By Kelly Hahn
“I remember telling my parents at a very young age that I wanted to study fluid mechanics,” José Graña-Otero says with a chuckle. “I don’t know exactly why I said that, and I’m not sure I even knew what it was.”
Fluid mechanics is a branch of physics that tries to explain how liquids or gases move. Nearly all engineering disciplines use fluid mechanics and the subject is a required course for many of our students.
It is not normally a field of study that stirs the imagination of a young child.
Nonetheless, Graña-Otero is an assistant professor of mechanical engineering in the UK College of Engineering, a position he’s held since 2014. His specialty? Fluid mechanics with aerospace applications.
“Airplanes fly through air, and understanding how they do that requires fluid dynamics. Plus, airplane engines burn fuel, which is combustion. Combustion can be said to be fluid mechanics with chemical reactions, and it’s used in aeronautical sciences to produce power in jet engines and rockets,” Graña-Otero explains.
While Graña-Otero’s doctoral work involved combustion of gases, he recently received a $592,000 grant from the U.S. Air Force to apply his understanding of combustion to solids. Mechanical engineering associate professor Alexandre Martin, who also has an extensive background in fluid mechanics, will serve as co-investigator.
Spacecraft re-entering Earth’s atmosphere travel at a speed that, coupled with the high-temperature air outside the ship, poses a catastrophic threat to the craft. Fortunately, by applying a thin layer of material that slowly burns away as it interacts with oxygen, the structure can remain intact. This process of carbon oxidation isn’t new, but it turns out that knowledge of how it works—the intermediate steps of how the fluid dynamics interact with the chemistry—is slim.
“In order to be able to model how the materials gasify and disappear, you have to have access to all of the possible chemical reactions,” says Graña-Otero. “To my surprise, that information was almost totally lacking. That’s a problem because you don’t want to run out of material when you’re flying at hypersonic speed.”
Graña-Otero says another challenge for understanding exactly what happens lies in the many different scales involved.
“For the vehicle itself, which is usually quite large, you can apply classical fluid mechanics. But the basic processes that control oxidation occur at nanometer molecular scales. So when you get down to this level, you have to use quantum mechanics.”
As Graña-Otero’s Air Force grant indicates, building the knowledge base for safe hypersonic flight has not only military applications, but also commercial possibilities. According to Graña-Otero, hypersonic flight would allow someone to fly from the U.S. to Europe in just a couple of hours or even less. New York to London in the span of time it takes to watch a football game; is that really possible?
“Mach number refers to the speed of an object compared to the speed of sound. We currently can fly at Mach 3, or three times the speed of sound, but the goal is to reach Mach 10-20,” Graña-Otero answers.
Twenty times the speed of sound. Try to imagine it and you quickly discover you can’t. But José Graña-Otero can, and perhaps we shouldn’t be surprised. After all, he’s been dreaming about fluid mechanics for a long, long time.