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The wind tunnel perfects the art of silent electric cars

The wind tunnel perfects the art of silent electric cars

You’d expect a carmaker of Honda’s reputation to have all the latest car development tools—including new battery-electric vehicles (BEVs)—at their fingertips. But for years, the Tokyo-based automaker has been renting wind tunnels from other auto and aerospace companies and governments around the world to bolster its own facilities. That will change this fall when Honda finishes calibrating its state-of-the-art $124 million wind tunnel in East Liberty, Ohio, and begins aerodynamic testing.

The new Honda Automotive Laboratories of Ohio (HALO) factory will do more than just help road and race cars be aerodynamically smooth and fuel efficient; it will also allow Honda to fine-tune the sound of the air flowing over those vehicles. Wind noise is noticeable in any car, but in a battery powered electric vehicle it is a major distraction. A wind tunnel that can help designers keep noise to a minimum could be a boon to the electric vehicle (EV) industry.

It is reasonable to associate wind tunnels with airplanes, as aviation advanced pioneering work in aerodynamics. However, wind tunnels have also been a part of the automotive industry since 1960, when the first purpose-built automotive wind tunnel – the Research association for the motorcycle industry tunnel – became operational at a former Royal Air Force airfield in Warwickshire, England. To provide airflow, it used four aircraft propellers as fans, each powered by a 325 horsepower electric motor.

In the decades that followed, automotive wind tunnels spread worldwide, including a trio of Honda tunnels in Japan. While Honda’s wind tunnels have served well, they have failed to meet the company’s vehicle development demand, particularly in its largest market, the United States.

“We had rented [wind tunnel] facilities around the world for the longest time,” said Mike Unger, full-scale wind tunnel leader at Honda R&D Americas. Popular mechanics† “It costs a lot of money to ship quite expensive prototype cars around the world.”

That strategy also puts such one-off prototype cars at risk, as evidenced by the sinking of the roll-on roll-off car carrier Felicity Ace in March, when thousands of luxury vehicles – including Porsches and Lamborghinis – went down with the ship after it caught fire in the Atlantic Ocean. Not to mention Honda’s other thorn in the side: the cost of the engineers constantly traveling (sometimes as many as two weeks a month) to rented wind tunnels all over the map.

“It got to the point where our development load got high enough that [leasing] made no sense anymore. In the end, we came to the conclusion that ‘Hey, we need to build our own wind tunnel,’” says Unger.

The sound of drag

The wide belt module is used to test the aerodynamic performance of vehicles with a low ride height, such as sports cars and racing cars.

Honda

Discussions about a new tunnel began in 2015, when Honda envisioned a facility that could measure all of the things automotive engineers and designers care about most, from a vehicle’s overall drag coefficient (a measure of an object’s drag in a liquid environment such as air or water) to the way the air flowing over it sounds to the driver and passengers.

The auto industry “only builds one of these tunnels every 10 years,” Unger explains, so getting the most out of it is vital. That includes integrating aeroacoustics – the ability to measure the sound around a car – for a very important reason.

“With BEVs, there is no engine and no exhaust, so wind noise becomes much more noticeable,” Unger says. (While BEVs are EVs, not all EVs are BEVs; battery-powered electric vehicles store electricity from an outside source in a battery, while electric vehicles can receive electricity from stored on-board hydrogen, a combustion generator, or even solar panels.)

Minimizing wind noise for electric vehicles is a new facet of the noise vibration and hardness (NVH) factor that automakers have been trying to tune and reduce for decades. It’s also something that manufacturers can eventually promote in their marketing. Honda’s new tunnel includes a system of acoustic arrays, consisting of microphones and cameras, capable of accurately measuring sound in real time. The silence of the tunnel itself actually enhances the sensitivity of the arrays.

“If you’re in the state [tunnel] test section, the wind noise at 87 mph is less than 57 [decibels]”, Unger announces.

According to Yale University’s decibel level comparison chart, which is similar to the hum of a household refrigerator. Despite the wind generated by a huge 26-foot-diameter main fan powered by a 6,700 horsepower (5 megawatts) electric motor, the silence inside allows for a more accurate sonic reading of cars or other objects placed within them. Power will come courtesy of Honda’s Transportation Research Center (TRC), which surrounds the new facility.

Aero for everything from Econo boxes to Halo Cars

honda wind tunnel

The HALO wind tunnel will be part of Honda Performance Development’s development tools, from top IndyCar and IMSA Sports Cars races to commercial racing programs.

Honda

“This tunnel is hard to beat in the world,” Unger says. The aerodynamic and sonic tuning capabilities apply to everything from Honda’s most modestly priced Civic LX to his $170,000 NSX supercar, the kind of flashy, powerful ride commonly referred to as a “HALO car.”

