Null winds: Wheel fairing test/ video

[daves302gt]

Hey all,
Been lurking on here awhile, gathering knowledge before I start my own project, 'Aero-off-road'. Off road vehicles often have relatively open and exposed wheels so while googling that I found this company that makes bicycle wheel fairings and there is a very interesting video demonstration of how vehicle speed/ headwinds affect wheel drag. It's not groundbreaking, but does help reinforce what we already know.

Apparently I can't post links but if you manually enter it, maybe someone with more posts than I can put it in a follow up post on this thread

Null winds 'dot' com 'slash' technical

Enjoy!

[sheepdog 44]

Null Winds Technology

Interesting.

[NachtRitter]

Funny... the first thing I thought of when I saw the pic is a skirt guard (see Skirt guard - Wikipedia, the free encyclopedia), something that's been around for at least 40 years and probably many more. Usually they were made from mesh or strings, but I'd also seen solid ones as shown in the rear of the bike on the Null Winds site.

[kach22i]

Originally Posted by sheepdog 44

Null Winds Technology

Interesting.

We should take time to note that thrust/wind coming off of an axial fan is in a swirling motion, not straight back and straightened - even with those modest vane guards.

If in doubt, I'll let anyone stand behind my hovercraft and experience the flow; downward on the left side, and upward on the right side.

I've designed my splitter and diverter accordingly.

That table top fan is no substitute for a wind tunnel.

[daves302gt]

kach22i,
What do you think that might change in this experiment? How much downward or upward force is on the front of each wheel, thus the direction it's tendency is to turn?

[elhigh]

The demo has merit, and it just echoes what lots of people have been saying here for a long time: wheels are draggy. Smooth out as much of the airflow over them as possible.

I can't remember who said it or in which thread, but I liked one answer to the wheel drag question: skirt the wheel well, and add smoothie discs to the wheels too. One reduces the air resistance experienced by the wheel itself, and the other reduces the skin drag of the entire body. Win-win.

With your offroader, you'll have to get a little creative. Your tires may project beyond the body line, so skirting the wheel wells may not be a viable option, or it has to be a modest one. If everything is done with a stock look so the tire shoulders don't project, then skirts are an option but you'd still want to be able to remove them easily when you get to the mudholes. Probably the same goes for any wheel discs you add, since if you leave them on then the wheel will just pack up with mud behind the disc.

Air dams might be helpful, and some belly pans. If you're into hard rock trails then belly pans shouldn't be a problem, but if you're a mudder then again I would strongly recommend designing something that is easily removed before hitting the holes.

[daves302gt]

For the rear wheelwell skirt, i was thinking about a skirt that came down like an eye-lid over an eye... with the eye being the tire. It would bump out the frontal area a little, but it would be smooth flowing down the side of the truck. I just need to figure the right geometry so it tucks up and out of the way but is rigid enough to not flap in the wind on the highway.

I agree with removable stuff, I'm thinking a sizeable air-dam primarily, then cleaning up the underside with a belly pan, like you also said. Definitely an aero bed cover integrated with the roll cage. I mostly only think / dream about this stuff because I haven't had time to actually work on it! I'll let you guys know if I have any aero-progress.

[kach22i]

Originally Posted by daves302gt

kach22i,
What do you think that might change in this experiment? How much downward or upward force is on the front of each wheel, thus the direction it's tendency is to turn?

I'm not sure I would change anything in the experiment given it illustrates clearly the differing effects of the swilling force coming off of the fan blades as the height of the wheels behind it are elevated and lowered into the swill.

Explanation here although the images are small - go to page.
A discussion of side and down thrust by Gibbs Guides

This picture of a WW2 Corsair clearly shows that the prop imparts a swirl to the airflow, causing it to hit the fin at an angle. This produces a yawing force, typically causing the nose to want to swing to the left

Link to another small image , this one by Michael Balter:
http://www.gbrcaa.org/ntoa/Page%204%...20set%20up.htm

Water is similar:

http://www.ivorbittle.co.uk/Articles...0for%20net.htm

It clearly shows the rotating flow pattern that tells us that the propeller is producing thrust and it shows the tip vortices.

http://www.simerics.com/gallery_propeller

Propeller:

A propeller is essentially a type of fan which transmits power by converting rotational motion into thrust for propulsion of a vehicle such as an aircraft, ship, or submarine through a mass such as water or air, by rotating two or more twisted blades about a central shaft.(From wikipedia)

[ennored]

I think you're all missing the basics. Relative to the ground (and air) the top of a wheel is traveling at twice the road speed. The bottom is not moving.

Fairing the top half will have MUCH higher gains than doing the bottom.

[kach22i]

On the topic of wheel farings, I found this image to be interesting.

2008 Barcelona Testing - April - Forum - F1technical.net


Caption from next page in link:

It's a very common method of showing airflow

its basically kerosene with some dye mixed in the kerosene evaporates away leaving the dye behind showing the airflow path

at the speeds f1 cars travel the air dosent really compress anyway

EDIT-1: Hummgh.........strange...
http://fakeferrarinews.wordpress.com...nd-other-news/

It is still a matter of debate whether these strange wheel attachments are indeed an aero device, a measuring device, a satelite system, or a tv signal booster, perhaps only time will tell. Personally we were hoping for some spikes out the side to shred the oppositions tyres, but you know we can’t have it all and we are prone to getting carried away with things on the odd occasion.

Edit-2..................it's about brake cooling.
http://www.formula1-dictionary.net/wheel_shrouds.html

We witnessed significant rule change for 2010. The wheel shrouds have been banned after a couple of incidents last season where they came off at speed.

Originally Posted by ennored

I think you're all missing the basics. Relative to the ground (and air) the top of a wheel is traveling at twice the road speed. The bottom is not moving.

Fairing the top half will have MUCH higher gains than doing the bottom.

It would be interesting if the flow were straightened, just saying.

As it is now, I cannot even start to separate out the different forces and reach a conclusion.