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A fundamental principle of aeronautical engineering has been overturned

wired.com

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Re: A fundamental principle of aeronautical engineering has been overturned

#71

Post by degamad »

djeastm wrote: post #26
mlmonkey wrote: post #9

> 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?

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.

mlmonkey did not say that this new observation was the same phenomenon as golf ball dimples, just golf ball dimples already disproved the "long accepted" belief that "smoother the surface, the lower the aerodynamic drag".

Re: A fundamental principle of aeronautical engineering has been overturned

#72

Post by consp »

TomatoCo wrote: post #39
russellbeattie wrote: post #23

Earlier quoted context omitted.

> "...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.

On a metal as soft as copper I imagine that texture'll last about 30 minutes after it's issued to the soldier.

Doesn't the barrel remove this texture completely with the spin groves? Seems more of an issue than rough handeling.

Re: A fundamental principle of aeronautical engineering has been overturned

#73

Post by dotancohen » 

  > The ... magnetic support balance system ... can levitate a streamlined model ... inside a wind tunnel without contact using electromagnetic force.
That's pretty cool. Presumably the varying magnetic field strength required to suspend the test article is also an indicator of varying forces on the vehicle.

Re: A fundamental principle of aeronautical engineering has been overturned

#74

Post by [deleted] »

SilverElfin wrote: post #22
Swizec wrote: post #16

Earlier quoted context omitted.

> 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.

Is that what those things are on random civics? Do they make any difference for regular street cars?

[deleted]

Re: A fundamental principle of aeronautical engineering has been overturned

#75

Post by [deleted] »

dotancohen wrote: post #73

> The ... magnetic support balance system ... can levitate a streamlined model ... inside a wind tunnel without contact using electromagnetic force. That's pretty cool. Presumably the varying magnetic field strength required to suspend the test article is also an indicator of varying forces on the vehicle.

[deleted]

Re: A fundamental principle of aeronautical engineering has been overturned

#76

Post by kazinator »

degamad wrote: post #71
djeastm wrote: post #26

Earlier quoted context omitted.

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.

mlmonkey did not say that this new observation was the same phenomenon as golf ball dimples, just golf ball dimples already disproved the "long accepted" belief that "smoother the surface, the lower the aerodynamic drag".

Exactly; golf balls are one example of it not being accepted that smooth surfaces are always best for drag, regardless of how the new result works.

Re: A fundamental principle of aeronautical engineering has been overturned

#77

Post by [deleted] »

cpncrunch wrote: post #21
mlmonkey wrote: post #9

> 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?

Read the article….this is a completely different effect.

[deleted]

Re: A fundamental principle of aeronautical engineering has been overturned

#78

Post by [deleted] »

otterdude wrote: post #55
Maarten88 wrote: post #34

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 surprisi…

The core tenant of the paper is that roughness reduces drag IN the transition zone. A very small region of the total flow. Thats the region between laminar and turbulent flow. Laminar flow is typically 5x less drag than turbulent, and will be encountered about a Reynolds number of 500K-1M (ratio of inertial flow to viscous flow). Surfboards will have a Reynolds number of 10^7 which is entirely turbulent. A Cessna air…

[deleted]

Re: A fundamental principle of aeronautical engineering has been overturned

#79

Post by leptons »

sgc wrote: post #8

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…

The physics of travelling at 600mph+ would affect the rough surface differently than at 60mph. Airplane wings experience erosion due to the high speed combined with particles in the air - dust, ice, volcanic ash, and rain/water. The erosion is a problem that sees significant mitigation. If the surface were made to be rough I'd expect some unexpected results, and it may even become a bigger problem. I do think the technique should be tested though.

Re: A fundamental principle of aeronautical engineering has been overturned

#80

Post by larusso »

Maarten88 wrote: post #34

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 surprisi…

I thought that shark skin foil was a thing for years. Where they tried to emulate the micro roughness of shark skin.
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