In preparation for Euro 7, Renault is scrutinizing the Master van in the wind tunnel. It will be some time before CFD fully aligns with wind tunnel results, but the new Renault Master serves as an exemplary aerodynamics success story. By Michael Gabriel, senior aerodynamic engineer, Renault utility vehicles department
Large utility vehicles significantly trail their passenger car counterparts when it comes to aerodynamic development. There are many reasons for this, including less stringent regulation, longer product cycles, poorly adapted resources and different customer priorities, but the winds of change have finally arrived.
Euro 6 regulations began pushing many larger vans into the category affected by the CAFE standards, and another significant step will be made with Euro 7 regulations set to take effect in 2027. Fierce competition is forcing OEMs to reduce their development cycles to stay competitive, while customers are being bombarded with information about the potential for operational cost reduction thanks to aerodynamically optimized vehicles.
Finally, with the December 2024 inauguration of the Automotive Test Section (ATS) at DNW’s Large Low-Speed Facility in the Netherlands, the large utility vehicle industry has a turnkey solution for precise aerodynamic measurement. In fact, the ATS is in complete accordance with the Worldwide Harmonized Light Commercial Vehicle Test Procedure requirements. This perfect storm of events will inevitably accelerate the shift toward more aerodynamically efficient utility vehicles.
When I was assigned as chief aerodynamic engineer on the new Renault Master project (XDD) in early 2018 – during the business strategy phase and just before the preconcept engineering kick-off – aerodynamic optimization for large vans was close to non-existent at the company. However, a competitor that had just won a coveted award was making a significant marketing effort to promote its world-class aerodynamic performance, which caught the attention of top management.
At the kick-off event a few weeks later, it was announced that the XDD Master would be the world’s most aerodynamic large van at launch. It was an incredible challenge. It took more than three years of focused teamwork to achieve the goal. Using a combination of competitor deep-dive analysis, hundreds of CFD calculations, around 200 hours of reduced-scale wind tunnel testing and regular intensive taskforce brainstorming, the general shape, engine cooling and exterior features were optimized. The achievement was confirmed during WLTP certification testing at DNW.
The result is a new Master large van family with 20% less drag and considerably reduced energy consumption. This means lower operating costs but also increased range and crosswind stability and, most importantly, without a negative impact on the vehicle’s utility, access, ergonomics or payload. The ‘advanced aerodynamics’ were specifically cited by the 25 international journalists that voted the new Renault Master IVOTY 2025.
While the XDD aero project can be considered a success at this point, the story continues with prep for Euro 7 certification. This month we will perform the first Master pre-Euro 7 certification testing using the wide-belt system for dual-wheeled utility vehicles. It’ll be a chance to test and perfect the Euro 7 aero package while also making our first use of the rolling resistance system in the ATS.
As I look back on my experience with this project, one subject particularly stands out: the issue of computer simulation versus physical testing. Clearly CFD will continue to gain importance and use as it is constantly improving. However, several large hurdles remain, which prevent an extremely accurate correlation with physical testing. The main limitation of CFD simulation is that it does not take into account model deformation.
At the 140km/h measurement speed of WLTP testing, things move a lot. Rubber air dams bend back, doors and hoods move outward, wheel arch liners and underbody panels vibrate, and the flexible air guides for engine cooling deform considerably. In addition, the tires and chassis change shape and position under the weight of the vehicle. None of this is taken into account by CFD, as the calculation burden would increase enormously.
In addition, utility vehicles have a huge wake compared with passenger vehicles, which accounts for a majority of the drag. A slight miscalculation in wake balance can have a large impact on the CdA result calculated by the software. Having compared a large number of wind tunnel tomography images and CFD wake calculations, I know that they are very similar but never identical. I believe a large part of the error in correlation I witnessed was caused by this discrepancy.
Therefore, I learned to use CFD for what it’s great at: visualizing the airflow. With CFD you can quickly detect early detachment at the rear, areas of localized turbulence and leaks in the air guides. There’s no better tool to explain to the architectural or design department why a change is needed. But when you need the precise drag value for a project milestone, or when it’s time to tweak the air dam or rear roof drop to balance the wake, you have to spend some time in the wind tunnel.
This thought leadership piece was published in the September edition of ATTI. Read the magazine online for free – it’s packed full of news, interviews and features, including how to maintain transparency in testing, the story behind the new Nissan Leaf, and the latest in battery testing and simulation