SOLUS Solutions and Technologies is a Virginia-based research consultancy that provides expertise in aerodynamic, hydrodynamic, and flow control technology and solutions for the transportation industry. Founded in 1997, the company is primarily focused on the development of cost-effective fuel economy improvement and emission reduction innovations for ground vehicles.

In order to increase the fuel efficiency of heavy trucks, researchers are SOLUS are testing how various devices installed on trucks could help reduce overall drag. There are several problem areas on these big rigs that create airflow problems, making them less aerodynamic and thus decreasing their overall fuel efficiency. Researchers at SOLUS are using CFD technology coupled with Tecplot visualization capabilities to test and evaluate the effectiveness of several drag reduction devices.

The Tecplot CFD visualisation enabled SOLUS to evaluate how effective a number of devices installed on trucks could help reduce overall drag.

Three drag reduction devices are currently being tested by SOLUS. 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 control the airflow that might get trapped in the gap between the truck and the trailer. Vortex strakes are devices installed on the side, back and top of the trailer 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.

To test these devices, researchers performed CFD simulations on a generic truck model provided to them by the DOE. Since the truck model had been criticised by the trucking industry for being too simplistic, Craig Hunter, vice president of CFD/Aerodynamics for SOLUS, and his team reworked the original CAD model to add more realism to it. They added beams; a c-channel along the top edge of the trailer box; brake and suspension pieces; 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.”

Analysing the options

After the CFD simulations were completed, Hunter, who has been a Tecplot user since 1993, used the .plt binary file created by TetrUSS, a CFD software originally developed by NASA, to read into Tecplot. He then set up a contour plot of pressure coefficient (Cp) on the truck surface and constructed surface streamlines on a plan at the truck centreline. The Tecplot visualisation enables them to evaluate the effectiveness of each device, used alone and/or in unison with one another.

The plot represents surface pressures and field streamlines around the SOLUS-ODU representative heavy truck model as computed by TetrUSS. 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.

“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 late November, the team will take a 1/4 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 visualisation 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.”

Many of the drag reduction devices currently being tested by SOLUS researchers 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. “A lot of these concepts could work on SUVs, minivans, which are also kind of blocky and have the same sort of drag as heavy trucks.”

The clear picture

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 visualisation 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 visualisation 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.”