Sorting the Wheat from the Chaff

Computational fluid dynamics (CFD) helps to design better off-highway vehicles.

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by Ashkan Davoo and Titus Sgro of Siemens PLM Software

Designers of commercial vehicles are under ever-increasing pressure to cut program development times and costs, while at the same time meeting increasingly rigorous demands of reduced emission and fuel consumption regulations.

For the Off-Highway sector, those challenges are further compounded by the need to develop platforms that are versatile and robust enough to perform well across the many variants that will be spawned from a single-base vehicle, some of which will inevitably be required to operate in challenging environments with regard to temperature extremes, terrain and dirt management. Finally, but most importantly of all, vehicle designers must provide a safe, quiet and comfortable working environment for vehicle operators. Increasingly, Off-Highway OEMs are meeting these demands with the help of extensive engineering simulation, which assists them to predict the performance of their vehicles from early in the design process by constructing detailed virtual prototypes of the entire vehicle.

CNH Industrial is a global leader in the capital goods sector that — through its various businesses — designs, produces and sells a wide variety of vehicles, ranging from agricultural and construction equipment to commercial vehicles. The company also supports a broad portfolio of powertrain applications. From tractors and combines, excavators, wheel loaders, trucks, buses, firefighting and civil protection vehicles to powertrain solutions for on and off road and marine, the group sells, “machines for work.”

Across its 12 brands, 62 manufacturing plants, 48 research and development centers, and with a workforce of more than 71,000 people, CNH Industrial is present in 190 countries worldwide giving it a unique competitive position.

In order to understand how CFD has affected vehicle development in the off-highway sector, Ashkan Davoo and Titus Sgro of Siemens PLM Software spoke to Luc Dupon and Pieterjan Platteeuw, who are responsible for design analysis and simulation at CNH Industrial in the Zedelgem engineering team.

“We cannot imagine a world without CFD here in product development. There is no way back.”

Having worked for the company for over 30 years, Dupon has witnessed the growth of CFD in the commercial vehicle industry first-hand, starting off over 10 years ago as a mere curiosity, to today where it plays a central role in vehicle development programs.

“In the past few years, CFD has become very important to us, especially in helping us to design products that meet and exceed the requirements on new emissions regulations,” Dupon says. “Before the arrival of CFD, we had no choice but to rely on experimental testing, and a process of trial and error. Our success in those days relied heavily on the experience of our engineering team, with product development driven as much by engineering intuition as hard data.

“Although this process delivered some excellent products, the cost of making a wrong design decision that would only be exposed by testing late in the cycle was very high. CFD allows us to mediate that risk through building virtual prototypes early in the design process.”

However, before CFD could be considered as a serious alternative to physical testing, it first had to overcome some credibility issues. “When we started using CFD (over) a decade ago, people were not confident in its capabilities or in the accuracy of its results. They would tell us, ‘We can do this faster in experiment than you can do in your simulation,’ ‘You have to estimate your parameters,’ or even ‘You don’t know what you are doing,’” Dupon says, before adding, “No doubt, in the very early days, they were often right. However, by consistently delivering high quality results that correlated well with experiments, we managed to gradually challenge that perception. Today, the mood is rather different, and there is real belief in the power of engineering simulation.”

Despite this obvious success, both Dupon and Platteeuw are anxious to point out that CFD has not replaced physical testing in the off-highway product development process.

“CFD and experimental testing are complementary tools, they work best when used together. At CNH Industrial, we continue to correlate our CFD models against data from physical tests to make sure that we can continue to be confident in our future simulation results. I firmly believe that testing and CFD will always go together,” Dupon says.

Adds Platteeuw, “You have to see how the product performs out in the field. In our case, that literally means ‘standing in the field,’ as we have to understand the role that weather, terrain and crop type have on our CFD models. In order to properly simulate the physics, we have to understand all the boundary conditions, especially as the demands of the commercial vehicle industry constantly drive us to using bigger, more complex models that more accurately capture all the relevant physics.”

In just over 10 years, CFD simulation has evolved from being an “interesting curiosity” to occupying a central role in the commercial vehicle development process.

“We cannot imagine a world without CFD here in product development. There is no way back,” Dupon says.

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