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19bonestock88 05-21-2018 06:32 AM

Just an idea...
 
1 Attachment(s)
While my car is gonna be apart for bodywork, I considered buying some lawn edging and adding an air dam, and then I had a brain fart...

Why not try and make front and rear wheel air curtains?

kach22i 05-21-2018 08:28 AM

Give it a try, worse thing that could happen is it does not work as imagined and you have to remove it or block it off.

From what I've read these things are extensively tested and not shot at from the hip.

Shoot from the hip, what the heck.

The rear elements look similar to what is seen on semi-tractor trailers, perhaps they could be longer and at a gentler angle?

The front chamber looks like one of those bernoulli/venturi diagrams that explain pressure and velocity.

https://anjungsainssmkss.wordpress.c...in-air-flight/
https://anjungsainssmkss.files.wordp.../bernoulli.jpg

Aren't most air-curtains big mouth, small exit?

There is an energy consumption factor or "work done" when squeezing and unsqueezing air. Energy/drag considerations.

Maybe do what you can to merely redirect air and not work it too much either way?

19bonestock88 05-21-2018 08:45 AM

I did alternately think about skipping the tire spat and just angling the side skirt from inside of front tire to outside of rear tire... I also meant to draw a little bigger gap in the front design, but I doodled it in like 45sec

freebeard 05-21-2018 12:11 PM

What are the relative heights of the component parts?

Air curtains are for steerable wheels. Do you have rear-wheel steering? Else skirts.

The rear wheel 'curtain' as drawn is occluded by the side curtain anyway.

Vman455 05-21-2018 02:19 PM

The one problem I see is, every air curtain I've looked at on a production car (and I've looked at most, if not all of them) sits in the middle-to-top area of the wheel housing, not the bottom. It might be easier to add these Ioniq air curtain ducts to your bumper cover while you have it off. At $6 per, it's a cheap, OEM-engineered solution that's pretty much guaranteed to work; all you have to figure out is how to get intake air to them.

Quote:

Originally Posted by freebeard (Post 570274)
What are the relative heights of the component parts?

Air curtains are for steerable wheels. Do you have rear-wheel steering? Else skirts.

The rear wheel 'curtain' as drawn is occluded by the side curtain anyway.

The 2018 Honda Clarity uses rear wheel air curtains.

http://ecomodder.com/forum/member-vm...219-163059.jpg

As they demonstrated with the original Insight, the public won't buy skirted cars.

kach22i 05-22-2018 03:26 AM

Quote:

Originally Posted by Vman455 (Post 570290)
Ioniq

Let's try that link again.

https://www.hyundaipartsdeal.com/par...nt-bumper.html

Other images.

Nosing ahead: Hyundai Ioniq Electric reviewed
18 October 2016
by Lem Bingley
Nosing ahead: Hyundai Ioniq Electric reviewed
https://3.bp.blogspot.com/-865ZFghmV...iq-ev-side.jpg

https://1.bp.blogspot.com/-3L0mZca7H...ir-curtain.jpg

Quote:

No doubt the Ioniq’s shape is aerodynamically efficient. Other, less obvious tweaks for the sake of efficiency include plastic inserts between the spokes of the alloy wheels, creating a smoother surface without much extra weight, and vertical slots in the front bumper that create an “air curtain” to help reduce turbulence from the spinning front wheel.
https://2.bp.blogspot.com/-p5i_CBAPI...ront-above.jpg

Vman455 05-22-2018 09:58 AM

Quote:

Originally Posted by kach22i (Post 570316)

Both links work on my computer.... One is for the RH duct, the other for the LH.

kach22i 05-22-2018 04:58 PM

Quote:

Originally Posted by Vman455 (Post 570328)
Both links work on my computer.... One is for the RH duct, the other for the LH.

Strange, both are working on my computer now as well.

The Ioniq example follows the larger opening, smaller exit rule, and looks to be a little higher than the center-line of the wheel as well.

mpg_numbers_guy 05-22-2018 10:19 PM

The rear wheel spats in the original picture look like they would increase the size of your wake by shooting air out the sides instead of directing it around.

hat_man 05-22-2018 10:32 PM

This idea sounds familiar. LoL.

http://ecomodder.com/forum/showthrea...hts-29302.html

freebeard 05-23-2018 12:56 AM

Quote:

Originally Posted by mpg_numbers_guy
The rear wheel spats in the original picture look like they would increase the size of your wake by shooting air out the sides instead of directing it around.

