DIY full size wind tunnel

[Vekke]

Answer was already there. Miniature full size truck is 100mmx150mm=15000mm2=0.015m2
with that 5% rule I get cross sectional area of 300000mm2=0.3m2=3.3 square feet.

In cross sectional dimensions this means 450mmx665mm

That was good tip to make that tunnel portable. There is only one problem you should be able to put that car you are measuring on the side of your car. Otherwise your cars aerodynamics would influence to the cars you are measuring?

Can then some verify that same cross sectional rules apply to water tunnels?

[NeilBlanchard]

Thanks for posting to this thread -- I'm building a 1/4 scale model of CarBEN and I'd like to build a wind tunnel to tuft test it. The model is 41" long at it's longest points, and 16 1/2" W x 16 1/2" H -- does this need to be 38 sq ft opening? That's a little more than 6' x 6' ... and then how long would it need to be?

[Vekke]

Originally Posted by aerohead

justpassntime,is there some specific info your seeking? I know you're aware of Reynold's Number effects, and how it effects model scaling in wind tunnels.A 1:24 Scale model would require a minimum of 480-mph wind in the test section to just simulate a turbulent boundary layer on your model .Anything short of that would yield meaningless data for you.If there's something specific you'd like to know about your car or potential projects,we may be able to help you out.I have a small tunnel I built for public demos but it's not a serious research tool.And for me,I can intuit and tuft-test in full-scale,faster and cheaper than I ever could with models.And the results are always valid 'cause its full-scale.Let us know.
.

From other topic aerohead has pointed out that the wind speed needs to be quite fast 480 MPH on smaller scale 1:24 models :/. That sounds like a small problem

[Vekke]

Originally Posted by aerohead

Typically,you need 6-pipe diameters length of tunnel to kill vorticity and get nice even laminar flow into the test section.If yo do circulation,you can save on power but you have to do alot of full area turning-vanes at every corner and then maybe flow-straighteners before the test section.

There is the answer so 6x width of the tunnel?

[Vekke]

Originally Posted by aerohead

A spray booth would make a great test section.They are smooth-walled and have recessed lighting.Frontal area of model would be limited to 5% of test-section area,so size of booth would determine maximum size of model.Remember,without a turbulent boundary layer your results would be garbage.In full-scale you need at least a 20-mph air velocity for proper Reynold's Number.At 50% you'd need 40 mph.25% -80-mph,and so on.Pope has a great book on" low-speed wind tunnel design."It's worth checking out.The re-circulating design is cheapest to operate,although if using smoke you've got to design for that.

Again from other topic: on your 1:4 tunnel you need 80 mph wind speed .

[Cd]

I have a knucklehead idea that borders on the ridiculous, but here goes :
If you want to test a scale model of a car with a true 65 -70 MPH windspeed, you could test it in the bed of a truck mounted high to avoid the turbulence from the cab.

Sorry if that has been mentioned before I didn't read everything here.

[NeilBlanchard]

I'm not looking for a Cd number; all I want to do is tuft test and find the problem areas, so the proper velocity is not critical.

[KamperBob]

Originally Posted by NeilBlanchard

I'm not looking for a Cd number; all I want to do is tuft test and find the problem areas, so the proper velocity is not critical.

Neil, obviously a wind tunnel is for understanding full field flow, but I wonder if you might get any insight by testing specific regions with a leaf blower...

[AeroModder]

You mean like this?

http://www.youtube.com/watch?v=HPG6Z_a_hLo

[Rokeby]

A very interesting topic for thought experiments. I suppose almost everyone
who has even a moderate interest in vehicle aerodynamics harbors a secret
desire to build a backyard wind tunnel.

Of all the possible configurations, my musings have settled on an open air
arrangement. Perhaps it's overly simplistic, but I have been thinking:
* Get a piece of level land in an area that is frequently very windy
(*See refs below.)
* Ensure that there is a clear path upwind; no trees, buildings. etc.
* Install a ground-level turntable (~ 20 ft diameter?) to point car upwind.
* Have rollers so powered wheels can drive un-powered wheels to wind
speed.
* Do smoke/tuft tests to your hearts content including wind off-center line.

It seems like all the height, width, and length issues would not apply.

With luck, if you built it ,""they would come."

Of course some accomodtions would have to be made for non-windy days/nights.

* Windy US places refs:
Wind Energy Resource Atlas of the United States, Map
Wind Energy Resource Atlas of the United States, Text Descriptions
Top 10 US Cities Weather Facts and Extremes