The top prize in NASCAR racing is the Winston Cup, and the current cup-holders, Joe Gibbs Racing, work very hard to stay at the top. Maybe you've seen them flashing across your TV set on a recent Sunday—the #18 car driven by Bobby Labonte, and the #20 car driven by Tony Stewart.
CFD simulation of an intake valve in a Joe Gibbs Racing NASCAR design, showing streamlines and pressure contours.
The team gets design help in the form of sponsorship by SDRC (Milford, OH, now called EDS PLM Solutions) and Hewlett-Packard (Palo Alto, CA)—who provide I-DEAS software and HP workstations and laptop computers. The designers also use Fluent, for computational fluid dynamic (CFD) analysis.
"The biggest challenge is time," says Todd Meredith, chief engineer for the team. "Anything that increases productivity is a big benefit, because something always needs to be improved, and as the work progresses, you have to work harder and harder to make components better."
Unlike Formula One and CART cars, for which designers bolt a complete engine onto an ever-evolving chassis, NASCAR cars are subject to ongoing design improvements for both engine and chassis. Designers and builders use standard components that they then assemble and modify, and because every team starts out with nearly identical pieces, each has to work very hard on customization to gain an advantage.
With all this customization, designing a new vehicle for NASCAR racing can take more than a year. Other design jobs, however, have to be completed in days. "If a part fails in a race on Sunday, it has to be fixed and improved by the time the car gets shipped to the next race on Thursday," Meredith says.
One way they accelerate their design speed is by using I-DEAS to simulate potential failure points with FEA. Despite this speed advantage, the team depends on laboratory testing far more than on computer simulation. "The labs look at parts that failed with electron microscopes and may find a tiny nick in the metal that caused the failure, something FEA can't do," he adds.
In their search for faster track speed, Charles Jenckes performs CFD on the designs. "We use CFD for internal studies of fuel and air flow in the engine, as well as external aerodynamics," he says. The studies follows the velocity and pressure gradients of both air and fuel as they pass through the air-box, carburetor, intake manifold, cylinder head, and out the exhaust. "We can use this information to improve the flow of both," Jenckes says. "We also analyze coolant flow through the engine."
When it comes to external fluid dynamics, Jenckes uses Fluent to study under- and over-body flow. "The results are more comprehensive than physical wind-tunnel tests," he says, "because CFD lets you rotate the wheels and move the road, so you can look at the pressure gradient over the whole surface instead of selected points, as you have to do in physical tests."