During the big Tour de France time trial on 15 July, Tom Dumoulin will be cycling in a new skinsuit, jointly developed by Team Giant-Alpecin and the TU Delft. The university applied an innovative method to research the aerodynamics of the suit: Dumoulin’s body was first scanned, after which a 3D mannequin of his body was printed. The drag of this mannequin – each time with a different suit – was then tested and optimised in the TU Delft’s wind tunnel.

Precise measurements

One of the areas where professional cyclists can still make a difference is (even) better aerodynamics. This is partly determined by the cyclist’s posture on the bike, but a more streamlined outfit can also play a part. Reason enough for Team Giant-Alpecin to collaborate with TU Delft scientists on developing an improved cycling suit. ‘It’s split seconds that count in cycling, especially during a time trial , so if a faster suit can deliver only a small improvement, this can still make the difference’, according to Tom Dumoulin. After all, the margin between Tom Dumoulin and the runner-up in the prologue of the Giro d’Italia was a mere twenty two thousandths of a second.

Scientifically speaking, you’d ideally have unlimited access to the athlete, in order to conduct extensive wind tunnel tests and develop the perfect suit for them specifically. However, you can’t place a professional cyclist in a wind tunnel for weeks on end. The consequent idea developed at the TU Delft was to not place the cyclist himself, in this case Tom Dumoulin, in the wind tunnel, but a mannequin with the exact same physical measurements. An even more important upside to the use of a mannequin in the wind tunnel: it remains perfectly still, so measuring the airflows around the body becomes much quicker and more accurate.   

Tour de France Time Trial

The project is aimed at the time trial outfit for Tom Dumoulin, one of the best time trial cyclists in the world. The new and improved suit will be used during the big time trial on the 15 July in the Tour de France. ‘It took several steps to make the suit more aerodynamic. First, Dumoulin’s body was accurately scanned. Next, using this data, a precise, full-size mannequin of his body was 3D printed. This mannequin was then used to take measurements with different suits and materials in the TU Delft wind tunnel’, explains Dr Daan Bregman of the TU Delft Sports Engineering Institute.

A 3D printed mannequin of Tom Dumoulin in the wind tunnel helps gain a competitive advantage

Scanning Tom Dumoulin

Dr Jouke Verlinden of the Faculty of Industrial Design Engineering at the TU Delft was mainly concerned with developing a good mannequin. ‘Step one in this process is the accurate scanning of the cyclist. We outsourced this task to a specialised company  – th3rd – who use a photogrammetric method. In short, we used 150 DSLR cameras to take a lot of pictures of the body from many different angles, all at the same time. Tom Dumoulin was ready in 30 minutes or so, but for us, the work had only just started.’

‘As a result of all those digital images, we were left with huge amounts of data. It’s key to use the data correctly, for example by splitting up the files in a smart way: the so-called 3D segmenting. You should also determine where the accuracy of the scan and the resulting print is somewhat less important. In those areas you can strongly reduce the amount of data you need. If you aim to make a model that is accurate to the micrometre throughout, you’ll end up spending way too much time printing the mannequin.’

Scannen Tom Dumoulin, Foto: Mark de Swart

 

3D-printing the mannequin

The next step in the process is building the mannequin – for which 3D printing was chosen. ‘3D printing is getting increasingly accurate and cheap and thus more attainable. We actually use a fairly standard 3D printer, albeit one that can print relatively quickly. With a relatively simple adjustment, the printer can now reach up to 2 metres high. It took us about 50 hours to print the mannequin up to 20 micrometres precise. The method we used is called Fused Deposition Modelling, in which the model is built up in plastic layer-by-layer.’

TU Delft -printing head Tom Dumoulin

‘Incidentally, we printed the mannequin in eight separate parts, using multiple printers at a time. Don’t forget, the parts should be able to move with respect to each other to get the mannequin on the bike in a realistic posture. And of course, it should also be possible to change the mannequin into a new suit. The eight parts are attached to one another via simple pin-and-hole joints.’

3-D geprinte mannequin Tom Dumoulin in tijdritpositie
Foto Cees Vos | Team Giant-Alpecin

 

To the wind tunnel

The mannequin of Dumoulin then went to Wouter Terra, a PhD-student at the Faculty of Aerospace Engineering at the TU Delft. He took several measurements in the TU Delft wind tunnel, using different suits and materials. ‘You would expect a smoother fabric to induce less drag’, explains Terra. ‘But this isn’t always the case – especially when looking at the airflow around a rounded blunt, non-streamlined shape, like the body of a cyclist.’ Why does a ridged surface perform better in certain areas? ‘In short, it boils down to this: drag is built up out of two components. First, the drag through friction and second, the drag through pressure’, explains Terra. ‘Through the roughness of the ribbed pattern, the drag through friction will increase, but the drag through pressure can drastically drop. The net drag will then decrease. An inventive combination of rough and smooth spots on the suit might only result in a decrease in drag of half a percent, but this could potentially deliver those precious seconds that make the difference between winning or being in the top 10’, is the PhD student’s assessment.

‘Because research has shown that the composition and structure of the fabric in a cycling suit have a significant influence on the drag, we started exploring how to improve our time trial suit’, explains Teun van Erp, scientific expert of Team Giant-Alpecin.

Cylinders

‘We started off by testing all available fabrics from Etxeondo (Team Giant-Alpecin’s clothing supplier) in the wind tunnel on a cylinder – the upper arm, lower leg and upper leg bear a close resemblance to this shape’, says Terra. ‘This provided us with a good insight on the fabrics we could best use for the various body parts.’ The aerodynamics experts then built several suits with the best performing fabrics, using variations in roughness and patterns, after which they were tested for drag on the Tom Dumoulin mannequin in the wind tunnel. The method used for mapping the airflows is also quite special. PIV (Particle Image Velocimetry) was used: the movement of small particles in the airflow is analysed to get an overall view of the current. ‘To research on the scale of a cyclist, we added an innovative technique to this method; helium-filled soap bubbles were used to map the current and ensure good measurements.’

Windtunneltest met PIV technologie
Foto: Cor Vos | Team Giant Alpecin

 

Time savings

Terra expects Tom Dumoulin’s new time trial outfit , that was in part based on the insights from the TU Delft wind tunnel tests, to result in a time saving. ‘We measured a clear difference in drag between the various materials. A difference of just one percent in drag, to name but a number, might not seem much, but can result in a time saving of about ten seconds in a hour-long time trial.

‘On top of this, you could imagine that cycling in an improved suit can also have a psychological effect on the athlete’, says Teun van Erp (Team Giant-Alpecin).

Long-lasting collaboration

‘The beauty of this project lies in the interdisciplinary nature of it’, says Daan Bregman of the TU Delft Sports Engineering Institute. ‘Without all the knowledge from various disciplines, we would have never been able to execute it so well.’ 
‘We have a lot of fundamental scientific knowledge on offer and our aim is to apply this to sports in many disciplines. Cycling is one of those areas. About a year and a half ago, we came into contact with the Team Giant-Alpecin, a professional cycling team very open to increase the scientific contribution in the domain of cycling, in order to improve their performance even more.’

Team Giant-Alpecin and the TU Delft have recently announced a long-lasting collaboration. Meanwhile, this collaboration has reached four key areas, one of which is aerodynamics.

More information:

High res photo's download link (credits as above)
PIV technology TU Delft
Press release Team Giant-Alpecin on the collaboration with the TU Delft
Team Giant-Alpecin presents innovations for the 2016 Tour de France
Press release TU Delft on the collaboration with Team Giant-Alpecin