Wind tunnels in the design and evolution of current WRC cars

In the first article of the series devoted to wind tunnels, we reviewed the role of these facilities in the history of WRC, from the 70s to 2016. It’s time now to review the role they have had on the current WRC car generation, from the initial design steps to the continuous development of the different evolutions of the cars.

DESIGN STAGE (2015-2016)

For the initial design of the 2017 WRC car generation, most of the manufacturers followed the classical design route: after the initial design is completed, the flow around the car and the forces it generates are modeled and numerically simulated through CFD software, usually commercial packages such as Ansys/Fluent or Star CCM+ or open-access software such as OpenFOAM. Once the numerical results are satisfying, a scale model is built for its evaluation and fine-tuning in the wind tunnel.

The use of scale models in the early stages of development presents multiple advantages: it is easier to work with (and to modify) scale models, and they can be prepared even before any full-scale model is available. Also, the number of scale facilities available is higher than the full-size, and they’re cheaper.

The evaluation of the Citroën C3 WRC was carried out at the R.J.Mitchell wind tunnel of the University of Southampton (integrated in the UK National Wind Tunnel Facility), with a 40% scale model. The R. J. Mitchell wind tunnel is a large and extensively equipped low-speed wind tunnel with a 3.5 m x 2.4 m (11’x 8’) working section and a maximum wind speed of 144 km/h (90 mph). Like all the other wind tunnels we will mention in this article, it is equipped with a moving ground, with the belt rolling at the same speed as air does inside the wind tunnel, to match the real conditions the car will face in a rally stage

Citroën C3 WRC scale model at the R.J.Mitchell wind tunnel of the University of Southampton, 2016 – picture extracted from the video Citroën C3 WRC – The Genesis, by Citroën Racing

Even at a small scale, the models contain as many details as possible, to allow optimal reproduction of the future car at full scale.

Another curiosity shown in this video shows is the study of alternative solutions for the C3 WRC, such as a small dive plane ahead of the rear wheels, similar to those of the Fiesta WRC. The video confirms they were considered but discarded.

For the initial aero evaluation of the Toyota Yaris WRC, Tommi Mäkinen’s team selected the Petronas AMG wind tunnel (max. wind speed of 173 km/h or 107 mph) of the Mercedes F1 team, located at Brackley, also with a 40% scale model. The models used included also all types of details, as well as solutions that were discarded after the tests, such as the extended plates exiting from the rear fender vents shown in the image below.

Toyota Yaris WRC scale model at the Petronas AMG wind tunnel of Mercedes F1 Team at Brackley, 2016 – extracted from the video Toyota Yaris WRC Backside story – development, by Toyota Motorsport Corp.

Once the design is refined with the scale model, the next step is the evaluation of the full-scale car at the wind tunnel. At this stage, bigger and more expensive facilities are required. Also, the number of adequate facilities is reduced, due to the requirements in size, power (required to reach airspeeds above 200 km/h) as well as additional elements such as a moving ground. This element is required for vehicles with low ground clearance, such as rally cars (in tarmac configuration), to minimize uncertainty during the assessment of their aerodynamic performance.

We found no evidence that Hyundai used scale models during the design of the Hyundai i20 Coupé WRC, but the full-scale car was evaluated at the Hyundai’s wind tunnel available at the Namyang R&D Center (max. wind speed 200 km/h or 124 mph). There are only a few images available from this facility, so we recommend you to visit it and to know a wind tunnel in detail, just by clicking on the great video below (by JP Performance).

Video of the Hyundai wind tunnel at Namyang R&D Center, by JP Performance

The initial development of the VW Polo WRC 2017 was carried out in 2015 at the wind tunnel available at Volkswagen facilities in Wolfsburg. However, due to the lack of moving ground, most of the tests were developed at the wind tunnel of the Research Institute for Automotive Systems and Vehicle Engines (FKFS) of the University of Stuttgart (max. wind speed 260 km/h or 162 mph).

M-Sport opted for the most radical design alternative: the aero package of the Ford Fiesta WRC was designed only with the support of numerical simulation (CFD) techniques. The reason why was the short time they had to complete the process, as the details of the new evolution of the Fiesta road car (on which it was based) only arrived in June 2016, just seven months before the first event of the 2017 season. Thus, they built the car only with the information obtained from the numerical results. Obviously, they tested it in real stage roads (like all the other teams) but still, they had skipped an important part of the design process. 

