Small scale wind tunnels

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Formula None
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Joined: 17 Nov 2010, 05:23

Small scale wind tunnels

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Great post by Mike over at Mulsanne's Corner regarding IMSA car designer Yoshi Suzuka's development of an "office sized" wind tunnel for small scale aerodynamic testing.
Long time readers of Mulsanne's Corner will be familiar with Yoshi Suzuka. As you'll recall, Mr. Suzuka was responsible for the aerodynamics of Nissan IMSA GTP race cars that dominated IMSA GTP in the 1980s & 90s.

These days Yoshi is enjoying his retirement. But he isn't sitting still. Yoshi has been working on a Office Size scale wind tunnel. Yes, it's about the size of a small cat carrier and accepts 1/24 scale models, and it will even measure front and rear lift forces as well as drag.

Now some people are going to immediately scoff at this. But watch the videos, Yoshi has made a 5 part video series that shows the model functioning and him working through a test case. Understand that Yoshi doesn't make any claims that the data is accurate to full scale, simply that the trends are accurate. Yoshi used 1/7 scale models for the Nissan IMSA GTP program and designed and built NPTi's wind tunnel. According to Suzuka, he was able to achieve 2% and 4%, drag and downforce respectively, correlation to full scale with this tiny windtunnel. This being the closest correlation to full scale in any of the 14 wind tunnels he used throughout his 35+ year career. And the Nissan GTP program achieved results, so Suzuka must know a thing or two about what he's up to with his Office Size wind tunnel.
http://www.mulsannescorner.com/newsmarch11.html (post date 4/26/11)

I was glued to these videos for like half an hour:

[youtube]http://www.youtube.com/watch?v=mpMOpyLb ... re=related[/youtube]

[youtube]http://www.youtube.com/watch?v=E1IIMFOF ... re=related[/youtube]

[youtube]http://www.youtube.com/watch?v=Ww29IAN6 ... re=related[/youtube]

[youtube]http://www.youtube.com/watch?v=DpzRPfd9 ... re=related[/youtube]

[youtube]http://www.youtube.com/watch?v=EYmsFAGX ... re=related[/youtube]

Yoshi's website: http://www.suzukaracing.com/

I love stuff like this, it looks like so much fun. I believe he mentioned 0.5% repeatability in the videos above. I see no signs of him selling this desktop unit anytime soon, so we should create some plans ourselves! I'm sure many of you guys could offer suggestions for appropriate AC motors and controllers, fans, load cells, affordable linear slides, etc.

Rough BOM off the top of my head:
  • Flat, rigid, lightweight base
  • AC motor & controller
  • Fan
  • Ducting
  • Load cells (2 for downforce/lift at each axle, 1 for drag) & readouts
  • Load cell carrier mounted to linear slide for drag measurement
I'm pretty sure I've seen plans for DIY wind tunnels online before, so if you know of any good ones please feel free to comment.

Also, it might be good to discuss the following:
  • the merits of open & closed wind tunnel designs
  • the necessity of a rolling road & simpler/cheaper ways to achieve a similar effect (boundary layer suction?)
  • water tunnels vs wind tunnels for small scale models (tunnel design simplicity & operating cost vs reynolds numbers)

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flynfrog
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Re: Small scale wind tunnels

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Ive been trying to get one of the f1 in schools kids to do this

Formula None
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Joined: 17 Nov 2010, 05:23

Re: Small scale wind tunnels

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It would be great for that & RC cars & whatnot. No concern for the effect of the model's scale & reduced Reynolds number.

The creator mentioned in the videos he was intending its use for small, low budget race teams to compare small model iterations, & for aftermarket equipment manufacturers. Maybe its worth it, maybe not. The fact that we don't see much small scale wind tunnel work being done may imply that there's not much value in it. I don't know. You have to consider though how much aerospace development has been done over the years with scale models.

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Jeffsvilleusa
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Re: Small scale wind tunnels

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brilliant!
Box! Box!

beelsebob
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Joined: 23 Mar 2011, 15:49
Location: Cupertino, California

Re: Small scale wind tunnels

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Formula None wrote:It would be great for that & RC cars & whatnot. No concern for the effect of the model's scale & reduced Reynolds number.

The creator mentioned in the videos he was intending its use for small, low budget race teams to compare small model iterations, & for aftermarket equipment manufacturers. Maybe its worth it, maybe not. The fact that we don't see much small scale wind tunnel work being done may imply that there's not much value in it. I don't know. You have to consider though how much aerospace development has been done over the years with scale models.
Or simply that no one has been clever enough to design a useful one yet.

