Design of 2017 WRC cars: CFD or wind tunnel?

The design of 2017 WRC cars was done in a relatively short period of time, as rules were initially approved during 2015, but were only fully fixed in July 2016. For most of the teams, designing, building and testing a new car, while at the same time competing in the WRC supposed a huge effort with different consequences: Citroen decided not to compete on 2016 championship, Ford took a lot of time to put the car on the road, while Toyota took advantage of not being involved in previous championships to get higher number of test days. VW and, to a lesser extent, Hyundai, were able to go ahead with their planning and were able to carry out a very extensive test programme.

But, what was the process they followed for the design of their aerodynamic package? Although some teams are very reluctant to give any information on that (Hyundai and understandably VW), some other have given some clues of how they did it.

Citroën followed the most common approach, by first designing the new car by numerical simulation, through the use of numerical codes, what is also known as CFD or Computational Fluid Dynamics, a work carried out by their own team. They did not start from zero, as they counted on the previous experience acquired with the Citroën C-Elysée WTCC. Also, they received support from Citroën design studio, in order to ensure rally car to resemble the production model.

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Scale model (40% of the real size) of Citroën C3 WRC for wind tunnel testing

C3 WRC design was then checked in the R.J.Mitchell wind tunnel of University of Southampton (part of UK National Wind Tunnel Facility), with a model 40% size of the real car. Results from wind tunnel were used to fine tune the CFD model and then to revalidate again as many times as required in the wind tunnel until modifications were approved. Only then were they tested, in the extensive test program Citroën carried out in 2016, which consisted of 9 major test sets.  All process was led by Laurent Fregosi, Technical Director, and C3 WRC project manager Alexis Avril.

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The vertical arm on top of the model is used to measure lift and downforce, in order to validate the effectiveness of the aerodynamic design.

A similar process was followed by Toyota, although no information has been released about their CFD work. While the design of the car was led by Simon Carrier, Toyota’s Chief Designer (ex-Subaru, ex-M Sport), CFD was most probably developed by the Computational Fluid Dynamics engineers of the Car Design and Development Department of the Toyota Motorsport R&D Center in Cologne, Germany. Chief Engineer Tom Fowler confirmed they tested in wind tunnel different set-ups, for gravel and asphalt, same as Citroen did. Although cars were fully prepared in Finland, and Toyota possess several wind tunnels in Cologne, the aerodynamic development was done in the wind tunnels of Mercedes AMG F1 Team, located in their facilities in Brackley, where they used scale models.

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Scale model of Toyota Auris WRC for wind tunnel testing

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A different approach was taken by M-Sport: due to time and money limitations, they did all design work of the new Fiesta WRC 2017 entirely by CFD, with no wind tunnel support or verification.  Chef Engineer Chris Williams counted on the support of an external company, Totalsim, which had previously collaborated with M-Sport in the aerodynamic development of the Bentley GT3, as well as with Prodrive in the design of the aerodynamic package of the Mini WRC that has been taking part in the WRC since 2011.

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It was not until March 2018 when, thanks to the support of Ford, the team had the chance to evaluate the car in the wind tunnel of Ford Performance, as we reviewed here.

Very little information was released by Hyundai or VW on their process design. It is believed that they have both continued to use their own resources, as in previous cars. For the initial version of the car back in 2013, the Hyundai i20 WRC was designed at Hyundai’s Namyang R&D Center in Korea, while it was being made race-ready at the Hyundai Motorsport headquarters in Alzenau, Germany. For the 2017 model process has probably been the same: the team Engineering Department led by Chief Designer Bertrand Vallat has been responsible of the full design of the new rally car (except for the engine) which means that they probably carried out their own CFD in Europe, while wind tunnel development was carried out in the Namyang R&D Center.

VW already developed the initial version of the Polo WRC back in 2012 with the aid of the VW’s Wolfsburg Design team and wind tunnel. For the 2017 model, the process was very similar, according to the explanation from François Xavier Demaison, VW Motorsport Technical Director. The design was developed by the team in close relationship with the VW Design Department, so every design in terms of aero had to be approved by Wolfsburg. People from Design and Marketing Departments were involved in any approval, as VW Polo is one of the top sellers of the German manufacturer and they had to ensure changes did have not an impact on future sells.

The results of the 2017 season do not show big differences between these two approaches, as Hyundai and Ford have been the leading teams in the fight for drivers and manufacturers titles, with no big differences in car performance.

This post includes the opinions of the author, which are certainly not always right. If you detect any error or you disagree, do not hesitate to contact us, by sending an email to wrcwings@gmail.com. We love to learn!

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