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Scanning Technology Enables CFD at Reynard
Posted Mon November 25, 2002 @05:37PM
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Application The differences between motor racing on two wheels and four go far deeper than just arithmetic. In Formula 1, for instance, races are routinely won and lost in the pits; on motorbikes, the archaic practice of overtaking is still regularly reported. It is behind the scenes, however – away from the cameras – that the real differences between the two sports really emerge.

At any particular race, a Formula 1 car represents the current state of the art, a snapshot in an ongoing multimillion-pound research and development project. Teams recognize the importance of the most advanced design, simulation and testing techniques – and spend, spend, spend accordingly. The teams that race high performance bikes are every bit as keen to succeed but here the emphasis tends to be more on fine tuning and trimming rather than turning out machines that evolve steadily (sometimes dramatically) throughout a season.

Part of this is down to motorcycle racing’s rules and regulations: in some races every entrant must ride an identical bike, so room for design innovation is distinctly limited. And money is certainly an issue. The fact that individuals still race on a reasonably competitive basis with their more highly funded rivals is a reflection of the fact that cash is spread somewhat thinner than in Formula 1 racing.

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Whatever the reason, the fact remains that the emphasis in motorcycle racing is on finely tuned mechanics and rider skill rather than innovative electronics and exhaustive aerodynamic research, and some would say that they sport is the better for it. Specialists at Reynard Motorsport, the world’s leading manufacturer of race cars, however, believe that some of advanced techniques they use for optimizing car performance can have a significant role to play in the saddled sport, and are setting out to prove it to the motorcycle manufacturers.

Aerodynamicists are heavily reliant on computational fluid dynamics (CFD) techniques. Indeed, Reynard Motorsport has established a division – Advantage CFD – dedicated to nothing else. Dr Rob Lewis is the Divisional Manager. “We use CFD techniques to address some of the same issues that are dealt with in traditional wind tunnel testing, and have replicated real wind tunnel situations to verify that our results correlate well,” he says. “Because we make simplifications in the interests of speed we do not achieve 100 percent accuracy but we can quickly demonstrate the implications of design change and thus assist in optimization. Formula 1 car manufacturers recognize that a 2 or 3 percent performance improvement can make all the difference in a racing situation.”

As Lewis explains, CFD gains over wind tunnel testing in more than just time saving: “We can perform simulations that would be impossible with physical testing. In a wind tunnel, for example, you are basically restricted to a single car. Using CFD we can simulate a racing situation, determining the change in downforce when one car is tailing another.”

Advantage CFD works closely with its racing car clients, using specialist analytical techniques in the optimization of everything from nose cones to fuel tanks: here the right internal geometry can save vital fractions of a second during pitstop refueling. Approaches to motorcycle manufacturers, however, received a mixed response. “We were surprised at the range of commitment to aerodynamic analysis among bike companies,” says Lewis. “Most recognized that it had some value, but few believed that it could win them races. We were determined to change their minds.”

As with all CAE techniques, accurate geometrical representation is a prerequisite. As Lewis explains, however, this was a potential stumbling block for the motorcycle project: “We were in a bit of a Catch 22 situation. No bike manufacturer would take us seriously unless we could demonstrate the power of CFD analysis on a real bike, but there was no chance of them giving up their precious CAD data for the purpose. “To get the project off the ground we needed to find a way of generating accurate representative motorcycle geometry as quickly as possible,” he adds.

The closest thing to a racing bike that Advantage CFD could lay its hands on – very close, as it happened – was the Yamaha R1 owned by Adrian Reynard. As raw CAD geometry was unavailable, a reverse engineering route seemed to be the only option. The boss’s bike was therefore ridden (rather gingerly, no doubt) to the Coventry headquarters of 3D Scanners (UK) for a physical to digital makeover.

ModelMaker, the non-contact laser scanner from NVision-3D Scanners was used to reverse engineer the bike. “Although I know from past experience how accurate ModelMaker is, the priority for this job was to get a pretty good representation as quickly as possible,” explains Lewis. “There would have been no point at all in scanning a bike on its own – the rider is very much part of the racing geometry. This meant that someone had to be sitting on the bike in a convincing racing position for the duration of the scan. Realistically, this meant a number of discrete scanning sessions to avoid the ‘rider’ getting cramp, so without the speed of ModelMaker we could have been in for a long old haul.”

Scanning of bike and rider turned out to be well under a day’s work, and a workable CAD model was stitched together without trouble. This was surface-meshed in readiness for a series of CFD analyses.

The geometry was used as a basis for analysis in as close to a typical racing situation as possible. Because the bike was scanned in a static position the extension of the front suspension was unrealistic so this was tweaked before meshing; the wheels – naturally enough – were given a typical speed of rotation; the angle of attack was based on rounding a corner at pace. The results, including the spectacular trailing billows of dirty air, were exactly the kind of thing that Lewis needed to demonstrate the power of CFD in bike racing.

“I can see why motor cycle manufacturers might approach CFD with trepidation,” he says. “The flexibility of suspension and rider position means that geometry is changing constantly throughout a race, and a complete analysis would be impossible without CAD geometry and an in-depth understanding of rider dynamics. Even with the limited number of configurations we were able to estimate from our single scanning session, however, enough useful information could be gleaned to enable us to offer sensible advice.

“By varying the bike angle slightly and measuring the resultant forces, it is possible to get a quantifiable measure of stability,” he explains. “And in bike racing, stability – and therefore rider confidence – is probably the most important factor. A slower bike with a confident rider who is prepared to race aggressively can be a far more potent combination than a more powerful machine and a rider with the wobbles.”

Lewis is confident that in time CFD will become as important in two-wheeled motor sport as it is in four. “We have already been able to recommend design changes to bike companies, and it’s conceivable that the work we have been doing may even bring radical changes to the way that motorcycles are designed in the future,” he says. “Without the help of NVision-3D Scanners, though, we would have struggled to crack the chicken and egg situation of having no geometric data.” NVision-3D Scanners are the leading consultancy and solution providers in the field of non-contact digitizing. Their worldwide network allows them to draw on the expertise of hundreds of field specialists with a multitude of diverse experiences.

Velocity streamlines passing over a rider in a turn (view 1).

Velocity streamlines passing over a rider in a turn (view 2).

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