'As fast as a hurricane': I went inside General Motors's massive wind tunnel

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Despite having the technical capability to go all virtual, the full-scale wind tunnel at General Motors's Tech Centre is busier now in 2024 than it has ever been.

Electrified powertrains have placed a greater emphasis on ensuring a car is as aerodynamic as possible, in order to go as far as possible, while remaining quiet to all extraneous noise.  

It wasn't until the 1970s that car makers started to get serious about automotive aerodynamics, but the science behind making a car as efficient as possible continues to break new ground, even today.

General Motors’s underground facility in Detroit, United States was opened in 1980 and remains one of the largest automotive wind tunnels in the world. It was last upgraded in 2016, adding a rolling road to mimic the aerodynamic effect of tarmac underneath a car's floor pan.

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Especially in the age of electric vehicles, where aerodynamics and driving range are of utmost importance, GM's vast wind tunnel facility runs 24/7 just to keep pace with testing demands.

Drive was given a special opportunity to tour GM's wind tunnel during a recent trip to the United States to test the new Cadillac Lyriq, a large-sized electric SUV that's destined Down Under before the end of 2024.

The tunnel is arranged in a circuit rather than a single linear tunnel and measures roughly 320m long in total. The facility is made entirely of concrete that’s up to 45cm thick in certain sections to minimise vibrations and noise infiltration.

Within the test area itself, the test subject sits on a turntable to allow engineers to test aerodynamic effectiveness in the event of a crosswind. There’s a sharp ramp-up design immediately before the test area that forces large amounts of air through a tighter opening – this allows GM to achieve higher wind speeds for validation purposes.

The facility is busy enough that GM doesn’t rent it out to other car companies, but it is occasionally used for outside purposes. GM is a sponsor of the Canadian national downhill ski team, which has used the tunnel to test its athletes in years past.

Speaking to GM's wind tunnel engineers about the constant activity the tunnel sees, the styling of a car can be a constant push-pull discussion between designers and engineers.

It's a struggle that Joel Ruschman, GM's lead aerodynamicist for electric vehicle platforms, is all too familiar with.

"It’s constant back and forth with our [design] studio partners – and they really are partners," Ruschman tells Drive.

"Aerodynamics doesn’t sell cars. Styling sells cars. But we also want to make sure that we’re delivering the range to our customers [that they expect from an electric vehicle].

"We don’t want to be delivering a vehicle that gets terrible range, looks awesome, but gets terrible range.

"So we do work very, very tightly with our studio counterparts and try to resolve all of those issues."

A major breakthrough for aerodynamic studies concerns the introduction of computational fluid dynamics (CFD) technology, which allows engineers to virtually design a car using computer software and then test the airflow around a car.

This means subtle changes can be made to a car's design that can be tested almost immediately, rather than waiting for designers to physically alter a clay model or to design new panels for a car.

"We’ve since moved away from clay vehicle development. We’ve pretty much gone more towards a virtual development because it allows us to be very agile, very quick with our changes," says Ruschman.

"With the clay vehicle, we are limited in terms of hard parts, we have to install parts onto the vehicle, but in the computer we can make swaps as soon as the design changes and have results days later instead of sometimes weeks later for a clay vehicle."

Final aerodynamic tests and sign-off are still completed using the wind tunnel due to regulations, and to effectively test wind noise, but CFD has removed time and money constraints from the test phase and now allows designers to push cars through the design phase faster.

Ruschman says minute changes in a car's exterior design can often add up to a much larger result.

"Electric vehicles are very sensitive to aerodynamics," he says.

"Except for the powertrain itself – the motor and the batteries – aerodynamics is going to be the number-one driver of range, especially when you’re driving on the highway.

"Effectively a one per cent improvement in aerodynamics… equates to about a one-kilometre range improvement.

"But what does a one per cent improvement in aerodynamics actually look like? It’s very, very small changes,” he continues.

"So, if you have a sharp edge in the front of the car and you just put a [curved] radius [instead], a little bit of a radius will give you one kilometre of range. So, imagine you’re making changes like that all over the car."

You'll see manufacturers introduce new ways to solve old problems, such as the introduction of side-view cameras in place of large mirror housings.

According to Ruschman, anything designers can do to reduce the size of the vehicle or to remove appendages will smooth the overall air flow around the vehicle.

However, he maintains that pop-out door handles have minimal aerodynamic benefit over conventional pull handles.

"I definitely have seen a lot of the industry moving away from this, or sorry, moving away from the traditional door handles and [towards] the flush mount," says Ruschman.

"But I think it is just mostly because customers really want that delightful cool [design] aspect.

"I love them just because it's an aesthetic thing. But as far as aerodynamics goes, it’s actually not as much of an impact as you would think."

But it can help reduce wind noise, a discipline that's become a key focus for electric vehicle development.

“So EVs don’t have engine noise, but they do have a lot of road noise," says Ruschman.

"They’ve got wind noise, and so you’re able to hear that a lot more prevalent in the car. So we spend a lot of time tweaking small details in the mirrors, radii all around the vehicle, and how the parts attach to each other’s seals.

"Because what we want to try and do is make sure that when you’re driving your very quiet EV around, you don’t hear an annoying little whistle that’s just coming from somewhere in the vehicle."

GM's wind tunnel is purpose-built to mimic the exact environments cars will face when out in the real world – whether it's in terms of aerodynamics or wind noise.

In a perfect world, GM's CFD analysis accurately represents what engineers will find in the wind tunnel, which in turn mimics real-world aerodynamics.

Effectively, GM engineers have been able to ensure there is no delta between the three disciplines.

The entire laboratory is separated into three parts: the offices and monitoring stations, the closed-loop tunnel, and the test section.

The test section has seen the most development over the decades, including being lined with acoustic foam to reduce background noise levels and the installation of a rolling road underneath the vehicle.

Comparatively, the closed-loop tunnel has seen little change. Instead of being a simple tunnel, the design of GM's facility incorporates a concrete circuit that channels the air through four chambers using gigantic turning vanes.

Walking through the entire tunnel circuit, it's eerie how quiet the test chamber is compared to the closed-loop tunnel. You can almost hear yourself think when you're standing beside a test subject in the chamber, while the relative echo experienced in the wind tunnel seemingly reverberates forever.

If you've ever stood in an empty concrete chamber, you would have noticed the material is stubbornly echoic.

The sheer size of the closed-loop tunnel is astonishing, especially given the relative size of the test section where cars are placed.

The fan itself is roughly 13m in diameter and is constructed using Canadian Sitka spruce wood, known for its strength and resistance to damage.

Even after more than 40 years, the original fan blades are still in use with only minor repairs required. They can spin at up to 270rpm, which allows for a maximum wind speed of 210km/h – as fast as a category-four hurricane.

However, testing regularly occurs around the 110km/h wind speed mark, roughly equivalent to freeway speeds around the world.

It’s incredible how a facility built more than 40 years ago continues to be able to accurately pinpoint real-world implications.

Joel Ruschman notes that the drag coefficient value as tested in GM’s wind tunnel is identical to the value recorded using virtual testing, which is identical to real-world experiences once the car is out and about on public roads.

In a world of continuous innovation, the wind tunnel persists as one seriously impressive – and accurate – tool of automotive design.

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