Cédric Touchette, holder of the Guinness record for fastest speed on a gravity-powered street luge (157.41 kmh/97.81 mph) decided to take up a new challenge: pass the symbolic mark of 100 mph, with no engine. Among the other thrill seekers interested in this challenge was Louis-Étienne Bouchard-Pouliot, an account manager at Creaform Inc., developer and manufacturer of portable 3D measurement technologies.
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“Our luge team, the 3 Bobs, broke the world speed record in September 2008, and we came very close to the 100 miles per hour [mark] at that time,” says Bouchard-Pouliot. “Since then, we have tweaked our gear, but we had a hard time figuring out how to improve the aerodynamics of our luges to gain even more speed.”
CFD pushes back the speed limits in street luge
Bouchard-Pouliot and his teammates asked Creaform’s digital simulation team to help them out. The goal: using computational fluid dynamics (CFD) to simulate air flows to reduce the aerodynamic drag and break their very own speed record.
Step 1: 3D scanning
To digitally simulate flows, you first need a computer model of the object. In this case, a representation of the surfaces in contact with air was the only thing required, and so it was essential to get the exact 3D reconstruction of the luge racer in sliding position. This was done quite easily with a Handyscan 3D handheld portable scanner, developed by Creaform. The surface mesh it generated was transferred to the digital simulation team.
Step 2: Fluid mesh
The surface mesh is used as a starting point to define the air volume around the object to be analyzed, and it is later divided into several small elements: This is the fluid mesh. In this case, the file was made of 3 million elements. Using physics laws called the Navier-Stokes equations, the flow characteristics such as speed, pressure, temperature, and turbulence level have been calculated for each of these elements.
Step 3: Analysis and recommendations
This provides info on the flow behavior on any point of the calculation volume, which makes it possible to calculate with precision the aerodynamic shapes on the body, as well as the air particles.
“By calculating the CFD from the real scanned geometry, we were able to identify several ways to increase the top speed,” explains Creaform fluid dynamics specialist, Steve Julien. “We found that with a new profile on the rear of the luge and by modifying the position of the luge racer, it was possible to limit the zones of high pressure while reducing the flow recirculation zones. We also found out that the suit created a lot of rugosity at the legs and increased unnecessary chafing. Thanks to the modifications that we have made, we were able to easily gain between 5 to 10 km per hour. The high-accuracy scanning file generated with the Handyscan 3D portable scanner turned out very helpful, as it provided us with a wealth of information that we would not have had otherwise.”
Step 4: Let’s break that record!
On June 18, 2012, current Guinness record holder Cédric Touchette was lying on his new and more aerodynamic luge, ready to rush down the famous Éboulements hill, located in the Charlevoix area, in the province of Quebec, Canada. During a practice run before the race, which was officially monitored by the Guinness records organization, mechanical issues arose.
“The wheels started to vibrate and my luge to wobble,” says Touchette. “I got pulled off to the left, and I saw the concrete wall coming in on me. When you’re rolling that fast, it is really scary! I’m done chasing records for now!” During that “slow” practice race, the thrill seeker still peaked at 152 km/h.
“I’m still convinced that the new luge could break the record,” insists Julien. “But I’m not reckless enough to throw myself down that hill to prove it!”
CFD in a nutshell
In a true virtual laboratory, CFD makes it possible to analyze, design, and optimize any system involving a liquid or a gas. You can:
• Detect an issue before it arises or correct and existing problem
• Get a better physical understanding of the system
• Test the operating conditions and validate new concepts
This powerful engineering tool—CFD—helps in reducing costs and development cycles while improving the quality and reliability of the products.
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