There are ideas so entrenched that they are hardly questioned. For example, the notion that, if you want a plane to cut through the air as efficiently as possible, its wings must be perfectly smooth. It seems like irrefutable logic, and in fact, it has always been so: the smoother a surface is, the less drag it will encounter as it moves.
Theoretically this has been one of the foundations of modern aerodynamics, taken into account by manufacturers, engineers and researchers. Now a group of Japanese scientists has just arrived at a conclusion that seems to contradict eight decades of research: a small dose of roughness could be better than a flawless surface. And the theorem is being dismantled, or so they claim.
Turbulence, Always the Enemy
To understand the topic and the finding, one must first understand something much more basic and primordial in the world of aviation: when an airplane advances, the air flows around its wings forming a thin region known as the boundary layer. While that flow remains orderly and stable, aerodynamic drag stays relatively low. The problem arises when turbulence begins.
Turbulence, which are nothing more than perturbations, end up transforming into increasingly larger vortices that force the aircraft to expend more energy to keep moving. The idea has always been the same, and the solution, obvious: eliminate any irregularity that could alter the airflow. But researchers at Tohoku University decided to explore a different possibility.
The Japanese technique, officially named ‘DMR’ or ‘Distributed Micro Roughness’, uses tiny irregularities (so minute as to be barely perceptible to the naked eye), microstructures less than 50 micrometers deep (roughly the thickness of a human hair) to slightly alter the air flow in the region closest to the wing.
They tested several configurations: while some used tiny glass spheres applied to the surface, others used microcavities created by sandblasting processes.
The Secret Is to Make the Surface Rough, But Almost Invisibly
The explanation of the phenomenon is paradoxical, because instead of generating more turbulence, what these micro-irregularities do is create a series of perturbations so small that they hinder the formation of larger ones. It would be something like, if the air flow received thousands of tiny jolts that prevent oscillations from growing into significant vortices.
Or, more technically, the system delays the transition from laminar to turbulent flow. Translated into simpler language: the air remains orderly for longer. According to the Japanese, this allowed reducing aerodynamic drag by 43.6%.
For the skeptics, the tests were conducted in the world’s most advanced wind tunnels, those at Tohoku University where models are suspended by a magnetic levitation system rather than conventional supports. That way, they can measure with surgical precision.
However, there is still time before seeing it (or not, because it is microscopic) in commercial airplanes. Moreover, there is a problem: if these microstructures are so important, any accumulation of dirt could alter their functioning. It remains to be seen whether in practice it works as well. The advancement already exists, at least.
Images | FedEx, Pexels
