and a lot of "smooth" aerodynamic surfaces have "microscopic"/"very small" surface patterns to make the surface less perfect smooth as if it is too perfect smooth the air kinda "sticks" to it increasing drag (to say it in a very unscientific way)
If the application method is as rudimentary as sandblasting, it sounds rather simple to retrofit to existing aircraft. If it works as they state it does, it's a virtually free same-day fuel efficiency boost.
However, I did not see what the actual net improvement was. When they talk percentages, they are talking only about "in the transition zone". They say the coefficient improves throughout, but in theory, it could be almost irrelevant if the overall improvement throughout the profile is close to 0. It also sounds like a very difficult level of precise degradation to maintain for any period of time in real world conditions, since it would be easy to clog or abrade further.
Uhh. I was taught that in university in the late 80s. Some surfaces have a lot of friction and if you add surface imperfections the turbulent airflow actually reduces drag.
I wrote about this ages ago, in that shark skin is an evolutionary adaptation worth study because water is thicker than air, but when air compounds, blah blah blah. Basically think of making a composite mold with directional tiny tiny dorsal fin looking surface. If you rub your hand on it the wrong way it cuts you open. Could even be scaled for large cargo ship hulls.
Next up: my personal wing invention which uses leading edges modeled on humpback whale fins, because the use case / stall profile is better.
Sigh, I’m going to have a great time in Heaven chatting with Leonardo da Vinci…
> 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.
This article is kind of false. Keeping an object's boundary layer attached is known to reduce drag, even if the flow is turbulent. Golf ball dimples are a successful attempt to keep boundary layers attached.
The headline is perhaps overstating things a bit but they do discuss how this is different than e.g. rivulets
'''
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.
'''
Golf ball dimples are about 4 mm across and 0.2mm or 200μm (micrometers).
These features are several orders of magnitude smaller at 38 to 53μm diameter.
>>the first in the world to 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. [...] Two types of DMRs were used in this experiment: A convex pattern made of glass beads with diameters ranging from 38 to 53 micrometers (μm) and a concave pattern applied by sandblasting. The height of the DMR coating is only 1 percent of the thickness of the boundary layer and is classified as a “smooth surface” from a hydrodynamic point of view.
> It's long been accepted that the smoother the surface, the lower the aerodynamic drag. That turns out not always to be the case.
Huh... I'd always heard that a golf ball's dimples help reduce drag?
> Huh... I'd always heard that a golf ball's dimples help reduce drag?
Yep also vortex generators in cars have become common. So common that they've filtered down to after market parts you can put on a honda civic
Vortexes break up large air pockets and reduce drag.
TFA makes it clear that this is a very different phenomenon than golf ball dimples, and even goes as far as to say they are opposing.
yep
and a lot of "smooth" aerodynamic surfaces have "microscopic"/"very small" surface patterns to make the surface less perfect smooth as if it is too perfect smooth the air kinda "sticks" to it increasing drag (to say it in a very unscientific way)
If the application method is as rudimentary as sandblasting, it sounds rather simple to retrofit to existing aircraft. If it works as they state it does, it's a virtually free same-day fuel efficiency boost.
However, I did not see what the actual net improvement was. When they talk percentages, they are talking only about "in the transition zone". They say the coefficient improves throughout, but in theory, it could be almost irrelevant if the overall improvement throughout the profile is close to 0. It also sounds like a very difficult level of precise degradation to maintain for any period of time in real world conditions, since it would be easy to clog or abrade further.
https://archive.ph/DbcqV
Uhh. I was taught that in university in the late 80s. Some surfaces have a lot of friction and if you add surface imperfections the turbulent airflow actually reduces drag.
I wrote about this ages ago, in that shark skin is an evolutionary adaptation worth study because water is thicker than air, but when air compounds, blah blah blah. Basically think of making a composite mold with directional tiny tiny dorsal fin looking surface. If you rub your hand on it the wrong way it cuts you open. Could even be scaled for large cargo ship hulls.
Next up: my personal wing invention which uses leading edges modeled on humpback whale fins, because the use case / stall profile is better.
Sigh, I’m going to have a great time in Heaven chatting with Leonardo da Vinci…
From the featured article:
> 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.
This article is kind of false. Keeping an object's boundary layer attached is known to reduce drag, even if the flow is turbulent. Golf ball dimples are a successful attempt to keep boundary layers attached.
The headline is perhaps overstating things a bit but they do discuss how this is different than e.g. rivulets
''' 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. '''
Yes, but this is not that.
Golf ball dimples are about 4 mm across and 0.2mm or 200μm (micrometers).
These features are several orders of magnitude smaller at 38 to 53μm diameter.
>>the first in the world to 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. [...] Two types of DMRs were used in this experiment: A convex pattern made of glass beads with diameters ranging from 38 to 53 micrometers (μm) and a concave pattern applied by sandblasting. The height of the DMR coating is only 1 percent of the thickness of the boundary layer and is classified as a “smooth surface” from a hydrodynamic point of view.
"We apologize for the mistake in overturning a fundamental principle of aeronautical engineering, those responsible have now been sacked."