The Massachusetts Institute of Technology (MIT) has recently unveiled its new, state-of-the-art wind tunnel replacing its 80-year-old predecessor. Now the most advanced wind tunnel in the United States, MIT has high hopes for the tunnel in the future.
Back in 2017, the MIT Department of Aeronautics and Astronautics (AeroAstro) announced it would replace the tunnel with a brand-new facility thanks to a lead funding commitment from Boeing. The new tunnel can reach wind speeds up to 230 miles per hour (370 kph) and has the largest test section in U.S. academia.
This is a much-needed upgrade for the institute, as the older tunnel was aging quite poorly.
“If I had one word to describe the state of the old tunnel after 80 years, it would be decrepit. The tunnel shell and supporting foundations, the instrumentation, and the drive motor and fan were all in a state of decay. The airflow quality was poor, and the tunnel was extremely loud and power-inefficient,” explains Mark Drela, the Terry J. Kohler Professor and director of the Wright Brothers Wind Tunnel.
“It just wasn't holding up against our modern standards of wind tunnel testing. Our goal was to bring our vintage tunnel into the 21st century and beyond, and we did that.”
What are wind tunnels used for?
Wind tunnels have been around for over 150 years, with the likes of Wilbur and Orville Wright using one before their historic flight in 1903. They tested candidate wing designs in their self-built, simple open-ended wind tunnel.
Since almost everything on the Earth's surface is surrounded by air, wind tunnels are great tools to circulate air over a stationary object in a controlled setting, allowing the operator to obtain aerodynamic data instead of moving an object through the air. When designing something that interacts with airflow, it's critical to understand and forecast the aerodynamic forces at work in order to diagnose and correct any flaws in the design.
Wind tunnel measurements can be used to estimate how much fuel an aircraft will spend, how slowly it can land, and how long it will take to take off. They can also monitor wind loads on stationary objects like bridges and buildings, as well as aerodynamic loads on ground vehicles like cars and bicycles.
Wind tunnels are also used by scientists and engineers for basic research, such as investigating how air behaves when it interacts with an item to better understand fluid mechanics.
Most modern wind tunnels aim to provide as "clean" airflow as possible over a model, and this tends to require as large a wind tunnel cross-section as possible. For the new tunnel, this would take some serious redesigning, however.
“Like any engineering project, size and cost were major considerations. We couldn’t just take the design of a conventional tunnel and size it to fit into the old tunnel’s relatively small space and expect it to work,” explains Drela. “We had to design an entirely new architecture with many innovations to the fan, diffusers, contraction, and the corner vanes to give the new tunnel our desired capabilities within the limits of the old tunnel’s existing footprint,” he added.
The new and original Wright Brothers tunnels are both closed-circuit designs, with air flowing through the test portion for measuring purposes before recirculating around the tunnel. The similarities, however, end there.
The new tunnel is radically different
Because the BLI fan is powered directly by a 2,500-horsepower (1864.25 kW) motor, the whole drive system has just one moving part, which is a substantial improvement over the old tunnel's mechanically complex variable-pitch drive. The motor speed is controlled by a variable frequency drive, which is more energy-efficient and quieter than the old tunnel system.
When the tunnel operates at maximum speed, the fan pressurizes most of the tunnel flow circuit, allowing the tunnel's far wall opposite the fan to sustain up to 80 tons of load, equivalent to the force of a 240-mph (386 kph) hurricane. The fan and the test section are the only sections of the Wright Brothers Wind Tunnel that are fixed to the ground to withstand the ensuing elastic flexing of the walls.
The tunnel's remaining supports are sliding and rocking, allowing it to "squirm" in position up to 1 centimeter, relieving major stress caused by pressure loads and temperature fluctuations.
The new tunnel will continue a significant history of representing AeroAstro in MIT and public outreach activities, much as its predecessor did. Other MIT instructors used the earlier tunnel to give classes and test other club equipment with student groups. Visitors can step into the test area and experience the wind tunnel in action with the air blowing at a breezy 30 mph (48 kph), which has always been a popular attraction during school events.