Even so, the design proved to be really efficient, as the car won the 2017 season opener event (Monte-Carlo) as well as the two World titles (Drivers and Manufacturers) that year.

S.Ogier/J.Ingrassia, Ford Fiesta WRC, Rallye Monte-Carlo 2017, 1st – picture by Tapio Lehtonen/Rallirinki

It was not until one year later when M-Sport finally developed the validation of the (CFD) numerical results in a wind tunnel. Thanks to the increased support from Ford Performance, one of the units of the Fiesta WRC aligned in Rally Mexico 2018 was sent to Concord, near Charlotte, NC (USA), to the Windshear wind tunnel (290 km/h or 180 mph). This facility, where Ford Nascar models are usually evaluated, allows the cars to be positioned at different slip angles, for optimal reproduction of the conditions that a rally car faces on a stage. There, under the supervision of Ford Performance aerodynamic engineers, the Fiesta WRC design was validated, as we reviewed in a previous post about this test.

Wind tunnel evaluation of the Ford Fiesta WRC in 2018 – video by Ford Motors Company

DEVELOPMENT STAGE (2017-2020)

Soon after the debut of the 2017 WRC car generation, the teams started to identify deficiencies and opportunities for improvement. The development of the 2017 WRC car generation process started then, and again, wind tunnels continued to play a very important role.

Once the car is competing, the wind tunnel evaluation is usually done with full-size models. allowing better reproduction of real conditions…but at a higher cost, and with the added problem of a reduced range of facilities available. The reason is that an optimal evaluation of a full-size car requires an optimized wind tunnel, with moving ground and variable slip angles, to assess aerodynamics during cornering, and there are not many facilities with all these features available.

Ford Fiesta WRC wind tunnel test, Windshear, Concord (NC), March 2018 – picture extracted from Ford Performance’s video

The Ford Fiesta WRC evaluation of the car made in the Windshear facilities had a second goal: to evaluate new modifications of the aero package of the car, such as the modified rear aero package that was introduced in the Fiesta WRC of Ogier/Ingrassia in Rally Finland 2018.

S.Ogier/J.Ingrassia, Ford Fiesta WRC, Rally Finland 2018, 5th – picture by Henri Vuorinen Photography

Toyota has also validated in the wind tunnel most of the modifications implemented in the car. This is the case of the new front aero package of the Yaris WRC, which was validated at the wind tunnel of Toyota Motorsport GmbH in Köln, Germany (max. wind speed of 252 km/h or 157 mph), with a full-size car, in August 2018. The validation was done several months after the introduction of the new aero package in the car, which took place in January 2018 in Rallye Monte-Carlo.

Toyota Yaris WRC full-size model at the Toyota Motorsport GmbH wind tunnel, Köln, 2018 – picture extracted from this video by Toyota

The latest aero modifications homologated for the Yaris WRC were again evaluated at the Mercedes F1 Petronas AMG wind tunnel, with a scale model, as shown in this video by Mercedes and in the pictures below.

Toyota Yaris WRC scale model at the Petronas AMG wind tunnel of Mercedes F1 Team at Brackley, 2019

The pictures show the scale model used in 2019 to evaluate the new design of the rear wing, which was homologated in September 2019 and introduced in Rally Turkey that year.

Hyundai i20 Coupé WRC wind tunnel test at Pininfarina facilities – extracted from Hyundai Motorsport’s video

Also, Hyundai has validated the complete redesign of the latest aero package of the i20 Coupé WRC in a wind tunnel in 2020. Surprisingly, not only at Namyang facilities but at the historical wind tunnel of Pininfarina (250 km/h or 155 mph), also with a full-size car.

Hyundai i20 Coupé WRC wind tunnel test at Pininfarina facilities – extracted from Hyundai Motorsport’s video

In short, the role of wind tunnels in the design and development of WRC cars remains as important as it has been in the past. So they must be very busy at the moment working on the design of the new generation of WRC cars for 2022.

