A Fundamental Principle of Aeronautical Engineering Has Been Overturned (wired.com)
(Tuesday May 26, 2026 @11:30PM (BeauHD)
from the rough-around-the-aero-edges dept.)
- Reference: 0183424872
- News link: https://science.slashdot.org/story/26/05/27/0014254/a-fundamental-principle-of-aeronautical-engineering-has-been-overturned
- Source link: https://www.wired.com/story/a-fundamental-principle-of-aeronautical-engineering-has-been-overturned/#intcid=_wired-verso-hp-trending_b091cb9c-265c-4787-bab8-d94fb1ae6f85_popular4-2
An anonymous reader quotes a report from Wired:
> Aerodynamic drag is a major "barrier" in high-speed airplanes, automobiles, and bullet trains. This is because a design with less aerodynamic drag allows the aircraft to move at higher speeds with less energy. When an aircraft or car body moves at high speed, a thin layer of air called the " [1]boundary layer " is formed on its surface. This boundary layer has two states: laminar flow, in which air flows in an orderly fashion, and turbulent flow, which involves turbulence. The longer the air stays in the laminar flow state with low friction, the smaller the air resistance becomes, but as the air speed increases, it transitions to turbulent flow. The key to reducing aerodynamic drag is how to delay this transition to turbulence.
>
> For more than 80 years, the principle of "the surface of an object must be smooth" has been the basic premise of aeronautical engineering throughout the world in order to suppress the transition to turbulence and reduce aerodynamic drag. This premise was based on the results of a 1940 study by Ichiro Tani, a Japanese aerodynamicist who quantitatively demonstrated the relationship between "surface roughness" (an indicator of the state of the machined surface) and turbulent transition, arguing that surface roughness, which was unavoidable with the manufacturing technology of the time, prevented laminar flow from being realized. However, in 1989 Tani reinterpreted the experimental data on rough-surface pipes obtained by fluid engineer Johann Nikulase in the 1930s, bringing a new perspective that "roughness may not necessarily only promote turbulent transition and increase fluid resistance." Inheriting this idea, a research group led by Yasuaki Kohama of Tohoku University experimentally demonstrated in the 1990s that fibrous rough surfaces, which have fine fibrous irregularities on their surface, have the effect of delaying transition under certain conditions.
>
> The same Tohoku University research team recently [2]announced a discovery that significantly advances this trend. Aiko Yakino, associate professor at Tohoku University's Institute of Fluid Science, and her research group were the first in the world to [3]demonstrate that aerodynamic drag can be reduced by up to 43.6 percent simply by applying distributed micro-roughness (DMR), a surface roughness so fine and irregular that it cannot be distinguished by the naked eye. This technology is fundamentally different from the "rivulet (shark skin) process," which is known as a typical aerodynamic drag reduction technology. The rivulet process mimics the fine longitudinal grooves in shark skin, and by carving grooves approximately 0.1 mm wide along the direction of airflow, it aligns the vortices that occur near the wall surface of turbulent airflow areas. DMR, on the other hand, delays the switch from laminar to turbulent flow by means of random and minute irregularities. The flow zones it affects and the mechanisms it employs are based on completely different concepts.
[1] https://en.wikipedia.org/wiki/Boundary_layer
[2] https://www.tohoku.ac.jp/japanese/2026/05/press20260512-02-DMR.html
[3] https://www.wired.com/story/a-fundamental-principle-of-aeronautical-engineering-has-been-overturned/#intcid=_wired-verso-hp-trending_b091cb9c-265c-4787-bab8-d94fb1ae6f85_popular4-2
> Aerodynamic drag is a major "barrier" in high-speed airplanes, automobiles, and bullet trains. This is because a design with less aerodynamic drag allows the aircraft to move at higher speeds with less energy. When an aircraft or car body moves at high speed, a thin layer of air called the " [1]boundary layer " is formed on its surface. This boundary layer has two states: laminar flow, in which air flows in an orderly fashion, and turbulent flow, which involves turbulence. The longer the air stays in the laminar flow state with low friction, the smaller the air resistance becomes, but as the air speed increases, it transitions to turbulent flow. The key to reducing aerodynamic drag is how to delay this transition to turbulence.
>
> For more than 80 years, the principle of "the surface of an object must be smooth" has been the basic premise of aeronautical engineering throughout the world in order to suppress the transition to turbulence and reduce aerodynamic drag. This premise was based on the results of a 1940 study by Ichiro Tani, a Japanese aerodynamicist who quantitatively demonstrated the relationship between "surface roughness" (an indicator of the state of the machined surface) and turbulent transition, arguing that surface roughness, which was unavoidable with the manufacturing technology of the time, prevented laminar flow from being realized. However, in 1989 Tani reinterpreted the experimental data on rough-surface pipes obtained by fluid engineer Johann Nikulase in the 1930s, bringing a new perspective that "roughness may not necessarily only promote turbulent transition and increase fluid resistance." Inheriting this idea, a research group led by Yasuaki Kohama of Tohoku University experimentally demonstrated in the 1990s that fibrous rough surfaces, which have fine fibrous irregularities on their surface, have the effect of delaying transition under certain conditions.
>
> The same Tohoku University research team recently [2]announced a discovery that significantly advances this trend. Aiko Yakino, associate professor at Tohoku University's Institute of Fluid Science, and her research group were the first in the world to [3]demonstrate that aerodynamic drag can be reduced by up to 43.6 percent simply by applying distributed micro-roughness (DMR), a surface roughness so fine and irregular that it cannot be distinguished by the naked eye. This technology is fundamentally different from the "rivulet (shark skin) process," which is known as a typical aerodynamic drag reduction technology. The rivulet process mimics the fine longitudinal grooves in shark skin, and by carving grooves approximately 0.1 mm wide along the direction of airflow, it aligns the vortices that occur near the wall surface of turbulent airflow areas. DMR, on the other hand, delays the switch from laminar to turbulent flow by means of random and minute irregularities. The flow zones it affects and the mechanisms it employs are based on completely different concepts.
[1] https://en.wikipedia.org/wiki/Boundary_layer
[2] https://www.tohoku.ac.jp/japanese/2026/05/press20260512-02-DMR.html
[3] https://www.wired.com/story/a-fundamental-principle-of-aeronautical-engineering-has-been-overturned/#intcid=_wired-verso-hp-trending_b091cb9c-265c-4787-bab8-d94fb1ae6f85_popular4-2
Woah, cool (Score:3)
by T34L ( 10503334 )
It's not that surprising that someone found another exception to the the rule of thumb that's been proven wrong with many mechanisms at many scales, including the shark skin, but also just, golf ball dimples, and all kinda wacky methods on aircraft wing like shock bodies and all...
...I'm more impressed they now got air friction tunnels that levitate the object magnetically a meter out, against the air friction, while also being able to actually measure the drag on it at that. That's really, really cool and oughta open up aerodynamics to lot of experiments that'd be very difficult to pull off without compromising accuracy or something else.
Hence it was not a "fundamental" principle (Score:2)
by gweihir ( 88907 )
It was a generally accepted principle. Please stop with the abuse of language to make things sound more flashy. It just makes you look dumb.
Mythbusters? (Score:3)
Did not the Mythbusters show that dimples could reduce drag (S7E14)? Sure, not exactly the same, but it should not have taken 17 years for the research to catch up (or maybe someone finally watched Golf Ball Car?)
Re: (Score:2)
The article even mentions that there's other surface irregularities that decrease friction, and the paper mentions other methods that also decrease drag, but the newly observed effect is distinct and different with the ones we've seen so far, and the headline is reductionist and bad.