Textured surfaces & aero - 2012

[superdread]

Could it be that the main issue with rain is that it makes the air denser (through cooling it and maybe water spray) and that makes it more likely to detach?

[olefud]

Could it be that the main issue with rain is that it makes the air denser (through cooling it and maybe water spray) and that makes it more likely to detach?

It might be the other way. Water is a dipolar molecule that “wets” the surface, i.e. clings thereto. Perhaps the original observation was that a wetted surface was somewhat rougher and improved attachment. This could lead to purposeful roughing of the surface.

[superdread]

Could it be that the main issue with rain is that it makes the air denser (through cooling it and maybe water spray) and that makes it more likely to detach?

It might be the other way. Water is a dipolar molecule that “wets” the surface, i.e. clings thereto. Perhaps the original observation was that a wetted surface was somewhat rougher and improved attachment. This could lead to purposeful roughing of the surface.

How good a fluid wets a surface is a question of surface tension (of the fluid) and water, as a quasi macro-molecule, has a high one (that's why it forms droplets on a smooth surface in contrast to e.g. vegetable oil). So the rough surface could help break these up. A wetted surface is smoother than the underlying one (because the surface tension forces the fluid to a minimal surface area).

Maybe the water droplets create tiny vortices hampering the flow.

P.S. I got it the wrong way around some posts ago. A rougher surface lowers the effective contact angle, therefore makes it easier to create a continuous fluid film (i.e. wets the surface).

[bigpat]

It has to do with bith boundary layer, and surface tension of fluids.

A polished surface tends yo make fluids bead, due to high surface tension. This is acceptable on thd the upper surface of a wing, as it is the high pressure/ slower velocity side.

A wet and dry finish( generally 1200-2000 grit) provides a 'blemish free surface', nog necessarily polished ( this is the important part), with creates less surface tension in fluids. At high speeds, on coming air is essentially acting like a vuscous fluid, so this 'might' have an effect of increasing the velocity of aur floeing under the wing, increasing the difference in pressure between the two sides.

The wet sanding is used extensively on yachts, big and small. The hull, rudders and keels being regularly sanded between regattas. There is as an optimum surface roughness, between 800-2000 grit. I think generally 3000 is getting too fine to have any effect.

The true way to check fof a good finish is not the sheen, as it will always look dull. Rather, to hold the object up to the light, where it will reflect like a mirror if finished well. By right, the underneath of the front wing wojld need constanf attention, considering all thd stonechips, and nicks it wiold suffer. Also raw carbon fibre doesn't really give the best finish due the non suitability of sanding back into the carbon yarns. A painted surface that is sanded is better....

[marcush.]

hm in water efects are apearing at slower speeds .so there might be something in it.

[superdread]

Air is a gas (mixture), it has no surface tension. so no urge to form minimal surface areas.
Water has it and a rough surface effectively lowers it where the fluid meets the solid surface, breaking up droplets.

[marcush.]

Air is a gas (mixture), it has no surface tension. so no urge to form minimal surface areas.
Water has it and a rough surface effectively lowers it where the fluid meets the solid surface, breaking up droplets.

what about humidity ?

[superdread]

Air is a gas (mixture), it has no surface tension. so no urge to form minimal surface areas.
Water has it and a rough surface effectively lowers it where the fluid meets the solid surface, breaking up droplets.

what about humidity ?

Humidity is water in aerosol form, i.e. vapour. The minuscule droplets have no cohesive force between one another, so no surface tension.

[marcush.]

I´m inclined not to draw conclusions too quickly.
The effects are there for different reasons than we might be able to imagine but one can only try to ask more questions and see what a conglomerat of brains can come up with ..

[ffangio]

Also, just quoting "a source" means it's probably rubbish.

I heard from a guy at Red Bull that they are using triple f-ducts activated by the driver's left earlobe.
Don't ask me who the source is though... hmmm...

[ChipAyten]

I'm sure its widely known that uneven surfaces at high speeds has less aero drag than a smooth one. But has it ever been considered in F1? Take for instance sharks, their skins are comparable to a fine grit sandpaper. What happens is within the peaks and troughs of the surface pockets of water convect. Because of this water then glides against water, and the coefficient of water on water is a lot less than water on shark skin. This principal is the same for gasses, it's why golf balls have dimples in them. Would air on air friction compared to air on paint/carbon fiber yield slightly faster lap times?

Thoughts?

[hollus]

Never say never, but there is a reason this hasn't appeared as of yet.

Anyways, this has been discussed before.
viewtopic.php?f=6&t=881&hilit=golf

[marcush.]

in fact ,sharks skin was used as sandpaper not too long ago ...

we hear RedBull are using it already(not to sand the surfaces but to help aero)

I´m pretty sure i read about aeroplane (Airbus Industries ) using specially formulated paints these days mimiking the effects.

the paint also has favourable thermal behaviour if I´m correct..
http://www.fraunhofer.de/en/press/resea ... ystem.html

[bhall]

Aerodynamic riblets:

Riblets are small surface protrusions aligned with the direction of flow, which
confer an anisotropic roughness to a surface. They are one of the few techniques that have been successfully applied to the reduction of the skin friction in turbulent boundary layers, both in the laboratory and in full aerodynamic configurations.
(Links to PDF)

[hollus]

Current last post in the RB8 thread.

http://www.omnicorse.it/magazine/22796/ ... -biomimica

The coach of Red Bull Racing being photographed with meticulous new discharges of RB8 is the 'race engineer Sebastian Vettel. It's called Guillaume Rocquelin, and is a Frenchman who has graduated from the University of Grenoble in the team led by Adrian Newey is not only in charge of intellectual work.

Today, before the third free practice session, the Alps had to deal with a mysterious roll pastry under the wing lower back, that, so to speak, where there is the blow that runs the Super-DRS Red Bull Racing.

Guillaume spent a few minutes to spread this particular matter that has an aerodynamic function very specific: the particular roughness of pasta, in fact, should help to increase efficiency. It is a solution that is used in a particular way in the nautical and tends to reproduce the flakes wrinkled skin of the shark that generate a turbulent flow useful to reduce the cross section of the wake and thus drag.

The Biomimica, as you call this type of research that comes from the observation of animals in nature, can be very useful in the development of fluid dynamics: the Red Bull Racing that is sensitive to all forms of innovation is also along this road in an attempt to improve the performance of the RB8.

Is it true or just a rumor?