11/17/13 Digital Manufacturing Report: Capturing the Unicorn: The Lure of Affordable High Tech Bike Racing Wheels www.digitalmanufacturingreport.com/dmr/2013-01-18/capturing_the_unicorn:_the_lure_of_affordable_high_tech_bike_racing_wheels.html?layout=print 1/3 Capturing the Unicorn: The Lure of Affordable High Tech Bike Racing Wheels January 18, 2013 | John Kirkley Last week we wrote a feature story about the use of computational fluid dynamics (CFD) in the design of bicycle racing wheels. Here’s a companion piece, this time featuring FLO Cycling, one of those small- to medium-sized manufacturers (SMMs) that have been dubbed the “missing middle.” Missing middle SMMs have yet to adopt advanced digital manufacturing techniques. FLO is far from missing. In fact, the two-year old company is an avid user of CFD. According to a write up by Justin Smothers, JCS Engineers, Jon Thornham and Chris Thornham, FLO Cycling, and Prashanth Shankara, CD-adapco, FLO Cycling has leveraged CFD to bring to market what has been dubbed the “mythical unicorn” of the bike racing world – a high-performance, superior, aerodynamically designed bike wheel at an affordable price. A Matter of Money Here’s the problem. Well engineered, high-end bike wheels are expensive – often costing several thousand dollars. At the other end of the spectrum, affordable wheels, although well manufactured are minimally engineered and offer a much reduced level of performance. FLO’s target market consists primarily of triathlon racers and cyclists. They can be just as demanding as the pros. However, most of them can’t afford the high-priced competitive wheels, but still want top performance from their lower cost models. To meet these requirements, FLO cut some of their production costs by fine tuning their marketing and distribution strategy by selling direct to the customer. But a major factor in collaring the mythical unicorn has been the use of modeling and simulation in the form of CFD and wind tunnels in the development process. The CFD software used by FLO is CD-adapco’s STAR- CCM+. Most bicycle wheel manufacturers employ the V-notch or the Toroidal Fairing configuration for designing competitive racing wheels. The V-notch has low aerodynamic drag but can be unstable in crosswinds because of asymmetry between the front and rear half of the tire. The Toroidal Fairing provides better crosswind stability compared to the V-notch. Side winds create a complex aerodynamic situation including a yaw angle at the leading edge of the wheels,
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11/17/13 Digital Manufacturing Report: Capturing the Unicorn: The Lure of Affordable High Tech Bike Racing Wheels
Capturing the Unicorn: The Lure of Affordable High Tech BikeRacing WheelsJanuary 18, 2013 | John Kirkley
Last week we wrote a feature story about the use ofcomputational fluid dynamics (CFD) in the design of bicycleracing wheels. Here’s a companion piece, this time featuring FLOCycling, one of those small- to medium-sized manufacturers(SMMs) that have been dubbed the “missing middle.” Missingmiddle SMMs have yet to adopt advanced digital manufacturingtechniques. FLO is far from missing. In fact, the two-year oldcompany is an avid user of CFD.
According to a write up by Justin Smothers, JCS Engineers, JonThornham and Chris Thornham, FLO Cycling, and Prashanth Shankara, CD-adapco, FLO Cycling has leveraged CFDto bring to market what has been dubbed the “mythical unicorn” of the bike racing world – a high-performance,superior, aerodynamically designed bike wheel at an affordable price.
A Matter of Money
Here’s the problem. Well engineered, high-end bike wheels are expensive – often costing several thousand dollars. At the other end of the spectrum, affordable wheels, although well manufactured are minimally engineered andoffer a much reduced level of performance.
FLO’s target market consists primarily of triathlon racers and cyclists. They can be just as demanding as the pros.However, most of them can’t afford the high-priced competitive wheels, but still want top performance from theirlower cost models.
To meet these requirements, FLO cut some of their production costs by finetuning their marketing and distribution strategy by selling direct to thecustomer. But a major factor in collaring the mythical unicorn has been theuse of modeling and simulation in the form of CFD and wind tunnels in thedevelopment process. The CFD software used by FLO is CD-adapco’s STAR-CCM+.
Most bicycle wheel manufacturers employ the V-notch or the Toroidal Fairingconfiguration for designing competitive racing wheels. The V-notch has lowaerodynamic drag but can be unstable in crosswinds because of asymmetrybetween the front and rear half of the tire. The Toroidal Fairing providesbetter crosswind stability compared to the V-notch.
Side winds create a complex aerodynamic situation including a yaw angle at the leading edge of the wheels,
resulting in side forces that have to be taken into account in the wheel design. During side winds, the design of theleading edge of the back of the wheel also impacts aerodynamics.
Using CFD as part of the design process, FLO has created a rounded-edgeback wheel to deal with this problem. The company’s wide fairing designprovides a nearly identical front and rear half of the wheel. The rounded rearedge closely matches the profile of the tire, rather than presenting a pointedrear half. The result is greater crosswind stability and excellentaerodynamics.
FLO also applied something called Net Low Drag Technology. Most currentracing wheels provide low drag and fast speeds at one particular yaw angle. But in a race, yaw angles can vary from 10 to 20 degrees. FLO’s designsensure the fastest speed at all yaw angles between 12 and 20 degrees.
The optimum rim and fairing shapes were selected based on CFD results. To really be effective, CFD should beused from the very beginning of the design process. This allows the engineers and designers to try out a widevariety of shapes and solutions to determine what geometries produce the optimum results. Then they canperform the more expensive wind tunnel tests on a few of the most promising solutions. When the best design hasbeen selected, the next step is to send CAD drawings to a mold maker who creates a set of custom molds. Thewhole point is to design and refine the rim shape for optimal aerodynamics before a mold is opened.
The CFD Exper ience
To come up with the designs for their innovative wheels, FLO mad full use of CFD to determine the final fairingdesign. First a variety of fairing shapes based on the FLO wide Toroidal wheel were created in a CAD environment. These shapes were analyzed using STAR-CCM+ and tested for a wide variety of race conditions, including windspeeds ranging from five to 30 mph, and yaw angles from zero to 20 degrees.
The designers created a polyhedral mesh with 1.5 million cellsfor the CFD analysis. This included a prism layer mesh tocapture the boundary layer flow on the wheel. They also usedthe CFD software’s volumetric refinement feature to createlocal refinement zones around the wheel so they could analyzethe wheel’s wake.
The designers were able to change the wind speed and yawangles for each iteration of the design. Simulations were run ona single core over a period of 28 days – a supercomputerwasn’t necessary (although the authors admit that the extracompute power would have gotten the job done faster).
11/17/13 Digital Manufacturing Report: Capturing the Unicorn: The Lure of Affordable High Tech Bike Racing Wheels
CFD also allowed the engineers to cut down on wind tunnel tests, saving money and speeding up the designprocess. The chart compares the drag force from CFD simulation and wind tunnel for the FLO 60 final prototype. The numerical results gave the engineers invaluable insights into the wheel’s behavior before testing a singleprototype in the wind tunnel.
When the wheel finally made it to the wind tunnel, and there were no surprises – the CFD analysis had paved theway for successful physical prototype testing.
And, in the process, FLO made the “mythical unicorn” a reality.
