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When the speed of sound isn’t fast enough, there is hypersonic travel — speeds five times the speed of sound. Doing so is quite possible. Engines have been designed to do so for at least a decade. 

But for those engines to operate optimally, there’s a world of physics challenges. That’s where Jeffrey Doom, an associate professor in the mechanical engineering department at South Dakota State University, comes in. This summer he will make his fourth trip to the Air Force Research Laboratory at Wright-Patterson Air Force Base near Dayton, Ohio, to undertake simulations and observe physical experiments.

Delaney Baumberger, a first-year graduate student from Blair, Nebraska, will join him.

They will be there June 2 to Aug. 8 as part of the Summer Faculty Fellowship Program through the Air Force Office of Scientific Research. Doom also participated in 2021, 2022, and 2023. The 10-week program gives him the opportunity to use simulation codes available at AFRL and other tools not available to Doom through his research at ����ֱ��app using its high-performance computing center.

Plus, there is the opportunity to tap the minds of some of the world’s foremost researchers in the field of computational fluid dynamics.

The fellowship covers the cost of transportation there and back as well as a stipend, from which the researchers provide their own housing. Doom’s wife will be there some of the time, but his teenage boys (Jonathan and Joseph) will stay in Brookings to work, and his daughter Kaitlyn is a student at ����ֱ��app, majoring in biology. So, the logistics can be somewhat of a challenge, he said.

Doom relishes time at AF research lab

But as for the science sector, Doom feels like a kid in a candy store.

What does he enjoy about it? “All of it. The challenge of the physics is the fun part of it. Going to Mach 5 produces major shock waves and is traveling five times faster than the speed of sound. The combustion process going that fast creates many issues. Getting fuel to mix at high-speed flow is very difficult; having it ignite in a timely manner before it exits out of the engine is a challenge. Developing all these simulation tools. Using commercial codes to help us out with that, too. There are endless challenges, but it’s fun,” he said.

Doom works on simulations for hypersonic engines during the school year, too. Thirty percent of his contract is tied to research, and he serves as the aerospace engineering specialization coordinator within the college. 

However, the Air Force Research Lab has “all the capabilities and financial backing to run these experiments where a university does not. It is very expensive; millions of dollars to run one lab. We will see all the open-source experiments that are available. “They have quite a few published open-source experiments that you will be able to see,” Doom said.

Baumberger plans peer-reviewed paper

They also will be able to see and discuss classified work, but that won’t be part of any paper Baumberger produces from her summer.

For Baumberger, who is eyeing a career in the aerospace industry, the short-term end goal for this summer is to produce a peer-reviewed paper that can be presented at a meeting of the American Institute for Aerospace and Astronautics.

Another master’s degree student, Matt Sorenson, is also working on this technology, too. During Doom’s 2021 and 2022 summer fellowships, he was joined by then-����ֱ��app doctoral student Zachary Chapman, along with Doom, wrote a computational fluid dynamics computer code that could be used to operate engines that run at supersonic/hypersonic speeds.

Chapman now works for an aerospace company, CFD Research, in Alabama.

Another student who gained his doctorate while working with Doom on this research was Mohammed Touimi in the fall 2024, and is currently working as a postdoc in France. 

Doom, who teaches senior- and graduate-level classes in turbomachinery, aerodynamics, and gas dynamics, said he can bring back classroom illustrations from his summer research. Also, he has built close relationships with the lab’s senior research aerospace engineers, Tim Ombrello and Dave Peterson.

“Tim Ombrello does a one-hour Zoom seminar for my students, and they absolutely love it,” Doom said.

Ramjet or scramjet?

Doom explained that the engines for hypersonic flight differentiate themselves from rocket engines in that rocket engines require their own oxidizer and fuel. Engines for hypersonic flight travel or “scramjets” ingest air at Mach 5 or greater, where Mach 1 is traveling at the speed of sound, which is around 770 mph. 

“At ����ֱ��app, we want to study scramjet engines. That encompasses design of the cavity flame holder, what types of fuels to use, the injection of biofuels and hydrogen fuels, getting a better fundamental understanding of fuel injection, where should I inject the fuel, how big should the cavity be, and what geometric shape should the cavity be,” Doom said.

He adds, “All the physics involved can cause a lot of issues with the engine. We’re trying to understand the physics as best as we can.  

“Students can also work on the exterior of the engine. When you’re going at Mach 5, the materials can get very hot. So, there is material science. How can these materials handle the hot temperatures without burning up? There are many great research questions for students to ask.”

Through the Summer Faculty Research Fellowship, Doom and Baumberger will not only be able to ask the questions. They will be able to see some of the answers.

Editor’s note: The September edition of Engineering Connections will feature a sit-down interview with Baumberger on her Air Force Research Lab experiences.