NASA Advances Pressure Sensitive Paint Research Capability

The Swept Wing Flow Test model, known as SWiFT, with pressure sensitive paint applied, sports a pink glow under ultraviolet lights while tested during 2023 in a NASA wind tunnel at Langley Research Center in Virginia.

NASA / Dave Bowman

Many of us grew up using paint-by-number sets to create beautiful color pictures.

For years now, NASA engineers studying aircraft and rocket designs in wind tunnels have flipped that childhood pastime, using computers to generate images from “numbers-by-paint” – pressure sensitive paint (PSP), that is.

Now, advances in the use of high-speed cameras, supercomputers, and even more sensitive PSP have made this numbers-by-paint process 10,000 times faster while creating engineering visuals with 1,000 times higher resolution.

So, what’s the big difference exactly between the “old” capability in use at NASA for more than a decade and the “new?”

“The key is found by adding a single word in front of PSP, namely ‘unsteady’ pressure sensitive paint, or uPSP,” said E. Lara Lash, an aerospace engineer from NASA’s Ames Research Center in California’s Silicon Valley.

With PSP, NASA researchers study the large-scale effects of relatively smooth air flowing over the wings and body of aircraft. Now with uPSP, they are able to see in finer detail what happens when more turbulent air is present – faster and better than ever before.

In some cases with the new capability, researchers can get their hands on the wind tunnel data they’re looking for within 20 minutes. That’s quick enough to allow engineers to adjust their testing in real time.

Usually, researchers record wind tunnel data and then take it back to their labs to decipher days or weeks later. If they find they need more data, it can take additional weeks or even months to wait in line for another turn in the wind tunnel.

“The result of these improvements provides a data product that is immediately useful to aerodynamic engineers, structural engineers, or engineers from other disciplines,” Lash said.

Robert Pearce, NASA’s associate administrator for aeronautics, who recently saw a demonstration of uPSP-generated data displayed at Ames, hailed the new tool as a national asset that will be available to researchers all over the country.

“It’s a unique NASA innovation that isn’t offered anywhere else,” Pearce said. “It will help us maintain NASA’s world leadership in wind tunnel capabilities.” 

A technician sprays unsteady pressure sensitive paint onto the surface of a small model of the Space Launch System in preparation for testing in a NASA wind tunnel.

NASA / Dave Bowman

How it Works

With both PSP and uPSP, a unique paint is applied to scale models of aircraft or rockets, which are mounted in wind tunnels equipped with specific types of lights and cameras.

When illuminated during tests, the paint’s color brightness changes depending on the levels of pressure the model experiences as currents of air rush by. Darker shades mean higher pressure; lighter shades mean lower pressure.

Cameras capture the brightness intensity and a supercomputer turns that information into a set of numbers representing pressure values, which are made available to engineers to study and glean what truths they can about the vehicle design’s structural integrity.

“Aerodynamic forces can vibrate different parts of the vehicle to different degrees,” Lash said. “Vibrations could damage what the vehicle is carrying or can even lead to the vehicle tearing itself apart. The data we get through this process can help us prevent that.”

Traditionally, pressure readings are taken using sensors connected to little plastic tubes strung through a model’s interior and poking up through small holes in key places, such as along the surface of a wing or the fuselage. 

Each point provides a single pressure reading. Engineers must use mathematical models to estimate the pressure values between the individual sensors.

With PSP, there is no need to estimate the numbers. Because the paint covers the entire model, its brightness as seen by the cameras reveals the pressure values over the whole surface.

A four-percent scale model of the Space Launch System rocket is tested in 2017 using unsteady Pressure Sensitive Paint inside the 11-foot by 11-foot Unitary Plan Wind Tunnel at NASA’s Ames Research Center in California.

NASA / Dominic Hart

Making it Better

The introduction, testing, and availability of uPSP is the result of a successful five-year-long effort, begun in 2019, in which researchers challenged themselves to significantly improve the PSP’s capability with its associated cameras and computers.

The NASA team’s desire was to develop and demonstrate a better process of acquiring, processing, and visualizing data using a properly equipped wind tunnel and supercomputer, then make the tool available at NASA wind tunnels across the country.

The focus during a capability challenge was on NASA’s Unitary Plan Facility’s 11-foot transonic wind tunnel, which the team connected to the nearby NASA Advanced Supercomputing Facility, both located at Ames.

Inside the wind tunnel, a scale model of NASA’s Space Launch System rocket served as the primary test subject during the challenge period.

Now that the agency has completed its Artemis I uncrewed lunar flight test mission, researchers can match the flight-recorded data with the wind tunnel data to see how well reality and predictions compare.

With the capability challenge officially completed at the end of 2024, the uPSP team is planning to deploy it to other wind tunnels and engage with potential users with interests in aeronautics or spaceflight.

“This is a NASA capability that we have, not only for use within the agency, but one that we can offer industry, academia, and other government agencies to come in and do research using these new tools,” Lash said.

NASA’s Aerosciences Evaluation and Test Capabilities portfolio office, an organization managed under the agency’s Aeronautics Research Mission Directorate, oversaw the development of the uPSP capability.

Source: NASA Advances Pressure Sensitive Paint Research Capability - NASA