HALO broke ground in 2017 and construction of the 110,000-square-foot facility was completed last year. The 10-by-16-by-49-foot open test section of the tunnel includes a 39-foot diameter turntable that can turn a car 180 degrees relative to the relative wind. (Most wind tunnels only turn plus or minus 15 degrees.) There are two nozzles available for varying speeds: an 82 square foot nozzle, which can generate airflow up to 250 mph, and a smaller 59 square foot nozzle, which is capable of to 192 mph current.

The ability to blow air at nearly 200 mph means HALO will also be useful for racing car development and testing. Honda has already had its wind tunnel correlation IndyCar in the facility. (Honda engines power about half of the IndyCar teams.) Whether the HALO aerodynamicists need to measure cars at race or highway speeds, they can rely on two 40-ton rolling road tire modules (a single wide tire and a five-band road). ) to locate the aerodynamic interaction of fenders or open wheels with the surface.

Each treadmill module is essentially a giant treadmill powered by an electric motor. The treadmill sits on a calibrated balance with a three-axis load cell, allowing engineers to measure all the forces on the test car sitting on top of the rolling road. The belts ride on pulleys with intricate cooling, tracking and vacuum systems to ensure they stay cool at speed, and they run straight and flat like a road. The “incredibly durable and specialized” belt material is smooth, Unger explains, and provides just enough friction to keep a car’s wheels and tires spinning.

Honda engineers can swap the modules under the turntable, a process that takes about four hours. The wide tire road, which can run up to 193 mph, is used for race cars and high-performance cars. Two struts, attached to the front wheel hubs, secure the car.

“Especially for open wheel cars, spinning wheels are vital to get the right one [aero forces] answer,” explains Unger. “If the wheels aren’t turning, you’re leaving out a lot of the aerodynamic signature.”

Wheel rotation is less important for cars with mudguards or SUVs with higher ride heights. To assess the aerodynamics of the bodywork of such vehicles, Honda uses the five-band road capable of up to 155 mph. (One strap is located under each vehicle tire and one larger strap is located under the center of the vehicle.) The module has four posts, which clamp the pinch weld line of the car chassis between the front and rear wheels.

Accuracy and fresh air

honda wind tunnel

The acoustic test system consists of a series of acoustic arrays – top, front, side and interior – with 502 external microphones, 54 internal microphones and cameras to locate sound sources.

Honda

Accuracy is paramount to any wind tunnel, and Unger says HALO pushes the resolution of modern tunnels. It can take aerodynamic pressure of up to 2.5 Newtons (about the weight of a standard D battery). And with power-limited EVs, that precision is even more important.

“Aero is going to be the driving factor in the range,” Unger notes. “We strive to squeeze every possible resistance out of the design.” In general, a 10 percent reduction in a car’s drag is equivalent to an increase of about 0.5 mpg. Such large reductions in resistance are made when a new model is designed or redesigned. HALO will be used later in the design phase to adjust resistance, squeezing out improvements of 1-3 percent. Combining minor improvements with brakes, bearings and other lower rolling resistance components, a 2022 Accord can go an extra mile or so within range.

“If you work with a machine for as long as we do, it develops a personality. When a certain sound changes, people who have been there for a long time immediately know that something is going on.”

But what works in the wind tunnel or the digital world may not always work in the real world. So Honda has three “correlation cars” – cars that have been tested on the road and in other wind tunnels – with known aerodynamic characteristics that it can use to confirm the data that HALO generates.

The sensitivity and capability of HALO is impressive, but so are the conveniences for the engineers who will be working there. Thanks to the wide access, cars can be loaded and unloaded quickly. Movable arrays make switching from acoustic to aero mode a half-hour breeze. The versatile quality allows engineers from different disciplines from different countries to work side by side, both from and learning from each other. The adjacent control room also has a break room and outdoor patio, which Honda’s wind tunnel leader says is anything but superfluous.

“You can get some fresh air and see the sun instead of staying in a cave for 12 hours at a time. I’ve tested enough over the years that I can remember going to work after dark and leaving when it was dark. Do that for a month at a time, and things get pretty dark in your world.”

The tunnel’s novelty means it has yet to be given a nickname or fully reveal its windswept nature to those who will be working day in and day out. But Mike Unger assures me that HALO will show up sooner or later.

“If you work with a machine for as long as we do, it develops a personality. When a certain sound changes, people who have been there for a long time immediately know that something is up. It could be a tone change or a little vibration and we know it. We are still figuring out what the personality of HALO will be.”

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