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 improved thermal protection systems and methods for joining materials is a long and expensive process. There are only a handful of wind tunnels in the world that can mimic the conditions of hypersonic flight.
Some of the world’s most advanced facilities are housed close to UTSI, within the Arnold Engineering Development Complex (AEDC) at Arnold Air Force Base—but the AEDC can cost hundreds of thousands of dollars to reserve and operates on a years-long waiting list.
“We have all these different kinds of wind tunnels that each specialize in examining some part of the hypersonic flight problem, but nobody has the capability to replicate full hypersonic flight conditions,” said UTSI and MABE Assistant Professor Mark Gragston. “There’s a big market for increased testing capability in academic research because that’s where new materials are being developed.”
Earlier this fall, Johnson, Gragston, and four other investigators from UT and the University of Dayton Research Institute embarked on a $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 US Air Force through the Air Force Research Laboratory (AFRL) in Ohio.
“We’re trying to be the bridge between AEDC and UT and make these tests more accessible,” Johnson said.
A Unique Intermediate
Officially, the grant is being headed by Johnson and MABE Assistant Professor Damiano Baccarella, an expert in hypersonic aerothermodynamics who has previously overseen construction of a hypersonic wind tunnel. However, the six investigators—experts in hypersonic flow modeling, 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.”
Over the next four years, the world-class team will oversee the construction of an unparalleled hypersonic wind tunnel facility and a multi-tiered workflow that should accelerate the discovery of new TPS materials.
The grant also funds graduate students to work under each of the participating investigators. These students will not only advance TPS material research but gain an incomparable understanding of the infrastructure behind a hypersonics facility.
“There are several types of hypersonics facilities, and you can learn how to build all of them from textbooks except for this kind,” Gragston said. “The students who are around while this is being built, and are helping build it, will have a truly unique opportunity.”
“Some of our students will learn how to make the materials and characterize them; Mark’s students 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.”
Enabling a Dynamic Workflow
Currently, new TPS candidate materials have to go straight from laboratory-scale tests to large-scale wind tunnel evaluations. The UTSI tunnel will change that.
“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 tell you whether a new material is worthy of those more expensive tests in a quicker time span and with less expense.”
Johnson and Baccarella’s team is also working to validate and improve simulations of TPS materials, which will further close the gap between ground-based tests and flight conditions. Those simulations will benefit from unparalleled testing capabilities at UTSI, like noninvasive, laser-based analysis of the chemical reactions around materials during testing.
Such diagnostic capabilities are uniquely available at UT because this is where they were developed—some by Gragston and another member of the team, MABE Professor Zhili Zhang.
“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.”
Contact
Izzie Gall (865-974-7203, egall4@utk.edu)