UTSI Secures $17.8M Hypersonic Wind Tunnel to Accelerate TPS Development
On reentry, space shuttles slam into Earth’s atmosphere at nearly Mach 25 (25 times the speed of sound). That tremendous speed heats the shuttle’s surface above 2600 degrees Fahrenheit, and subjects it to similarly extreme pressure, for up to 15 minutes.
While spacecraft reentry is the most extreme example, all hypersonic vehicles—anything that travels above Mach 5—must contend with high temperature and pressure for extended periods. The most vulnerable parts of these vehicles, such as the nose and leading edges of wings, are covered in specialized heat-resistant materials called the thermal protection system (TPS).
“The TPS is not continuous. Every joint between tiles, or even the glue that sticks the TPS to the fuselage, is a weakness,” said materials scientist Jacqueline Johnson, a professor in the Department of Mechanical, Aerospace, and Biomedical Engineering (MABE) at the University of Tennessee Space Institute (UTSI). “We have had two glaring examples of what happens when the TPS is weak or damaged in the Challenger and Columbia space shuttle disasters.”
Developing and improving TPS materials is a long and expensive process requiring time in the world’s most advanced wind tunnel facilities, such as those housed within the Arnold Engineering Development Complex (AEDC) near UTSI—where the wait list is several years long and a test campaign can cost millions of dollars.
“There’s a big market for increased testing capability in academic research because that’s where new materials are being developed,” said UTSI and MABE Assistant Professor Mark Gragston.
Last fall, Johnson, Gragston, and four other investigators from MABE and the University of Dayton Research Institute (UDRI) embarked on a four-year, $17.8 million grant to create a new wind tunnel at UTSI that can subject material samples to hypersonic conditions for up to tens of minutes. The facility and accompanying research are funded by the United States Air Force through the Air Force Research Laboratory (AFRL) in Ohio.
“If a subpar material fails tests at the AEDC, that’s a huge waste of money and time,” said Gragston. “We’re building an intermediate-scale capability that could quickly tell you whether a new material is worthy of those more expensive tests.”
Multi-Tiered Hypersonics Workflow
This AFRL grant is the latest step in UTSI’s plan to turn Tennessee into a hypersonics powerhouse.
“In 2014, the leadership of AEDC and UT launched an initiative to spark growth in hypersonics on our campus,” said UTSI Executive Director John Schmisseur. “They recognized it as a great opportunity for us to respond to a national need, and through the process, to foster greater collaboration and partnership.”
The unparalleled wind tunnel will exemplify that sense of collaboration, as the six investigators—experts in hypersonic flow modeling, hypersonic aerothermodynamics, materials development, experimental flow diagnostics, and wind tunnel testing—will hold equal authority as the project moves forward.
“This team was carefully chosen to bring different aspects together, and nobody is trying to be the boss,” Johnson said. “There’s a lot of work to do and it cannot be done by UTSI alone.”
We have more advanced measurement capabilities at UT than what is usually available in the facilities at AEDC and the National Aeronautics and Space Administration.”
The team will also be improving simulations of TPS materials, further closing the gap between ground-based tests and flight conditions. To validate those simulations, the team will utilize noninvasive, laser-based analysis of the chemical reactions around materials during testing—a method developed at UT—and other unparalleled testing capabilities at UTSI.
“We have more advanced measurement capabilities at UT than what is usually available in the facilities at AEDC and the National Aeronautics and Space Administration,” Gragston said. “We’re going to be applying many of them to this hypersonic testing environment for the first time.”
Statewide Impacts
As part of UTSI’s long-term plan for Tennessee, the new Air Force grant also supports development of the state’s hypersonics workforce.
Graduate students working under each of the participating investigators will not only advance TPS material research but gain an incomparable understanding of the infrastructure behind a hypersonics facility.
“Some of our students will learn how to make the materials and characterize them; some will be doing diagnostics; some of them will be heavily involved in developing the actual facility, learning alongside our facilities people,” said Johnson. “All of them should be well equipped to work in the aerospace industry by the time they’re done with this project.”
Like the hundreds of TPS tiles protecting a vehicle reentering the atmosphere, individual researchers, students, and even the wind tunnels themselves are all vital components of Tennessee’s burgeoning hypersonics sector.
“If you think about UT’s land grant mission, then people across the state should benefit from what happens in the Space Institute,” Schmisseur said. “It’s not just materials, it’s not just structures, it’s not just aerodynamics; it’s how all of them integrate into a system that can efficiently do its job under the extreme conditions of high-speed flight.”