Associate professor Ibrahim Guven, Ph.D. from the Department of Mechanical and Nuclear Engineering is conducting a research project funded by the Department of Defense (DoD) that explores building aircraft for military purposes and civilian transportation that can travel more than five times the speed of sound. Guven’s role in this project is to consider the durability of aircraft surfaces against elements such as rain, ice, and debris. His research group is composed of Ph.D. students who assist with the study and has collaborated with other institutions, including the University of Minnesota, Stevens Institute of Technology and the University of Maryland.
Why did you get involved with this research project?
The intersection of need and our interests decides what we research. I’m interested in physics and have been working on methods to strengthen aircraft exteriors against the elements for 12 years. We started with looking at sand particle impact damage, and then we graduated from that to studying raindrop impact because that’s a more challenging problem. Sand impact is not as challenging in terms of physics. A liquid and a solid behave differently under impact conditions. The shape of the raindrop changes prior to the impact due to the shock layer ahead of the aircraft. Researching this impact requires simulating the raindrop-shock layer interaction that gives us the shape of the droplet at the time of contact with the aircraft surface. Unlike with sand, analyzing raindrop impact starts at that point, which requires accurate modeling of the pressure being applied. As the aerospace community achieves faster speeds, there’s a need to understand what will affect a flight’s safety and the aircraft’s structural integrity. That need is what I’m helping to fulfill.
Were there any challenges you and your research group faced while working on this study? How did you overcome them?
Finding data was hard. I’m a computational scientist, meaning I implement mathematical differential equations that govern physics to write computer code that predicts how something will behave. My experiments are virtual, so to ensure that my models work well, I need experimental data for validation. However, conducting experiments on this problem is extremely challenging. That’s the roadblock. Currently, we refer to data from the seventies and eighties. Beyond that, this kind of information is not available. We are working to generate data that my computational methods need for their validation. An example is the nylon bead impact experiment. Some researchers found that if you shoot a nylon bead at a target, it leads to damage similar to that from a raindrop of the same size. It is much easier and cheaper to shoot nylon beads compared to the experiments involving raindrops. However, this similarity vanishes as we go into higher velocities.
How do you typically gather data for a project of this nature?
We are working with a laboratory under the U.S. Navy. They can accelerate specimens to relevant speeds, meaning they can shoot them into the air at the desired velocity. A colleague at Stevens Institute of Technology also came up with a droplet levitator. He uses acoustic waves emitted by tiny speakers to play a certain sound at a certain frequency to create enough air pressure to suspend droplets midair. To an untrained eye, it looks like magic. They levitate droplets and use a railgun to shoot our samples at the droplets. Our samples hitting the droplets are stand-ins for the aircraft surface material. Once this is done successfully, they shoot a sample with high-speed cameras that can take ten million frames per second. As a result, we get a good, high-fidelity picture of this impact event. That is the type of data I’m seeking, and this is how I get it from my collaborators.
What was your overall experience working with the students in your research group?
I like to think it was positive. I try to be a nice advisor and give them space to explore, fail, and bring their own ideas. Even if I feel like we’re at a dead-end, I step back and let them figure it out. My role is to help them grow. Teach them, train them and help them along the way. That’s the experience.
Did you notice any personal changes in your students during this project?
Yeah, I have. When they’re just out of their undergraduate programs, confidence is lacking sometimes. You see them become more sure of themselves as they learn more and more. Often, regardless of whether English is their native language or not, writing is a big issue for every student. How one presents ideas in written form is a persistent problem in engineering. I see the most growth in that area. Again, an advisor has to be a guide and also have patience. Eventually, after working on multiple paper drafts, I can see tremendous improvement. You must allow them to see their shortcomings. It’s important to work with students to refine how they frame a problem, explain it to a wide audience in concise terms, and use neutral language without leading them to certain conclusions.
Why do you think that this research is important?
Somebody has to do it, right? I believe that I’m the right person because of my background. Personally, I think if this research makes for safer travel conditions, and if I have something to offer, then why not? If we can accurately simulate what happens in these conditions, we can use our methods to test out designs for damage mitigation. For example, we can perform simulations with different surface materials for the aircraft to see if using a different material or layered coating system leads to less damage. In a bigger picture, we’re working on a very narrow problem in our field, but we don’t know how useful that’s going to be in 10, 15 or 30 years from now. Whatever we study and put out there in terms of publications, it may help some other researcher in a different context many years later. This could be space research, modeling an atmosphere on a different planet, or something that is related to our bodies. There are parts of physics in this problem that do not necessarily only apply to high-speed flight. It could be many different things. One has to understand that what is studied may seem obscure today, but because the universe is more or less governed by the same physics, everything should be put in a theoretical framework, done right and shared with the community. People may learn things that could become relevant in the future. It’s not uncommon.
What is another subject that you plan to study?
The next natural step is coming up with strategies to mitigate damage in these scenarios. If avoiding a risk is not an option, can we actually come up with a solution? We have to determine how to modify an aircraft’s design to prevent a catastrophe. Another extension of my research would be to examine the landing of spacecraft on dusty planetary bodies. During landing on Earth, aircraft approach and reach the ground very smoothly. On the other hand, a spacecraft comes down slowly and needs a lot of reverse propulsion for a soft landing. As it does, it kicks up a large amount of dust, which blows back and hits the spacecraft. Taking into account the damage that occurs due to particle impact is a direct connection to my work. This again is an open area, and because we have ambitions to have a permanent presence on dusty places like the moon and Mars, we have to nail down the concept of landing safely. That is where my research could help.