Properly shaped, a spat will force air down (like a wickerbill) to channel it toward the contact patch of the tire. Keeping it out of the wheel well. The side skirt could run out front inner front to outer rear, like a semi-trailer.

There is always a jet of air that squirts out either side of the tire right at the surface, where it is wedged together. Above that everything enters the ambient flow and is swept away. (Maybe a localized pressure increase. It's all about trading pressure and velocity.)

Squirting sideways would be like trying to hold your car door open at speed.

kach22i 05-23-2018 09:35 AM

Quote:

Originally Posted by freebeard (Post 570379)
Properly shaped, a spat will force air down (like a wickerbill) to channel it toward the contact patch of the tire. Keeping it out of the wheel well......................

Interesting I logged in this morning thinking that I should have mentioned wheel spats yesterday, but I would not have described their function in the terms you have.

I'm not saying you are wrong, just that I've never read this version before.

In my mind wheel spats offer no more or less surface area they are bluntly deflecting air from.

How they work is (according to what I can recall) they reduce the area of air hitting a spinning wheel, a spinning surface causes more drag and turbulence than a stationary one.

NOTE: some articles refer to rear wheel well covers as "wheel spats". That is not what I'm talking about.

Pictures and discussion of wheel spats in this old thread:

http://ecomodder.com/forum/showthrea...s-13669-3.html
http://www.davewigstone.com/uploads/IMG_0201.jpg
http://www.davewigstone.com/uploads/IMG_0203.jpg

freebeard 05-23-2018 11:15 AM

Quote:

I'm not saying you are wrong, just that I've never read this version before.
I don't know if I'd say it the same way (wickerbill) twice. It is true about the air that's ejected between the tire and the road.

kach22i 05-23-2018 12:43 PM

Quote:

Originally Posted by freebeard (Post 570406)
I don't know if I'd say it the same way (wickerbill) twice. It is true about the air that's ejected between the tire and the road.

No, no, I see what you were saying now that I've had time to think about it.

The rotating tire pulls or draws the air in the direction of rotation.

Meaning in the front of the tire air is moving downward, and at the rear of the tire the air is moving upward.

This is how we end up with vents at the top of wheel wells on race cars to release the pressurized air in the well accumulating at the top.

I just never micro analyzed the vortex leaving the wheel spat, and would like to see a CFD illustration of that one day.

freebeard 05-23-2018 02:29 PM

My favorite example:

http://ecomodder.com/forum/member-fr...4-hpim1176.jpg

(I know it's an open wheel)

aerohead 05-23-2018 03:53 PM

spinning wheel
 
Without the spat,the air is attacking the forward face of the tire at road velocity,while the forward face of the tire is descending vertically downwards at the same velocity.
Evidently,the chaos created by such a situation is worth some intervention.
With CFD,or a tunnel,the automaker can 'tune' a low-cost piece of thermo-formed plastic to divert the air in such a way as to optimize the interaction for the lowest drag,short of enclosing everything,which if done,would destroy the styling.

19bonestock88 05-23-2018 04:06 PM

1 Attachment(s)
So I got to work on this project some the other day, while my fenders were off... looking under the front bumper, I realized I didn’t have enough area to do an air dam like I drew... so I ended up with a basic lawn edging air dam in front and I ran out of material before I could make any side skirts, but I’ll likely buy some more lawn edging for the side skirts...

freebeard 05-23-2018 05:38 PM

Thanks for raising the topic.

Vman455 05-23-2018 06:40 PM

Quote:

Originally Posted by kach22i (Post 570395)
How they work is (according to what I can recall) they reduce the area of air hitting a spinning wheel, a spinning surface causes more drag and turbulence than a stationary one.

A few points from Aerodynamics of Road Vehicles:

-4.4.8.1: "...consequently the drag of a wheel rolling on the ground is lower than for a stationary wheel off the ground (see Section 13.42)."

-4.4.8.2: "As indicated in Fig. 4.12, the flow underneath a car spreads outward to the sides. Consequently the wheels are approached at an angle of yaw.... A yawing angle causes the drag of a wheel to increase; Fig. 4.75 gives a typical example. For a yawing angle of 15 degrees the wheel's drag coefficient is more than three times the value for zero yaw."

So, I think the function of these air dams we're seeing proliferating on cars today is not just blocking flow to the wheel face, but blocking flow in yaw to the wheel. That would explain why so many of them now curve around the inside face of the wheel, unlike just a few years ago when these dams tended to be situated slightly inboard of the wheel but with no curvature.

