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Maarten88 22 minutes ago [-]
Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid.
It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction.
Now the surprising question to me is how is it possible that something so simple was not known in this very well-researched and well-funded field. It probably was known, just not by the paper-publishing researchers.
Groxx 35 minutes ago [-]
It's almost certainly my adblocker playing poorly with their "subscribe to read" stuff, but I had to lol at the failure mode. When I load the page, I get the splash image/headline, and below it:
> Subscribe to listen [9 minutes]
> 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.
And then just comments and links to other articles. No indication at all that there's more to the article beyond (apparently) an audio recording.
This might explain some of the "didn't read the article" comments? Not that it doesn't happen anyway tho.
mlmonkey 3 hours ago [-]
> 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?
djeastm 50 minutes ago [-]
From the article:
>This principle is fundamentally different from the effect of dimples on golf balls. Dimples reduce pressure resistance by intentionally turbulizing the airflow and suppressing backward separation. DMR, on the other hand, delays the transition, thereby suppressing not pressure resistance but the wall friction itself. They are opposite mechanisms.
beering 3 hours ago [-]
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.
cpncrunch 1 hours ago [-]
Read the article….this is a completely different effect.
NetMageSCW 38 minutes ago [-]
Tough behind a paywall.
Swizec 3 hours ago [-]
> 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.
SilverElfin 1 hours ago [-]
Is that what those things are on random civics? Do they make any difference for regular street cars?
ungreased0675 1 hours ago [-]
I put some (actual, as in from an airplane parts catalog) vortex generators on my hybrid. It slightly increased gas mileage and slightly reduced noise.
The less aerodynamic the vehicle, the more noticeable the result will probably be.
dathinab 3 hours ago [-]
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)
pfdietz 3 hours ago [-]
[dead]
aaron695 41 minutes ago [-]
[dead]
sgc 4 hours ago [-]
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.
… theoretically meets reality pretty quick in aviation. You’ll likely find a lot of red tape to modifying any particular aircraft until it has been tested or certified. Well, for certified aircraft anyway. Even in the experimental world you might find some (excuse the pun) resistance to sand blasting someone’s wing.
zonkerdonker 2 hours ago [-]
Based on the mechanism of flow attachment in the transition zone it seems like the overall airfoil profile would likely have to change to take full advantage of the reduced friction. I think its much more likely to see this technique played with somewhere like Formula 1, if it hasnt been already.
russellbeattie 1 hours ago [-]
> "...like Formula 1"
Or projectiles like bullets and missiles. A sniper bullet with nanoscale textured surface that's able to go x% farther due to reduced drag seems plausible.
TomatoCo 42 seconds ago [-]
On a metal as soft as copper I imagine that texture'll last about 30 minutes after it's issued to the soldier.
I'll await the experimental measurements of fuel efficiency using real aircraft.
drpixie 7 minutes ago [-]
Me too. The number of "revolutionary" designs that are announced but disappear makes me cynical. Looking wings on real aircraft, unless freshly painted, they're pretty close to finely sanded :) If the airlines and engineers saw a significant performance degradation with wear, they'd be out there polishing and repainting wings.
On a similar note - How many times have you seen announcements about someones blended wing that is going to save 50% fuel? But there are very few blended wings in nature (eg. rays), and those are in a very slow-speed regime.
dnautics 2 minutes ago [-]
The real obstacle to blended wing designs, I imagine, is more boring: airports are likely to be difficult to retrofit to support those, well for cargo anyways, and for passengers there's probably less appetite to board such a plane
dnautics 3 minutes ago [-]
Is this not useful in the speed regime of automobiles?
4 hours ago [-]
qwertyuiop_ 2 hours ago [-]
Tell that to the ice build up on the wing.
rawgabbit 3 hours ago [-]
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.
clnhlzmn 60 minutes ago [-]
You learned something different then because this finding is that some kinds of additional roughness delay the transition to turbulent flow which is pretty clear in the article.
6stringmerc 3 hours ago [-]
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…
r3trohack3r 3 hours ago [-]
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.
spacedoutman 16 minutes ago [-]
>humpback whale fins
you might find this video interesting then, the fastest rc drone in the world and it uses humpback inspired props.
Why wait for heaven. There probably are mods for Kerbal Space Program with exactly that parts. Create your wingsuit there.
bediger4000 7 hours ago [-]
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.
staplung 4 hours ago [-]
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.
'''
toss1 4 hours ago [-]
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.
nullhole 44 minutes ago [-]
Not to be that guy, but 38-53um is 1 order of magnitude smaller than 200um
toss1 32 minutes ago [-]
Not to be that guy ;-) , but the diameter of the golf ball dimples is ~4 mm or about 4,000 μm, whilst the diameter of the spheres is 38-53 μm, or about 0.04 mm.
Diameter-to-diameter seems like about 100x or two orders of magnitude?
Similarly, 200 μm is the golf ball dimple depth (oops, just noticed I dropped that key word), and they didn't give us a measurement of the depth of the dents caused by the spheres or sandblasting, but it would likely be significantly less than half the radius of the spheres?
Sorry about misleading with dropping the "depth" word.
doginasuit 4 hours ago [-]
"We apologize for the mistake in overturning a fundamental principle of aeronautical engineering, those responsible have now been sacked."
It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction.
Now the surprising question to me is how is it possible that something so simple was not known in this very well-researched and well-funded field. It probably was known, just not by the paper-publishing researchers.
> Subscribe to listen [9 minutes]
> 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.
And then just comments and links to other articles. No indication at all that there's more to the article beyond (apparently) an audio recording.
This might explain some of the "didn't read the article" comments? Not that it doesn't happen anyway tho.
Huh... I'd always heard that a golf ball's dimples help reduce drag?
>This principle is fundamentally different from the effect of dimples on golf balls. Dimples reduce pressure resistance by intentionally turbulizing the airflow and suppressing backward separation. DMR, on the other hand, delays the transition, thereby suppressing not pressure resistance but the wall friction itself. They are opposite mechanisms.
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.
The less aerodynamic the vehicle, the more noticeable the result will probably be.
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)
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.
Or projectiles like bullets and missiles. A sniper bullet with nanoscale textured surface that's able to go x% farther due to reduced drag seems plausible.
On a similar note - How many times have you seen announcements about someones blended wing that is going to save 50% fuel? But there are very few blended wings in nature (eg. rays), and those are in a very slow-speed regime.
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.
you might find this video interesting then, the fastest rc drone in the world and it uses humpback inspired props.
https://www.youtube.com/watch?v=k9n1h0rn9No
''' 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.
Diameter-to-diameter seems like about 100x or two orders of magnitude?
Similarly, 200 μm is the golf ball dimple depth (oops, just noticed I dropped that key word), and they didn't give us a measurement of the depth of the dents caused by the spheres or sandblasting, but it would likely be significantly less than half the radius of the spheres?
Sorry about misleading with dropping the "depth" word.