Ultra-ever-dry, good for aerodynamic reasons too?

[Nando]

[youtube]http://www.youtube.com/watch?v=z5L_vPkorBU[/youtube]
[youtube]http://www.youtube.com/watch?v=IPM8OR6W6WE[/youtube]

I found it interesting when he said the coating grabs air molecules and hold them which is what causes this effect where nothing really grabs on. (TED video)

So my question is if there would be any aerodynamic benefits of having air interacting with air rather then the car except for air that goes into intakes etc.

Does it even make a difference if air is hitting air or air hitting the bodywork directly?

[Drewd11]

Sounds like it would just create more of a boundary layer. It's well understood that attached air tends to create turbulent flow near to surfaces, which create a larger boundary layer of attached airflow, which would tend to increase drag since the turbulent attached layer of air will provoke turbulent flow near the surface.
I think that this would not be a successful drag-reducing coating to apply to an aerodynamic surface, since a thicker boundary layer tends to increase drag coefficient and decrease wing efficiency. The only application that occurs to me is to apply it to a lift generating area to compromise the airflow over that particular piece of bodywork but this would be a very tricky thing to optimise since airflow downstream would have less energy.
Anyways, I'm only an undergrad physics student, so what would I know, hopefully someone with actual knowledge can weigh in.

[Nando]

Thanks for the reply, with 130 views i was afraid i just asked the dumbest question in the world
I really have no idea about aerodynamics other then what has been picked up in certain places but had to ask at least.

[Drewd11]

Essentially, if I've understood correctly this is actually an inherently draggy compound, but that's not to say there aren't areas that wouldn't benefit from a thicker boundary layer, I just can't think of any atm.

[Holm86]

I think it could work. The turbulence is helping the boundary layer to stay attached. Dont know if it would have any mesurable effect on drag on an F1 car with the coating vs one without.

But perhaps it could be used on diffusers and wings to allow steeper angles without the flow seperating.

It should work just like the golfball dimples. They also create smalle vortices that maintain the boundary layer so there is not such a big low preassure area behind the ball.
This is sort of the same just in nano scale.

But its the same concept of the sharkskin swinsuits which also was hydrophobic. And swimmers gained alot of time by swimming with those. They are now banned. Though water is more draggy than air so the gain procentage would be higher in water than air.

[Drewd11]

I think it could work. The turbulence is helping the boundary layer to stay attached. Dont know if it would have any mesurable effect on drag on an F1 car with the coating vs one without.

But perhaps it could be used on diffusers and wings to allow steeper angles without the flow seperating.

It should work just like the golfball dimples. They also create smalle vortices that maintain the boundary layer so there is not such a big low preassure area behind the ball.
This is sort of the same just in nano scale.

But its the same concept of the sharkskin swinsuits which also was hydrophobic. And swimmers gained alot of time by swimming with those. They are now banned. Though water is more draggy than air so the gain procentage would be higher in water than air.

First, drag through water using this sort of compound is completely different since what produces the lower drag is the barrier between air and water creating an exceedingly smooth surface which reduces drag. I thought about use in diffusers and under front wings but there's a calculation here which we can't make because we don't know the loss of kinetic energy that would result and the corresponding loss of volumetric flow through the diffuser.

[Holm86]

I think it could work. The turbulence is helping the boundary layer to stay attached. Dont know if it would have any mesurable effect on drag on an F1 car with the coating vs one without.

But perhaps it could be used on diffusers and wings to allow steeper angles without the flow seperating.

It should work just like the golfball dimples. They also create smalle vortices that maintain the boundary layer so there is not such a big low preassure area behind the ball.
This is sort of the same just in nano scale.

But its the same concept of the sharkskin swinsuits which also was hydrophobic. And swimmers gained alot of time by swimming with those. They are now banned. Though water is more draggy than air so the gain procentage would be higher in water than air.

First, drag through water using this sort of compound is completely different since what produces the lower drag is the barrier between air and water creating an exceedingly smooth surface which reduces drag. I thought about use in diffusers and under front wings but there's a calculation here which we can't make because we don't know the loss of kinetic energy that would result and the corresponding loss of volumetric flow through the diffuser.

I know its more effective in water. But the concept still works with air. The question is just if its enough to make a real difference.

[tathan]

Might it have a bit of an effect at keeping flow attached in exhaust coanda effect if it thickens the boundary layer?

Failing that, pretty epic urinal.

[flyboy2160]

...But the concept still works with air...

Nope. Watch the video again. The liquid shedding/non sticking is due to the surface tension effect. That's not present with airflow.

[Drewd11]

...But the concept still works with air...

Nope. Watch the video again. The liquid shedding/non sticking is due to the surface tension effect. That's not present with airflow.

Much better put, that was precisely my point, thanks flyboy.

[Dragonfly]

In the video we see the coating interacting with liquids. And the air molecules layer which is said to be formed on the surface is preventing them from adhesion/wetting. As it was said, it's a kind of tension effect, and it seems to me such coating would not have the same effect when interacting with air or any gas.

[Gee]

Hi,

Something I can contribute to a little bit as I am just completing a PhD on whether such surfaces can be used to reduce drag in WATER.

The concept of my research is that if you make a surface superhydrophobic and immerse it in water, you can hold a layer of air on the surface. This theoretically has an effect on the viscous drag of the surface due to the change in viscosity between air and water.

To explain this take a basic definition of shear stress (which is directly proportional to the viscous drag)

Shear stress = viscosity x velocity gradient

So when you have water flowing past a superhydrophobic surface, with air trapped on it, the shear stress is proportional to the viscosity of the air rather than the water. You essentially have a lubricating layer of air, which has ~100x smaller viscosity, making your shear stress smaller and hence reducing the drag.

Thus, these surfaces cannot be used in air in this way as you would be lubricating air with air, which would clearly have no effect.

The problem for using these surfaces in water is that retaining an air layer on the surface is very hard. The air is subject to shearing forces, dissolves into the water over time, is affected poorly by contaminants etc etc. The upshot of my research is that you can achieve a drag reduction in water, but only if you can maintain a thick layer of air on the surface.

I hope that explains a bit, tried to condense my thesis into half a page . Let me know if you have any specific questions.

Cheers
Gee

[Nando]

that pretty much answers everything, brilliant stuff. thank you!

[Hobbs04]

Last year James Allen interviewed Christian Horner regarding his partnership with Infiniti/Nissasn and one of the topics of research was self healing paint. Horner said they were actually interested. This was on a podcast. I'll try and track it down.

[Blanchimont]

Does anyone know how ultra-ever-dry surfaces behaves when dirt is thrown at them with high velocity?

I'm asking because at the end of a grand prix the cars always look dirty and are covered with flies and marbles, which of course changes the surface roughness and maybe the airflow over these areas.

@Gee: How durable are the air layers you research in your thesis and with which methods do you produce them?