TU Delft Wind Tunnel Project To Gain Aaro Advantage In Tour De France & Beyond

The difference between winning and losing can come down to the smallest details - consider the margin between Tom Dumoulin (NED) and the runner-up in the prologue of the Giro d’Italia with a mere twenty two thousandths of a second. 

Team Giant-Alpecin’s experts have been working with Delft University of Technology (TU Delft) and the team’s premium clothing partner, Etxeondo, on a project to make the team’s fast time trial suit even faster using a 3D printed mannequin of Dumoulin. Tomorrow, the skin suit will make its competition debut during stage 13 of the Tour de France, the 37.5km individual time trial.
 
The aerodynamics project
One of the areas where professional cyclists can still make a difference is aerodynamics, reason enough for Team Giant-Alpecin to cooperate with TU Delft scientists to make their fast time trial suit even faster. "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 will make the difference," said Dumoulin.

Scientific expert of Team Giant-Alpecin, Teun van Erp (NED) explained: "Research has shown that the composition and structure of the fabric in a cycling suit have a significant influence on resistance and drag, important for us to start exploring how to further improve our time trial suit". 

Together with the team, the university applied an innovative method to research the aerodynamics of the suit. Dumoulin’s body was first accurately scanned, after which a precise, full-size mannequin of his body was 3D printed. The drag of this mannequin – each time with different fabric types – was then tested and optimised in the TU Delft’s wind tunnel using the university's unique PIV (Particle Image Velocimetry) technique.

About using a mannequin, Dr Daan Bregman (NED) of the TU Delft Sports Engineering Institute, explained: "Scientifically speaking, one ideally has 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 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."

Video: TU Delft wind tunnel project to gain aero advantage with 3D printed mannequin of Tom Dumoulin.

Scanning Tom Dumoulin Dr Jouke Verlinden (NED) of the Faculty of Industrial Design Engineering at the TU Delft was mainly concerned with developing the 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. 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."

3D-printing the mannequin The next step in the process is building the mannequin – for which 3D printing was chosen. Verlinden said: "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. We printed the mannequin in eight separate parts, using multiple printers at a time."

To the wind tunnel The mannequin of Dumoulin then went to the wind tunnel, where several measurements have been conducted, using different suits and fabrics. This is the point where the expertise of the team's high-end clothing partner, Etxeondo came into the project. Wouter Terra (NED), PhD-student at the Faculty of Aerospace Engineering at TU Delft explained: "We started off by testing all available fabrics from Etxeondo in the wind tunnel on a cylinder – the upper arm, lower leg and upper leg bear a close resemblance to this shape. This provided us with a good insight on the fabrics we could best use for the various body parts. "The next step was to built several suits with the best performing fabrics, using variations in roughness and patterns, after which they were tested for drag on the 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."

"You would expect a smoother fabric to induce less drag. 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’, explained 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."

Time savings Terra expects Dumoulin’s new time trial suit, 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," added van Erp. "Not only Dumoulin, but also our GC contender in the Tour de France, Warren Barguil (FRA) will use the new time trial suit on stage 13 and beyond."

Long-lasting partnership Team Giant-Alpecin and the TU Delft have recently announced their long-lasting partnership. Meanwhile, this cooperation has reached four key areas, one of which is aerodynamics. "The beauty of this project lies in the interdisciplinary nature of it," said Bregman. "Without all the knowledge from various disciplines, we would have never been able to execute it so well."