Future passenger jets could use microscopic vibrations hidden beneath their surfaces to reduce air resistance and burn less fuel, according to new research that challenges a century-old approach to aircraft design.
When a passenger jet travels at around 640 mph (1,030 kilometers per hour), air flowing over its wings can become turbulent.
This turbulence increases drag, forcing the aircraft’s engines to work harder and consume more fuel.
Since a commercial jet can burn more than 10,000 gallons (37,900 liters) of fuel during a cross-country flight, even modest improvements in efficiency could produce significant savings.
Researchers led by Mahmoud I. Hussein at the University of Colorado Boulder are developing a different way to tackle the problem. Instead of changing the external shape of an aircraft, they want to engineer materials underneath its smooth surface that interact with airflow through extremely small vibrations.
The research centers on phonons, tiny vibrations that travel through materials. Hussein has spent more than two decades helping develop the field of phononics, which seeks to understand and control these vibrations.
In 2015, Hussein introduced the idea of “phononic subsurfaces,” or PSubs. These specially designed materials sit beneath a surface and can manipulate vibrations in ways that affect the fluid flowing above them.
Until now, one major limitation was that PSubs generally worked at only a single vibration frequency. Real-world turbulence, however, involves many frequencies.
In research published in Physical Review X, Hussein’s team demonstrated a phenomenon called “super-resonance.” By designing the internal phononic structure in a coiled shape, the researchers found they could influence a much broader range of frequencies.
That could make the technology far more useful under real flight conditions, where airflow constantly changes.
A second advance, reported in Proceedings of the Royal Society A, tackles another important challenge: controlling turbulence farther downstream.
The researchers found that multiple PSubs could be arranged together in a grid or lattice. Through a phenomenon they call “scatterless interference,” the structures could work together to weaken disturbances as they travel across a larger surface.
This could potentially allow turbulence to be delayed across much more of an airplane wing or even along the body of a high-speed vehicle.
Combining the two discoveries could address two of the biggest obstacles facing the technology: controlling many frequencies at once and extending that control over a larger area.
The research remains computational, so the concept has not yet been demonstrated on a passenger aircraft. However, physical PSub prototypes have already been built by research groups around the world, and scientists are working toward testing their performance in wind tunnels.
The long-term goal is to create aircraft with normal, smooth outer surfaces while engineering the material underneath to interact with airflow in carefully controlled ways.
The idea could eventually extend far beyond aviation. Similar technology might help control turbulence around ships, inside pipelines and in turbines.
If the approach works under real-world conditions, future engineers may be able to improve aerodynamics not just by changing an object’s shape, but by carefully controlling the microscopic vibrations hidden inside it.
