As the 2012 Tour de France gets underway and the Summer Olympics prepares to kick off in London, competitive cyclists could benefit from the results of a new Computational Fluid Dynamics (CFD) study that focuses on optimizing the position of cyclists on bikes to reduce drag.
The study, conducted at the Eindhoven University of Technology in The Netherlands and led by Bert Blocken, professor in Urban Physics, leveraged ANSYS CFD software to analyze the drafting effects of cyclists in more detail.
It is well-established in cycling circles that drafting riders (cyclists who ride behind another rider) benefit from the slipstream of the front rider, reducing air resistance of about 30 percent to 35 percent for the second rider. While there has been consensus around this finding, there are no published definitive studies on real cyclists examining air resistance on the leading rider -- a gap in research that prompted Blocken and his team to pursue the CFD study on their own.
A CFD study on the drafting effects of cyclists shows that leading riders can achieve a 2 percent to 2.5 percent reduction in drag. (Source: ANSYS, Eindhoven University of Technology)
In 2006, Blocken's team had been commissioned by the Flemish cycling union to explore a similar study on optimizing aerodynamics for a single cyclist. With help from a team at KU Leuven, Blocken's group laser scanned a cyclist's body and created a CFD model, exploring flow and aerodynamic resistance in a virtual wind tunnel as opposed to the traditional field and wind tunnel testing, which can be time-consuming and expensive.
Building on that early research, the team created a new model incorporating multiple cyclists' bodies riding behind each other. This effort marks the first time a detailed CFD study has been announced on airflow around actual cyclists as opposed to previous studies that were predicated on flow around simple cylindrical geometries, Blocken told us.
Well, this is great work. It is an interesting use of CAE to understand what is really happening in a sport. A lot of this type of study is done in swimming.
The only reservation I have is that it makes the whole thing more complicated. It will increase the cost of fielding a team since they will now have to purchase the CAE software and all the equipment for measuring athletes.
That is if the racing teams actually make an investment in this kind of research, but you're right. It does inject a level of complexity and cost into the equation. Then again, competitive sports teams make this kind of investment all the time. Professional football teams do all kinds of analysis and simulation, golf professionals do, and the list goes on.
Yes, it make it more complicated, but this type of complication is usually welcomed in competitive sports. Part of the competition is off-road, where teams study everything little item that can afford an advantage.
I was involved in the controls for a new soft drink bottling line last year. It was fascinating to watch 2-liter bottles move from the blow-molder to the filling machine on air-veyors. The bottle is supported by its neck, and the air-veyor blows air downstream, providing an almost frictionless conveying means. The bottles move very fast.
While the transport alone was neat to watch, the fascinating part was what happened to the bottles. Trailing bottles would catch up to the one in front of it, until about 6-8 bottles were moving along in a single slug. Physics and geometry created that optimum slug. No other bottles could catch up to it, so another slug would form behind it.
I would imagine there is an optimum cycle train as well, for a given average cyclist mass, speed, and cross-sectional area, not just the benefits of a pair of riders. That would seem to be the next path to explore.
Thanks for the question. We never counted the hours, but we have been working on the aerodynamics of single (isolated) cyclists since 2006. This studied was funded by the Flemish Cycling Union. It was a full-time job performed by postdoctoral fellow Erwin Koninckx for one year and a half. Also Thijs Defraeye (PhD student at the time) worked for almost 50% of the time during more than two years on this project. Both were supervised by Peter Hespel, Jan Carmeliet and me. Erwin was later hired by the Flemish Cycling Union and is working there now. Erwin was/is the perfect man for the job: he has a double master degree, one in engineering and one in biomedical kinesiology, as well as a PhD in biomedical kinesiology.
The second study, i.e. on the groups of cyclists, was started in 2009. I started this study as a personal initiative because I wanted to investigate what would happen with groups of cyclists. There was no funding for this initiative, but luckily I could count also on the enthusiasm and support from the previous collaborators: Erwin, Thijs, Peter Hespel and Jan Carmeliet. Also the wind tunnel team at Dutch-German Wind Tunnels was enthusiastic and gave us some free testing time. This study - with some interruptions due to other tasks - is still going further today. I think I have spent, overall, more than 6 months full time on this second study. But much of this was spread over the past three years, including many weekends and evenings. Although our computing cluster has been calculating almost continuously in the past 10 months, and is still doing so today.
Thank you for the comments and thanks Beth for the very nice article about our work. Here, I would like to acknowledge the other members of the team:
- Dr. Thijs Defraeye, Leuven University, Belgium - Dr. Erwin Koninckx, Flemish Cycling Union, Belgium - Prof.dr. Peter Hespel, Bakala Academy - Athletic Performance Center, Leuven University, Belgium - Prof.dr. Jan Carmeliet, ETH Zurich, Switzerland
Thanks for the update on the project and for sharing your work with us. Very, very interesting and sounds like there's more to be done. Can you give us an idea of what kind of computing cluster is churning through all these calculations over the last six months?
Hi Beth, the computations are performed by parallel processing on twelve HP DL360R07 Xeon X5650 2.66 GHz processors with 96 Gb RAM, although the full range of RAM memory has not been needed yet for this study - this will only be needed when we extend the group of cyclists to about 15-20.
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