Old style (2018 Corolla):
http://ecomodder.com/forum/member-vm...219-153527.jpg

New style (2018 Prius):
http://ecomodder.com/forum/member-vm...219-152556.jpg

A more extreme example (2018 Cadillac CT6 plug-in):
http://ecomodder.com/forum/member-vm...219-145345.jpg

Might it be possible that these dams reduce the yaw angle of the flow on the inside face of the wheel, behind the rear edge of the dam itself? That might explain the cutout on the older generation of dam designs, something only seen now on a handful of cars (the Chrysler Pacifica hybrid being the most notable).

That section on wheel flow in Hucho also has a very helpful graphic visualizing airflow around a spinning wheel. Three pairs of vortices are shed from the wheel--two from the top, two from the bottom, two from the center--all spinning inward because of the rounded shoulders, and all raising the pressure behind the wheel due to entrainment.

freebeard 05-24-2018 12:53 AM

Quote:

That section on wheel flow in Hucho also has a very helpful graphic visualizing airflow around a spinning wheel. Three pairs of vortices are shed from the wheel--two from the top, two from the bottom, two from the center--all spinning inward because of the rounded shoulders, and all raising the pressure behind the wheel due to entrainment.
Can you provide a quote? In the picture at Permalink #15, you can see the front wheel's bottom vortexes passing the rear tire. The dirt carried over-top in the tread is well contained. I'd wondered about those streaks coming off from mid-wheel.

Another possibility on the spat is that it is to cover the tire when it is turned. Best practice in the rear is a fence right up against the inside of the tire.

http://ecomodder.com/forum/member-fr...bonnevette.jpg

kach22i 05-24-2018 06:03 AM

Quote:

Originally Posted by Vman455 (Post 570457)
-4.4.8.2: "As indicated in Fig. 4.12, the flow underneath a car spreads outward to the sides. Consequently the wheels are approached at an angle of yaw.... A yawing angle causes the drag of a wheel to increase; Fig. 4.75 gives a typical example. For a yawing angle of 15 degrees the wheel's drag coefficient is more than three times the value for zero yaw."

Wow, thanks - not what I expected at all, and not what I recall reading in the forum before.

As I visualize this, it would seem that the most effective spat would be one that not only covers the front of the wheel but the entire inside length.

That inside length or surface area is 2-4 times that of the width by my estimation.

For the front wheels the inside barrier (linear spat strip) would have to bow/curve and accommodate for steering arc.

Do we have a percentage of air escaping out the sides at 15 degree angle based on the amount originally entering under the front chin spoiler?

My truck has a chin spoiler that is lower than the sides, I assume that increases the amount or ratio of air escaping out of the sides.

On most cars the line of the lowest front barrier is near equal to the sides. That is our most common condition, right?

teoman 05-24-2018 01:49 PM

I am just starting to modify my car with skits.

The above descriptions are not fully clear in my mind.

How about an L shaped piece that covers the front of the wheel and the inner side?

The L shape does not need to go the entire length of the wheel well, it could be angled a bit to act as a deflector.

Vman455 05-24-2018 01:56 PM

Quote:

Originally Posted by kach22i (Post 570479)
As I visualize this, it would seem that the most effective spat would be one that not only covers the front of the wheel but the entire inside length.

They're certainly trending that way. Ford Focus, may it rest in peace:

http://ecomodder.com/forum/member-vm...101-161111.jpg

Has a tripartite dam that extends back almost to the centerpoint of the wheel. The C-Max has an identical dam, with the addition of a shaped fairing in front from 2014 on:

http://ecomodder.com/forum/member-vm...101-160936.jpg

Quote:

Originally Posted by freebeard (Post 570472)
Can you provide a quote? In the picture at Permalink #15, you can see the front wheel's bottom vortexes passing the rear tire. The dirt carried over-top in the tread is well contained. I'd wondered about those streaks coming off from mid-wheel.

Sorry for the crappy cellphone pic, I couldn't find it anywhere online:

http://ecomodder.com/forum/member-vm...524-124848.jpg

teoman 05-24-2018 02:55 PM

thanks, those pictures were helpful.

kach22i 05-25-2018 04:27 AM

Quote:

Originally Posted by Vman455 (Post 570513)
They're certainly trending that way. Ford Focus, may it rest in peace:

The two breaches, especially the one at the corner are odd.

I suppose if they made it continuous there would be more pressure on it.

I'd be tempted to seal those gaps up with some foil tape or rivet a thin strip of aluminum to it. I would not use screws, somehow it will end up in the tire with my luck lately. :mad:


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