies | www.solusinc.com

Engineers and scientists at SOLUS are using Tecplot software to visualize the effectiveness of various drag reduction devices installed on heavy trucks in an effort to increase overall fuel efficiency. The plot represents surface pressures and field streamlines around the SOLUS-ODU representative heavy truck (RHT) model as computed by TetrUSS, a CFD software package originally developed by NASA. The CFD simulation was computed on a cluster of four dual-processor PowerMac G5 computers in May 2005. The simulation took 120 hours of computation time to complete.

The Researcher
Craig Hunter is lead engineer for CFD/Aerodynamics at SOLUS Solutions and Technologies, L.L.C., a service-disabled veteran-owned small business located in Virginia Beach, VA that provides expertise in aerodynamic, hydrodynamic, and flow control technology and solutions for the transportation industry. Founded in 1997 by president Richard Wood, the company is primarily focused on the development of cost-effective fuel economy improvement and emission reduction innovations for ground vehicles. The company is currently working under a grant from the U.S. Department of Energy (DOE) to advance the fuel efficiency of heavy trucks.

Solus/ODU Representative Heavy Truck (RHT), 25%-scale model mounted in the 30x60 foot Langley Full Scale Tunnel (LFST) for testing.
Photo courtesy of Old Dominion University

Reducing Drag on Heavy Trucks
In order to increase the fuel efficiency of heavy trucks, the SOLUS team is evaluating a number of patent-pending inventions installed on class 8 tractor trailer trucks in order to reduce aerodynamic drag. There are several areas on these big rigs that create airflow problems, making them less aerodynamic and thus decreasing their overall fuel efficiency. Engineers at SOLUS are using CFD technology coupled with Tecplot visualization capabilities to design, evaluate, and refine the effectiveness of several drag reduction devices.

Three SOLUS drag reduction devices were previously developed in a two-year operational road test and are currently being evaluated with CFD to refine the technology. Cross flow vortex trap devices, which resemble a series of vertical boards, are mounted on the front face of the trailer. These devices are designed to convert the cross flow in the gap between the truck and the trailer into a thrusting force. Vortex strakes are devices installed on the side and top of the trailer near the base to energize the flow behind the trailer where a big wake of air is created. In addition, an undercarriage device that looks somewhat like a mud flap, is installed under the trailer to control the flow behind the trailer.

Data obtained to date show that these three SOLUS devices improve the fuel economy of heavy trucks by 15%. CFD data will be coupled with information obtained from a follow-on multi-element experimental program led by Jeff Flamm, lead engineer responsible for experimental aerodynamics for SOLUS. This experimental program contains both wind tunnel testing and SAE Type II road tests that will be used to prepare the SOLUS technologies for the marketplace.

To ensure an accurate assessment of these devices, it was imperative that the CFD effort was performed on a realistic tractor trailer geometry. To address this critical requirement, the SOLUS team worked with partner Old Dominion University (ODU) and Great Dane Trailers to redesign a Department of Energy CAD model and add more realism to it. Kendrick Cary, a grad student at ODU, added wheel wells, tractor roof and side fairings, fifth wheel details, undercarriage structures, mirrors, beams, a c-channel along the top edge of the trailer box, brake and suspension components, landing gear used to prop up the trailer when it's unhitched from the truck, axles, and mud flaps to clutter up the model and make it more realistic. Hunter adds that they made the model as realistic as possible because, "If the trucking industry doesn't buy into it, then they won't really believe the results even if they are good results."

How Tecplot Helps Analyze the Options
After the CFD simulations were completed, Hunter, who has been a Tecplot user since 1993, used the Tecplot-format binary file created by TetrUSS to read data into Tecplot. He then set up a contour plot of pressure coefficient (Cp) on the truck surface and constructed surface streamlines on a plane at the truck centerline. The Tecplot visualization enables SOLUS to evaluate the effectiveness of each device, used alone and/or in unison with one another.

"Tecplot brings out the important 'qualitative' aspect of CFD, which relays a ton of important information about flow physics and aerodynamics," says Hunter. "We get a ton of information about the flow physics of the devices and details of the flow and at the same time, it allows us to evaluate things in a simpler environment."

In November, the team will take a 25% scale model of the same truck into the wind tunnel for physical testing. Though wind tunnel testing is valuable and necessary to the process, Hunter points out its shortcomings. "You can learn a lot in a wind tunnel test, but you can't really see the flow." He sees CFD and data visualization as an essential "screening" stage in the process that enables them to test out various devices before expensive physical tests are conducted. "With early screening using Tecplot, we can then reduce the number of things we need to test in the wind tunnel, so we can cut down on the cost and time involved."

All of the drag reduction devices being tested by SOLUS could eventually be used by the passenger vehicle industry as well. "A lot of the research work we do on heavy trucks could eventually trickle down to cars," says Hunter. "These concepts could work on SUVs and minivans, which are also kind of blocky and have the same sort of drag problems as heavy trucks."

Color contours of pressure coefficient shown on the crossflow vortex trap devices (left) and vortex strake devices (right).

Why Tecplot is the Visualization Tool of Choice at SOLUS
Hunter, who uses Tecplot to create contour, line plots, 2D contour, and 3D plots, says that life without Tecplot would be "complicated." He credits the software for its flexibility in handling many types of plots and datasets; its cross-platform availability and portability; and its ability to handle large datasets with ease.

"As the first visualization tool available for the Mac OS X operating system, it filled a critical need for us," says Hunter. "Tecplot combined with our other CFD tools has provided us with a full range of CFD analyses capabilities on Apple hardware. We also saved a lot of money by having a common UNIX hardware platform (desktop and laptop) that can support CFD preprocessing, computations, postprocessing, and still run off-the-shelf software like Microsoft Office."

Whereas many data visualization tools are focused on "niche" markets, Hunter believes what makes Tecplot different is that it offers "a wide range of capabilities while still being strong in key areas, such as CFD."

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