Faster than the speed of sound

Researchers study effects of rain, ice, and aerosols on hypersonic vehicles

In recent years, the United States aerospace and defense industry has become increasingly invested in vehicles traveling at hypersonic speed, or more than five times faster than the speed of sound. But what happens when an object travels that fast? College of Science and Engineering professors Tom Schwartzentruber and Graham Candler are working with multiple universities across the country to find out.

Hypersonic vehicles travel at speeds higher than Mach 5, or more than 3,800 miles per hour. For reference, a commercial airplane cruises at speeds ranging from 460 and 575 miles per hour. A hypersonic vehicle can be a plane, missile, or spacecraft—such as a satellite re-entering Earth’s atmosphere or a vessel landing on Mars.

Research facilities at government laboratories and other universities typically use wind tunnels to study flights at normal and even supersonic speeds. But, it can be nearly impossible to physically re-create hypersonic flight conditions in these wind tunnels. Schwartzentruber and Candler’s labs in the University of Minnesota's Department of Aerospace Engineering and Mechanics specialize in computational hypersonics, which entails creating computer simulations to study these high-speed flights.

“For hypersonic flight, experiments are very difficult,” Schwartzentruber explained. “So then, doing computer simulations is very useful to understand what’s happening and to design these vehicles properly.”

The two CSE professors, along with their collaborators at the University of Maryland, University of Illinois, University of Hawaii, and Stevens Institute of Technology, recently received a five-year, $7.5 million Multidisciplinary University Research Initiative (MURI) grant from the Office of Naval Research (ONR) to study how small particles—such as raindrops, ice crystals, or aerosols—impact hypersonic flight.

Engineering a new perspective

While hypersonics isn’t a new concept, what often isn’t considered in the research is what happens when these vehicles fly through small particles in a planet’s atmosphere.

“These vehicles already need special materials because they’re flying so fast and getting so hot,” Schwartzentruber said. “But now, you have particles that are hitting the material at kilometers per second. This is a project to really try to understand the damage that these particles can cause.”

The research findings could impact future aircraft designs for the U.S. Air Force and NASA—and answer such questions as: Would a Mars probe burn up in the Martian atmosphere? How would the probe fare while landing in a dust storm? Would ice crystals crack or damage the heat shields of hypersonic military planes?

Schwartzentruber and Candler are the perfect team to do this work. Schwartzentruber’s lab focuses on the molecular—modeling collisions between molecules and atoms—and Candler’s lab looks at the mechanics of fluids.

“Generally speaking, my group’s expertise is at the very high altitudes as you approach space, and Graham’s group is focused on lower altitudes where you can use fluid mechanics,” Schwartzentruber explained. “So, it’s kind of a natural project for both of us.”

According to the professors, it’s collaboration that makes the University of Minnesota a world leader in the field of hypersonics.

Last year, Candler played an important role in establishing a countrywide University Consortium for Applied Hypersonics—a five-year, $20 million per year U.S. Department of Defense initiative involving industry, national laboratories, and many of the nation’s top research universities to develop hypersonic technologies.

“It’s all about collaboration,” said Candler, who is a Distinguished McKnight University Professor and recently elected member of the National Academy of Engineering. “I wouldn’t be as recognized as I am without working with Tom. That’s why we lead, because we’ve built a group that has a really interesting mix and match of different capabilities.

It’s all about hiring the right people, having the right environment for people to flourish and be successful, and of course getting the right students,” Candler said.

The pair are working with professor and aerosol expert Chris Hogan in the Department of Mechanical Engineering on this study. They also frequently collaborate with CSE chemistry professor Donald Truhlar.

“The science problems are incredibly interesting and difficult,” Schwartzentruber added. “It’s not just that it’s some hypersonic vehicle that NASA needs some help cobbling together. It’s what happens to a liquid droplet traveling at two kilometers per second as it flies through a shock wave. The amount of fluid mechanics and computational science and chemistry that you need to understand—that helps pull people in, when they realize how challenging the problem is, it makes for a fun environment.”

To learn more about U of M aerospace research, visit the Department of Aerospace Engineering and Mechanics website

Story by Olivia Hultgren

If you’d like to support research in the University of Minnesota College of Science and Engineering, visit our CSE Giving website.