[mlmonkey]

> 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]

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.

[degamad]

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".

[kazinator]

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.

[kjkjadksj]

They don’t though. Hit your golf ball into the cart path and see what happens after. Pro or competitive golfer will toss it and use a new ball.

[beering]

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.

[coldtea]

However the TFA doesn't make clear that this: "It's long been accepted that the smoother the surface, the lower the aerodynamic drag. That turns out not always to be the case" was already known to NOT always be the case (e.g. in golf balls).

[Swizec]

> 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]

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

[ungreased0675]

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.

[coldtea]

>It slightly increased gas mileage and slightly reduced noise.

Between the day to day road conditions and different routes noise and the modest effect, I'd say this would be impossible to tell.

[cpncrunch]

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

[NetMageSCW]

Tough behind a paywall.

[bookofjoe]

https://archive.ph/YwAky

[cpncrunch]

Not seeing a paywall in safari. Try incognito.

[stasomatic]

Me too. Is it known by how much though in relatives percentage terms? Sometime things are just worth the effort. If larger than 20%… okay, but then if everyone uses dimpled balls (I understand they do), it’s just a thought experiment, then what’s the point. Why aren’t ping pong balls dimpled?

[Ekaros]

I read somewhere that it depends... Different shaped objects benefit from different surface effects. A rounded surface like ball benefits from dimples where as more straight surface like arrow would not. I have no idea but I could also guess that speed affects things.

[dathinab]

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)

[nmstoker]

And the Mig-29 too but according to the reply that's different