Tuft testing

[Bill in Houston]

I have wondered that too. I mean, if I want plate numbers, I don't need to go look on the internet...

[CO ZX2]

Paranoia.

[lca13]

>>I would post the video, but I would have to block
>>out my number plate frame by frame ....

Post the video. You don't think people see your number plate when you are driving down the road? "-)

[Nerds laugh at me]

I'll post some stills. I notice even the magazines block out the plates.
There has to be a reason. ;-)

( Also the video is VERY shaky - almost useless really )

[Nerds laugh at me]

I uploaded some pictures at : http://www.flickr.com/photos/82006403@N00/

The tuft testing images are further down the bottom. There is atotal of maybe fifty or so.

[Bill in Houston]

Cool stuff. Thanks.

[lca13]

Very, very, very interesting..... partly because I hav a Civic, but still.....

Some observations, let me know your thoughts and between us all we might get some interesting conclusions.

- Kammbacl works on the side, but not the bottom (the bottom needs to be.... on the bottom. Where it is just introduces an additional voids and turbulence area

- Look at the back bumper.... flow down, under, and forward? Makes no sense if you think wind tunnel. Does make sense if you think about the car travelling down the road over stationary air, pulling some with it, leaving a vacuum to fill in from the sides, back, front, etc.

- Rear wheel well sicking in.... see previous

- Front wheel well not sucking in.... maybe that really is brake dust on the front rims :-)

- Serious cowling into hood flow... bet the vent works well

- Texan eh? Not an Aggie I hope.

- Something you have good that I did not... no flow into the front hood seams. I had to beef up the weather stripping there.

- Interesting that you have a belly pan,,, and also the rear bumper reverse flow... thinking it would be worse without the pan, or the pan did something unexpected.

- Yeah, my mirror sux too

Wow... thx for the shots.... very enlightening. Gives me some clear ideas on changes.

[MetroMPG]

Originally Posted by lca13

- Serious cowling into hood flow... bet the vent works well

No kidding!

Great photos. Very instructive.

[Bill in Houston]

Originally Posted by lca13

- Look at the back bumper.... flow down, under, and forward? Makes no sense if you think wind tunnel. Does make sense if you think about the car travelling down the road over stationary air, pulling some with it, leaving a vacuum to fill in from the sides, back, front, etc.

That IS weird... So much flow downward at the bottom edge of the bumper, and even FORWARD at the end of the bumper. That can't be good... I wonder if fences behind the rear wheels would keep that from happening...

[lca13]

This is one of those counter intuitive things. I think it helps to not think wind tunnel and think staionary air with car moving through it. The air under the car for example, on one hand gets battered around with a net forward momentum add. Contrasting this is the air up front which is rushing below and under the bumper picking up speed towards the rear. Messing it all up even further is the stuff exiting the engine compartment. So you likely end up with a pressure increase under the car up front, and a decrease near the rear. Note that the data in these pictures has me thinking of this explanation, not independently, but this explanation would describe the observed behavior.

If all this is correct, the following should help (let's see if the recommendations are consistent with other observations):

- Less air into the engine compartment means less backward velocity increase and turbulence underneath..... grill block.

- Smoothing out the underbody imparts less forward momentum into the stationary air..... underbelly pan.

- Deflectors underneath diverting air around remaining appenditures, like lower control arms would help in addition (but should be teardrop shaped completely.... just a parabolic front is not enough.

- Deflectors in front of the front wheels to divert air outward would help.

- Wheel skirts (exterior) in the back to keep air from rushing into the rear vaccuum would help.

- Wheel skirts (interior) in the front would keep the flow underneath the car

- Vertical lengthwise channels would keep air flow uniform and.... but here is an anomoly... a diffuser to reduce velocity in the back would be counter to the data.... want to speed up in this case?

- Any spoiler up front that moves air up instead of down should help (smoother streamlining above).

- Lowering the car should help.

This is starting to make sense :-)

For the coup de gras, a properly channeled underbody with an electric fan assist in the rear, velocity driven by delta air pressures between the under rear and the behind.... equalize ????