All-New Wind Tunnel Lets Honda Air It Out
Honda’s aerodynamic and NVH development gets a breath of fresh air from its first full-scale wind tunnel in North America.
Acknowledging the twin priorities of aerodynamic and NVH optimization in the increasingly electrified passenger-vehicle future, Honda in late March inaugurated its first full-scale wind tunnel in North America. The $124-million Honda Automotive Laboratories of Ohio (HALSO) facility, built on the grounds of Ohio’s sprawling Transportation Research Center is conveniently adjacent to Honda’s longstanding product-development and manufacturing hub that spans the East Liberty and Marysville areas.
“Conveniently located,” isn’t the half of it. Prior to the opening of the HALO wind tunnel – which currently is running a single shift but will be “fully operational” by Fall 2022 – Honda’s U.S. operations rented wind-tunnel time in a variety of locations because the company’s only full-scale tunnels are in Japan and Europe. Shipping prototype vehicles and accompanying engineers and technicians to rented tunnels is an enormous direct cost, said Mike Unger, lead manager for the new facility. But maybe worse is the detrimental impact on ever-tightening vehicle-development timelines. It all can be a huge hassle, leading Honda some years ago to begin planning HALO’s wind tunnel in Ohio.
It is “the world’s most-advanced wind tunnel,” Unger flatly claimed during a media walkthrough of the 110,000-sq.ft. (33,528-sq.m) facility that houses the one-eighth-mile tunnel itself as well as a variety of no-prying-eyes “customer” workbays to serve the third-party entities envisioned to lease the facility as Honda reverses the renter-landlord relationship. Then again, Unger concedes, given the relative global scarcity of full-scale automotive wind tunnels, just about every totally new tunnel becomes the de facto world’s best.
In the roughly two-year project, the designer and general contractor for HALO’s wind tunnel was Dallas, Texas-based Jacobs Technology. The College of Engineering at Ohio State University reported last year that as Honda was evaluating the wind tunnel project, company personnel visited Pininfarina in Italy and met Antonello Bianco, a wind-tunnel expert and currently senior researcher at Ohio State’s Center for Automotive Research, who also advised Honda on the project.
A central feature of Honda’s new wind tunnel is the novel “modular” moving ground plane (“rolling road”) system that allows for quick, four-hour changes between the five-belt rolling-road dynamometer and a wide-belt rolling road. The belts, used to mimic the action of the vehicle in motion, are sheets of stainless-steel composite less than 1mm thick.
Vehicles that are more or less conventional (i.e. crossovers, SUVs and other vehicles with everyday ground clearance) are tested on the five-belt module, one at each wheel and a wider belt running down the underbody of the vehicle. Special vents assure the flowing air isn’t collecting in unwanted areas, particularly in front of the moving wheels. And to also ensure the least amount of rolling resistance, the vehicle’s axles are disconnected and brake pads are removed.
For low-riding racecars and sportscars, the wide-belt ground plane – which can run at up to 193 mph (311 km/h) is more desirable because of the crucial nature of the air boundary layer at the front of the car. This is where the modular system – supplied by Minnesota’s MTS – comes into play. A crane positioned outside the testing area slides over to remove the rolling road as a self-contained, 40-ton cassette. Then the desired ground-plane dyno is inserted into its place. Although the four-hour time to swap between rolling-road modules is a boon, Unger concedes ideal test planning wouldn’t rely on such hot swaps. Vehicles, meanwhile, can be changed in 60 minutes or less, Unger claimed.
Atop each rolling-road module is a 12-m. (39.4-foot) turntable to which the vehicle is secured. The turntable can be rotated to any position up to 180 degrees relative to the airflow. Underneath is an ultra-precise three-axis balance system that serves several purposes, one of the most important being to measure aerodynamic drag force. Honda said its sensitivity is plus-or-minus about 2.5 Newtons, or the weight of a D-size battery. The entire setup can assess some 2700 channels measuring load, force and balance.
To ascertain precise readings of general noise, flutter, frequency and other wind-generated effects, the new wind tunnel is designed to quickly and easily enable the setup of comprehensive acoustic arrays supplied by Siemens. The top, front, side and interior arrays can deploy up to 502 external microphones (as well as cameras) and 54 in-cabin microphones.
When the test chamber is set up for aeroacoustic NVH measurements, a special acoustic cover is placed on the turntable because the rolling road is not required when the only concern is the noise and other effects created by the wind. The chamber itself is painstakingly sound-deadened: at a wind force of 87 mph, there is just 56.5 dBA of ambient noise, helping the microphones to pick up the most subtle of noises from airflow over the vehicle.
The wind-related NVH metrics don’t stop with the microphone arrays. Interior noise testing also can encompass the use of the distinctive “Aachen head” test dummies, which can perceive and record noise in the same fashion it would affect a human occupant.
Gale force – and then some
The wind tunnel’s test chamber is set up as a “variable-nozzle” layout in that if the widest configuration of 25 sq. m (269 sq-ft) is used, the maximum air velocity equates to 155 mph (250 km/h). The tighter 18 sq-m (194 sq-ft) setup can deliver the tunnel’s maximum 192 mph (310 km/h) wind speed. The airflow is generated by a GE-made fan that’s 8m (26.3 ft) in diameter and is propelled by a 5-mW, 6700-hp electric motor. The fan requires just 250 rpm to generate the facility’s 192-mph maximum wind speed.
The wind tunnel’s fan sits aft of the test chamber in terms of the airflow circuit. Just downstream of the fan is a 2-story-high wall that forms a hulking heat exchanger to deliver air to the test chamber at precisely the required temperate. The heat-exchanger wall circulates 16,000 gallons of propylene glycol to deliver constant air temperatures ranging from 50 deg. F (10 deg. C) to 122 deg. F (50 deg. C). Any temperature in that range can be achieved in a maximum of 30 minutes.
Unger conceded that the industry’s newest wind tunnel typically is judged “the best” given the roughly decade or more between new tunnel constructions. Some existing wind tunnels may be marginally better at some practice or another than Honda’s new facility, he allowed, but “In terms of breadth of capability, this tunnel is unmatched,” he said.