Technical Details
For over 80 years, it has been an axiom in aerospace engineering that the smoother the surface of an aircraft or car, the lower the air resistance. This is why engineers have strived to create highly polished fuselages, wings, and skins. However, a new study has shown that this fundamental principle does not always hold.
Research Findings
A team led by Associate Professor Aiko Yakino from the Institute of Fluid Mechanics at Tohoku University (Japan) has demonstrated that specifically designed microscopic surface roughness can reduce aerodynamic resistance by up to 43.6%. The key effect is achieved because micro-roughness delays the transition of airflow from a laminar to a turbulent state.
New Technology
The new technology is called Distributed Micro-Roughness (DMR) — 'distributed micro-roughness'. Unlike known 'shark-like' coatings with directional grooves, DMR uses chaotic and random micro-roughness that is invisible to the human eye.
Experimental Setup
The main technological breakthrough was a unique experimental setup. Conventional wind tunnels require models to be mounted on supports and wires, which themselves distort the airflow and hinder accurate measurements of such small effects. Japanese engineers solved the problem using the world's largest magnetic suspension system, 1m-MSBS.
Experimental Results
The experiments showed that the critical Reynolds number — the moment of transition to turbulence — shifts from 1.9×10^6 to 2.2×10^6. In other words, the flow remains laminar for significantly longer.
Industry Impact
If the technology is scaled up for aviation, it could potentially lead to significant reductions in fuel consumption, operating costs, and carbon emissions. Currently, the Tohoku University team is working on further optimizing the shape and density of micro-roughness and trying to expand the range of speeds at which the effect remains maximum.