Get Firsthand Details With Aerodynamics From JLR’S Gaylard

One of the subject areas garnering the most attention at the SAE 2014 World Congress is aerodynamics because of its effect on vehicle efficiency through drag reduction and the potential of real-world fuel economy gains. Since just last year, the number of technical sessions linked to aerodynamics in the SAE World Congress has risen from seven to 10, and the quantity of technical papers on the subject has nearly doubled, according to Adrian Gaylard (Member, 2007), Activity Chair for Aerodynamics at the SAE 2014 World Congress and Technical Specialist-Aerodynamics & CFD at Jaguar Land Rover. SAE Magazines Assistant Editor Matthew Monaghan spoke with Gaylard prior to the World Congress to discuss the current state of the field and areas of further improvement.

Is the underbody the main area for aerodynamic improvement as automakers check out become more efficient?

There are things that you can enhance the underbody. Also the efficiency of cooling systems and vehicle cooling, generally. But there’s also still a lot of opportunity in the upper body. What tends to happen through the years is that styles change, and style language shifts, so you always have to go back and look at what opportunities that raises.

Is more attention being paid to aerodynamics with respect to cooling as a result of the move to more sophisticated powertrains?

Aerodynamic cooling flows have always been very important. Traditionally, you may have grilles and inlets in the front of the car, so it is able there to get drawn throughout the radiators or the heat exchangers, and that whole process generates drag. So there’s been an optimization exercise to ensure that you get enough cooling flow to your heat exchangers but not inducing a lot of extra drag. Automakers are starting to complete things like having grille shutters to make sure that cooling flow isn’t being taken into particular intakes when it’s not needed. EVs need cooling flowing different places for different reasons, so it’s been a long-term concern for automakers and may continue to be a thing that we look at very carefully, while we move into different powertrains.

Do you know the trends linked to aeroacoustic improvement? Are side mirrors considered the most important factor?

By no means the only contributor, even though side mirrors can be a big contributor. Road noise has decreased, and our products have become more refined, aeroacoustic sources that perhaps weren’t so intrusive in past times you can now hear them, as powertrains have gotten quieter. Door mirrors are important since they flow into the A-pillar as well as the vortex is generated. But additionally noise sources are generated over the windscreen, windscreen wipers, as well as underbody noise is generated through the airflow. Those all become important topics and important concerns.

What size of an impact does aerodynamics have on handling and stability?

It’s certainly influential. Speaking from experience with our own products, we’ve not had particular issues, yet it is something you must keep an eye on. Certainly as cars become lighter, then the aerodynamic impact of crosswinds and wakes of other vehicles becomes more important. Throughout the design process, you just have to keep close track of the side force and yawing moments your vehicles have to make sure that you retain those at acceptable limits. The trend for lightweighting means that we pay a bit more focus to that area in the future.

One of several papers you’re presenting in the World Congress is related to ground simulation. Which are the challenges connected with replicating that?

Certainly in Europe, moving-ground wind tunnels have become the brand new standard. It’s different in the U.S. I believe there’s just one current full-scale moving-ground wind tunnel from the U.S. (Windshear). There’s an increasing realization that in case we’re going to capture the aerodynamic resistance of a car traveling on the highway, then we have to have realistic boundary conditions, so the relative motion of the vehicle on the highway, and also wheel rotation, is important.

How would you see the mix between wind-tunnel, on-road testing, and CFD simulation for aerodynamic evaluation moving forward?

The total amount is shifting. At Jaguar Land Rover we’re relatively forward-looking, so CFD is our principal design tool for aerodynamics, which then we support with wind-tunnel testing. Traditionally, wind-tunnel testing is the lead technique, so what’s happened over the past 20 years is CFD has moved out of the research environment and into the development environment. That’s enabled us to work on our designs earlier as well as to exploit opportunities earlier in the process and do fewer late changes. I really do foresee a robust role for wind tunnels in the future, particularly advanced moving-ground wind tunnels-maybe tunnels that could start to simulate more of the real-world on-road environmental impacts. But certainly CFD is a more and bigger important part of everything we do.

Do you know the major challenges still to be overcome related to CFD for aerodynamics evaluation?

Probably the biggest challenge is the fact that all practical CFD simulation has to make up turbulence using some sort of general model. We can’t simulate it directly. There’s no general theory of turbulence; it’s one of the last unsolved problems in classical physics. So we’re always having to make some approximations ultimately to turbulence, and that does mean that there’s going to be some sort of difference with what we simulate from what we should measure. Also, to do a good job with aerodynamic simulation, you need to run large models that are very computationally hungry, so the challenge is having the entire speed of feedback that you want in your interactions with designers.

How does a gathering like the SAE World Congress help in your role for an aerodynamics specialist?

For me, it’s three days of immersing myself in a subject I love that I’ve been doing for the past 25 years. I have to see a number of what my colleagues are looking at in other parts of the industry, get to see some of the latest thinking from academia, and acquire to show several of my own work and have people ask me questions about it. So, we share knowledge; I do believe it’s really very valuable for that. Also, for the informal contacts you will be making and the network you increase of people with a similar interests, I believe it is very important.