If you’re interested in learning how a wind tunnel works, we recommend you to watch these great videos:

 

 

 

 

 

6 thoughts on “Wind tunnels in the design and evolution of current WRC cars

  • 2020-12-30 at 09:07
    Permalink

    Congratulations on your work. I would like to receive your future updates. thanks

    Reply
    • 2020-12-30 at 09:26
      Permalink

      Thank you Andrea, we’re happy that you enjoy it. You can subscribe to the blog just by entering your email address in the subscription form you can find in the left column of the blog, and you will receive a notification in your email every time we post an article. Or you can follow us through social media (twitter account @llluis555 or facebook).
      Happy new year!
      Lluis

      Reply
  • 2021-01-02 at 03:22
    Permalink

    Merry Christmas and Happy New Year! Haven’t been able to read this article owing to regular holiday business, so here I am! A few questions as usual, if you don’t mind:

    1. Are the teams limited in wind tunnel usage (scale model size, runtime, etc.) and CAD analysis like most high-level championships? It’s especially strict in F1 & MotoGP, but relatively free in WEC & global touring car.
    2. Are the run plans in the wind tunnel affected by the size of the model? What I’m specifically implying is comparing how easy/hard it is to test a 40% vs. full-scale models.
    3. How do teams simulate extreme gravel and snow rallies in the wind tunnel? Or can they even do that? I’m talking about the rapid suspension and platform movement experienced in these rallies changing the aero surfaces angle of attack.
    4. Do the tyre supplier give teams wind tunnel tyres, or are they forced to run metal tins like in the old days?
    5. A non-wind tunnel question: Which car do you think is currently the best? Toyota or Hyundai? It’s difficult to discount the drivers’ performance in these cars because of the nature of rallying, so I hope I can have your opinion.

    Wishing you a great 2021!

    Reply
    • 2021-01-03 at 09:58
      Permalink

      Happy new year Kevin! Your questions are more than welcome.
      1. AFAIK no, there is no restriction. I guess the limitation in joker availability makes the job, while in other Championships they are allowed to make changes race after race.
      2. Results from a scale model are not always applicable to full scale, quantitatively. But still, you can draw very good conclusions qualitatively. To get the full translation from scale to real size, you should keep the same Reynolds number. This means that reduced size should be compensated with higher speed (which is almost impossible) or higher fluid density (using water would help, and some people do, but it is not very common).
      3. The only thing they can do (as you can see in this video by Mercedes, it is to raise and lower the car, to study the effect of different car heights. Or to change the angle of attack of the air, like this video by Ford Performance shows.
      4. At full scale, they used normal tires. At a smaller scale, pictures show both (metal wheels in the Toyota or normal tires in the Citroën.
      5. That’s the most difficult question. My guess is that they are currently at a very similar level, no matter who is driving them. Just look at the stage results (although we have had very few this year) and you’ll see both cars are fast no matter the nature of the stage or the driver. Maybe, with the new modifications we have already seen for the next season, we can see more differences, but personally, I doubt it, as they all go in the same direction (better front grip) and they both seem effective to me. We will see, hope we can have a normal season from springtime.
      Thank you, Kevin, happy and aero 2021!

      Reply
  • 2021-01-03 at 16:56
    Permalink

    Hello ! Finally found a page that goes deeply into rally cars aerodynamics !
    Got some questions !

    1. How much do you think aero is going to change in the new upcoming generation (2022), as it will be changed to a more simple spec. ?

    2. Do (and if yes, then how radically) the car chassis impact the car’s airflow/aero design and the development ? The Yaris for example is basically smaller in any dimension than the i20. Does it give Toyota an advantage to design more aggressive aero and not worrying that much about the drag ?

    3. Maybe I am wrong but I think I have heard, that Toyota designs their 2022 car’s chassis from scratch. The shape of it is basically the same, but not taken from the road-going Yaris. If it is true then if and how big advantage it would aero-wisely be ?

    Reply
    • 2021-01-03 at 17:53
      Permalink

      Hi Laur! Happy that you found us, and we hope you like it!
      1. It’s difficult to say, as FIA, as usual, gives poor information about the new regulations. I would expect a reduction of around 25% of the current downforce…but it’s just my guess.
      2. The chassis is crucial for car handling, but aero wise it is only relatively important. Of course, the smaller the front area, the better (for the drag), while the car length has little effect on the aero, and the ride height can be regulated independently of the chassis. Even in the case of the Yaris, the drag is important, but the whole aero design is made to generate more and more downforce, with the minimal drag cost. Another thing is air cooling: there, a good chassis can help a lot. Also, in terms of rigidity, the more stable, the better for the aerodynamics.
      3. Yes, because in 2022 cars tubular chassis are allowed. Again, better for cooling and rigidity, while in terms of aero, the advantage is small.
      Thanks!
      Lluis

      Reply

Leave a Reply

Your email address will not be published. Required fields are marked *