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Metrology

3-D Scanning Helps NASCAR Cars Gain That 0.1 MPH Edge

Controlling aerodynamic design using Rapidform XOR

Published: Wednesday, June 22, 2011 - 06:00

Cars scream around the track at speeds approaching 200 mph, yet a 500-mile NASCAR race can be decided by a few tenths of a second. To be a winner, NASCAR teams seek any advantage they can create. However, NASCAR has strict guidelines that specify nearly every aspect of the “stock” car. For BMI Corp., experts in computational fluid dynamics (CFD) analysis, designing the most aerodynamic cars that conform to NASCAR’s restrictions means using leading-edge technology. A crucial part of BMI’s technological arsenal is Rapidform XOR.

BMI co-founder Michael Henderson provides the expertise behind the company’s aerodynamic advantage. Henderson spent 32 years with Boeing, mostly as head of research, and he led the company’s early work with CFD. For Henderson, who is also involved in developing a supersonic business jet, there is little difference between aircraft and race cars in terms of aerodynamics. While race cars are far from supersonic, Henderson believes that aerodynamic excellence will break a few barriers.


CFD simulation

“CFD is a critical tool for refining cars racing in a NASCAR series,” says Henderson. “It helps us to visualize the changes that will translate to more speed. Other teams rely on wind tunnels, but the results are inaccurate. Interaction with the floor, walls, and ceiling can throw measurements off by 20 percent.” Some teams are adopting in-house CFD; however, according to Henderson, “Our edge is the expertise in performing CFD simulations and interpreting the results.” Expanding this expertise, Henderson’s latest hire was John Anastos, an aerospace engineer with a background in CFD. Anastos supports BMI through its sister company, Advanced Vehicle Research (AVR) based in Greenville, South Carolina. AVR performs aerodynamic analysis for NASCAR teams, as well as the Indy Racing League (IRL) and Formula 1 teams.

At AVR, Anastos’ technology includes Rapidform XOR, a Konica Minolta laser scanner, and two sophisticated CFD software programs that Henderson used at Boeing. The laser scanner produces point clouds that define the entire car, including the undercarriage, and Rapidform processes the point clouds to produce surface data that fuels the CFD programs.

“The 3-D scanning process is essential because each car is unique; they are basically handmade,” says Anastos. He also noted that scanning the undercarriage is critical in the analysis because this is where downforce is created. “We tune the car’s design to accelerate airflow along the undercarriage. It acts like a plane’s wing, only in reverse.”

According to Anastos, AVR looks for minor adjustments, some almost undetectable, that yield an increase in available horsepower. “With NASCAR’s stringent rules, cars are closely matched, so these small changes can be the difference between winning and losing,” says Anastos. NASCAR’s templates give teams only 0.070 in. to 0.50 in. design latitude. “On a track like Atlanta Motor Speedway, a 5-percent decrease in drag is the equivalent of a 25-horsepower (hp) gain, which gives an increase in lap speed of 0.5 mph,” says Anastos. “On the same track, a 0.1 increase in downforce coefficient gives an increase in lap speed of 1.8 mph. It would take a 70 hp gain to get the same results.”

“Without a smooth, precise 3-D definition of the car, our CFD results would not be accurate enough to detect these fine adjustments,” says Anastos. To capture every detail of the car, AVR will do 150 laser scans, which takes eight to 10 hours. In that time, the laser scanner will collect nearly 20 million points for a typical car. Once scanning is complete, Anastos brings the point clouds into Rapidform, where he filters the data to remove noise, artifacts, and redundant points. This reduces the point clouds to 5 million data points.

Anastos uses Rapidform to align the individual scans to one another and merge them into one data set. “As I am merging, I use Rapidform’s Accuracy Analyzer to check that the overall dimensions accurately reflect the car,” explains Anastos. He then deletes markers, fills gaps in the point cloud, and massages the 3-D data. “During this step, I really enjoy the automated processes that the software offers. For example, the one-button healing function, which checks and repairs defects in the scan data, is huge. It saves me so much time; I don’t know what I would do without it.” Anastos notes that Rapidform is very comprehensive yet simple to learn. “With a background in CAD, Rapidform is rather intuitive. I found it very easy to learn, and it does everything I need it to do,” he says.


CFD-ready models created with Rapidform’s surfacing tools

Anastos builds the CFD-ready model with Rapidform’s NURBS surfacing tools. Since these Rapidform data are parametric, he can easily edit the model at any point in the process. When surfacing is completed, he imports the model into the CFD program.

AVR starts with an analysis of the car’s shell, using CFD to seek the small changes that yield performance gains. They then begin adding parts, such as tires, spoiler, and undercarriage, and repeat the analysis with each addition. “We do the build up so that we can see the incremental changes and the cumulative effects of each part of the car,” says Anastos. Once AVR achieves optimal drag and downforce, the car goes to the test track or wind tunnel to confirm the analysis. “Others start with the wind tunnel. We turn the process upside down,” says Anastos.

With the introduction of the Car of Tomorrow (COT), which NASCAR designed to make racing safer, more competitive, and cheaper for the race teams, AVR’s challenges increase. NASCAR’s changes make the cars less aerodynamic, and templates are more stringent. Anastos said, “For the Car of Tomorrow, we will be playing with flow on the undercarriage,” says Anastos. “This is where the race will be won.”

Whether it is the current templates or those of the COT, AVR is using 3-D scanning and CFD to help NASCAR race cars fly like the wind.

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About The Author

Rapidform Inc.’s picture

Rapidform Inc.

Rapidform Inc. is the U.S. subsidiary of INUS Technology Inc., which develops and markets the world’s most advanced 3-D scan data processing software solutions. These solutions are the most widely installed products for reverse engineering and inspection of 3-D scan data in the world and are used in design, manufacturing, research and development, quality inspection, medical research, and civil engineering. Clients include Audi, Ford, Hyundai, Toyota, Rolls Royce, Volkswagen, Hitachi, Panasonic, Samsung, Sony, and more. Rapidform Inc. has offices in Lakewood, Colorado, and Newark, California. INUS Technology is headquartered in Seoul, Korea.