Airplane wings are typically made of smooth metal surfaces — a design that has worked well for decades on aircraft ranging from commercial airliners to fighter jets. However, materials science and manufacturing advances have created new opportunities to engineer more sophisticated aircraft surfaces that interact with and control airflow in new ways.
Experimental methods of flow control typically use active solutions, such as adding jets or other moving parts. However, active solutions add weight, complexity, cost and require more energy use.
Yulia Peet, an associate professor of aerospace and mechanical engineering in the Ira A. Fulton Schools of Engineering at Arizona State University, is leading a team of researchers to explore passive methods of flow control.
The team aims to gain a new understanding of how turbulent air flows interact with surfaces. The researchers will then design specially engineered metamaterials that influence flows in ways that can achieve high performance gains without the drawbacks of active solutions.
“We will generate a lot of new knowledge about these materials’ interactions with fluids such as airflow,” Peet says. “We’re trying to take it a step further by not only characterizing the fundamental physics but also seeing if we can go all the way through to fabricating those materials and testing them.”
Peet is collaborating with Lorenzo Valdevit, a professor of materials science and engineering and mechanical and aerospace engineering at the University of California, Irvine, and Kenny Breuer, a professor of engineering at Brown University, to study this new use of metamaterials for aerospace applications.
The research team is supported by a three-year, $2.25 million grant from the Air Force Office of Scientific Research National Science Portal Initiative to accelerate multidisciplinary scientific research of critical need to the U.S. Department of Defense, including new solutions for interactions between air and surface materials. The opportunity also focuses on increasing the diversity of people involved in research and the aerospace and defense workforce.
“Every exciting research project that I can think of is interdisciplinary,” Valdevit says. “Working in multi-university teams enriches everyone’s experience, both intellectually and culturally. I very much look forward to working with this great team on this exciting project.”
Disrupting flows for better performance
Peet brings expertise in characterizing and modeling the physics of flows and how they interact with materials. For this project, she was inspired to look more closely at flow separation and how this often-detrimental aspect of aerodynamics can be mitigated for improved performance.
When a plane is flying, it essentially makes the air “stick” to it as the airflow follows along a wing surface. Certain changes in turbulent airflow or the angle of flight can cause the flow to separate from the wing surface. When this happens, an aircraft can lose lift or experience increased drag or other undesirable effects.
One way to influence flow and suppress separation is by harnessing the frequencies present in the airflow. Like sound waves, air motions contain waves of different frequencies that result in different pressure signals on surfaces.
“We can optimize these interactions to make air vehicles move faster or consume less energy or make them quieter,” Peet says.
However, there isn’t a lot of information available about exactly which frequencies to target and how the team can alter them to interact with flow separation in useful ways.
“It’s a very difficult phenomenon to study and characterize all of these interactions between materials and fluids, especially when the fluids are turbulent like during an aircraft flight,” Peet says. “Computers have not been powerful enough and numerical methods haven’t been developed to the point that we need them to be. Now we’re starting to enter an era when this research becomes possible.”
Once Peet and the research team better understand which frequencies lead to separation, they can figure out how to create specially designed resonant metamaterials that can influence these frequencies. This is one of the goals for the team’s research.