Surface Structure and aerodynamics

[paul-collins]

I was just perusing Mulsanne Corner, and looking at the LMR (specifically for Mike's aero analysis), and it got me wondering. Are cars today designed with any microstructure in the surface?

At the Ontario Science Centre, they have this cute little display with two balls of the same weight, one a golf ball and the other smooth, and showing which has more wind resistance (hint - they didn't change golf ball design after seeing this experiment). Obviously this experiment illustrates wall-bounded turbulence, providing laminar airflow closer to the surface than would normally occur for a smooth surface.

I just saw an article on sharkskin riblets, that discussed use of this in pipes.

So, is this something that could be implemented in cars? Would it be effective over 24 hours, or would cleaning be required?

[C_g]

interesting thoughts!

[Osella]

I read about this somewhere else, the concept was to have a sensor and a tiny 'pore' secreting water droplets over the surface of a car.
I believe Ford are working on it in the US.

Also, in F1, didn't the original Brabham BT46A (don't know if this was a fan-car or not) have heatsinks on the body in place of radiators? It didn't work and I'm not sure anyone has tried again since. Aerodynamics have come on a bit since then. Must be worthy of further investigation!

hey, I've just read the article, v. interesting. Very tempting to go and get something relatively well understood, like a 911GT3 or Viper, and see if a hairy on was any better!

[egor]

I know they have tried different coatings on aircraft wings/tailplanes in the past. One I aircraft I have worked on had the tailplanes painted with a rough tecture coating similar to the non slip paint you get on steps etc.
This was ment to allow the air molicules to grip the surface and create a much smoother surface than can be achived by paint.

They also use forced air flow over the leading adge of the wing to increase air flow/lift over the wing at lower speeds.

[KC]

This same aerodynamics lesson is being used in fighter jets and extreme acrobatic aircraft as well. As much money as racing spends on aerodynamics they'll figure out a way to exploit it soon.

[TVRfan]

the rear wing were building has dimples in. i have heard of them being on bonnets aswell, apperently the saleen's of Graham Nash had spares with them on. thet've been around for some time tho. It is amazing how much they work tho, on a rear wing we dropped from 0.32 to 0.28!

[paul-collins]

Which wing is that?

[MulsanneMike]

I've been surprised that small vortex generators have not been utilized in motorsports in critical areas such as wings, front nose diffusers, etc. There is nothing that would ban them in the rules and they seem very practical, allowing a wing to operate more efficiently for example. And understand these aren't new devices, they've been used in the aviation industry for years, 40+. Though in aviation, they are traditionally used when a design doesn't function as hoped and are more a stop gap solution. So in avaition they have a stigma, though the documentation seems to show that they will improve inefficient designs as well as make good designs work even better when properly fitted and tested.

[C_g]

The Toyota GT-One used a lot of vortex generators. This new Reynard seems to have a few too.

[MulsanneMike]

Not the kind I'm talking about, small surface mounted VGs along the lines of dimples or even http://www.computer-certainty.com/ (click vortex generators). Recall Mulsanne's was the first to point on vortex lift possibilities on the GT-One...

http://www.mulsannescorner.com/gtone101.htm

Using car architecture to generate vortexs isn't new. Champ cars have been using that methodology for some time now:

http://www.mulsannescorner.com/LolaUnderbody.jpg

But I have yet to see small, surface mounted VGs in use in motorsports.

[norman-normal]

I remember when Jim Hall first used the rear wing, every one knew it would work but couldent adjust and builders were very slow to use it. I think shiny race cars will be here a while longer. Hobie cat sailors were using this tech 15 yrs ago, but I see the Americas Cup boats bottoms are very smooth; any one know why?

[Nordic]

So if I don't wash my car again, the dirt molecules that build up over the years will both increase my top speed and MPG.
Or the next time I hit a badger or fox the resulting hair & blood on the frontal vortex generator(Bumper) will also have the same effect?
good to know.

[norman-normal]

In a word Yes. This is not new tech. About a century ago, when golf had a smooth surface, they noticed that old balls with a rough, cut up, surface flew further and straighter: hence, the dimples. Enlightend race engine builders determined (about 20 yrs ago) that head porting increased HP but polishing did not(a lot of "experts" arn't aware of this). A surface like 800 grit sand paper seems to be best. Haven't you noticed fighter aircraft?

[cybersdorf]

Originally posted by Nordic
Or the next time I hit a badger or fox the resulting hair & blood on the frontal vortex generator(Bumper) will also have the same effect?
good to know.

That's badger engineering for you.

[MulsanneMike]

Well yes and no actually. If you left the entire surface "dirty" you'd run into an increase in form drag. The main thing about using sand paper, vgs, etc., is proper placement. You'd only want to place these devices in areas where the boundary layer could separate as it works to increase the energy in the boundary layer, thuse delaying separation. So less is more in this case.

[TVRfan]

its because the air 'sticks' to the smooth surface. i overheard some boy racers the other day and one was saying how it took him 2 days to polish his heads and exhaust manifolds and he could 'feel the difference'. ok. whatever mate. the smoother the surface the more sticky it becomes

[norman-normal]

Thanks Mike. My info is mostly "hands on" from building engines-race cars many years ago. I would be greatfull current info on the subject....Back then we knew some things worked but wern't sure why. It seemed as though the rough surface could hold a boundry of air that allowed the high velocity air faster passage. But then few of us had much formal education and in those days we could find nothing on the subject

[Brant]

Err, so does this mean the dimples are little area's of low pressure, causing the air to more closely follow the surface. Or have I got this all wrong.

[manicmechanic]

I read or heard somewhere that the ALMS was or is considering the use of vortex generators on the underwing of the LMP cars, has anyone heard if this is true and when will we see it?

[norman-normal]

I don't know Brant and it seems no one else does. This is a developing technology. One of the problems is that the military does not like to release information. Its interesting to note that water behaves in a similar fashion; no doubt you have heard of a sharks skin feeling like sandpaper

[Nordic]

Following your advice,I have cleaned stragic parts of my car, the results while not yet fully collected seem to point to a small increase in top end on the run into work today, the MPG remained the same.
If any of you would like to spectate I shall be doing the 'downhill' run on the M23 at about 4pm tonite.

Have a happy and peaceful Christmas one and all

[cybersdorf]

So now we know why Santa has a beard.
Merry Christmas everybody!

[Dauntless]

This thread brings to mind an observation I have made several times on my race car. After wet track sessions, I have noticed the streaking left from droplets creeping along the surfaces, indicating adherence. In other areas the droplets are unstreaked, which I presume indicated detached air flow. I am planning a track session next month, and would like to investigate this more thoroughly. Can anyone recommend a specific type of oil to use? I plan to place droplets in a grid, go out for a track session, and then record the results. Maybe this can lead to using small VGs to re-attach flow where I want it.

Thanks! Stan