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Ciro Pabón
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Joined: 11 May 2005, 00:31

Re: Small scale wind tunnels

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Well, no baffle. Or is there one?
Ciro

Formula None
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Joined: 17 Nov 2010, 05:23

Re: Small scale wind tunnels

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There seems to be a honeycomb screen downstream from the fan, acting as a flow straightener.

I think the hardest part to source would be a small motor that spins fast enough, & finding a fan that size (6" dia?) that designed to work in 60mph+ velocity airflow. Are these by any means standard parts used for some other purpose?

Maybe a larger motor with a belt drive would be a compromise. Also, a big centrifugal fan with a tapered nozzle to ramp up airspeed might be another option instead of looking for an small, efficient axial fan. But then you start to lose the whole "desktop wind tunnel" appeal.

ESPImperium
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Re: Small scale wind tunnels

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Ive seen some school physics labs having something simmilar, but less technologically savvy. One was at my old high school and the other was at another high school i was using one year for extra Maths classes.

For a honeycomb they used a big bunch of straws for a flow conditioner down stream of the fan.

The fan was a bunch of small computer fans, one i saw had 4 smaller fans, one other had a pair of large fans. Theese were controled by a couple of 500K potentiometers varing the voltage.

Not sure how they came about getting a smoke flow from them however.

The old one that was for the Advanced Higher physics module at my school was a cobbled together one, sort of a mixture of a Craft class project and a Science project that is kind of made to look like a homework project.

The only limitation to the fans was the fact they were so small, effectivly they had to make the models smaller than what the "tunnel" should take simply to get the desired wind speed. I think the wind speed was ment to be at 45KPh at 1:1, but they needed to get to 90KPh, so dropped the models to 1:2 scale just to get the speed up to 90KPh, all things being constant. Not even a increas in voltage could make the motor spin faster, simply because the motors would burn out after a few uses.

Consept could be done, and for small teams, if this was avalable for a small (relitivly) ammount of money, i thinlk the takeup would be quite good of people buying them.

One thing id like to do is put a coouple of Minichamps models of mines thrugh one, would be intresting.

Caito
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Joined: 16 Jun 2009, 05:30
Location: Switzerland

Re: Small scale wind tunnels

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Formula None wrote:There seems to be a honeycomb screen downstream from the fan, acting as a flow straightener.

I think the hardest part to source would be a small motor that spins fast enough, & finding a fan that size (6" dia?) that designed to work in 60mph+ velocity airflow. Are these by any means standard parts used for some other purpose?
RC motors, not electric though. Are REALLY powerful. I have .25cubic inch(4,1ml) engine.

Its supported in a wood which weights 10kg, and the engine max throttle moves the wood through the floor.

These produce very very higgh speeds. RPM can exceed 15k and are not very expensive, simple and reliable. Noisy though. A similar powered brushless engine(again, for RC) would cost much more, plus batteries, plus they last no longer than 10 minutes.


Here's an example:

Displacement: 0.248 cu in (4.07 cc)
Bore: 0.709 in (18.0 mm)
Stroke: 0.630 in (16.0 mm)
Practical rpm range: 2,500-16,000
Power output: 0.75 ps @ 13,500 rpm
Engine weight: 9.7 oz (275 g)


I have an engine, but I don't know how to test the wind speed.
Come back 747, we miss you!!

Formula None
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Joined: 17 Nov 2010, 05:23

Re: Small scale wind tunnels

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I like the RC electric motor suggestion, Caito.

Something like this might also be an affordable option:

Image
http://www.mcmaster.com/#duct-fans/=c4x928 (3 or 4 feeding into a funnel)

As far as load cells go, there's a lot out there. For our purposes it needs to operate in compression and tension, so both lift & downforce can be measured.

Trouble is, cells that can do that(parallelogram or s-beam type) are pretty pricey (I've seen minimum $400, and this wind tunnel needs at least three of them).

http://www.futek.com/product.aspx?stock=FSH02664
http://www.futek.com/product.aspx?stock=FSH00011

You could get a pretty accurate digital scale and scavenge the load cell from it. Trouble is, I'm not sure if you could modify it to read in tension & find a readout that would also be compatible. Any ideas?

http://www.amazon.com/Digital-PENNYWEIG ... 866&sr=8-6

(^ 600g cap.; resolution: 0.1 g)

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amouzouris
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Joined: 14 Feb 2011, 20:21

Re: Small scale wind tunnels

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Where did you buy your load cells from and what type of load cells they are? I would really like to know please [-o< [-o< [-o<

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mep
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Joined: 11 Oct 2003, 15:48
Location: Germany

Re: Small scale wind tunnels

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I really like your idea to make our own wind tunnel. When I was a child I took a hair dryer to blow a Ferrari model until the plastic got soft by the heat.
In theory its no big deal to build a wind channel. Just the results will be far of but anyway I think a lot can be learnt by it so it’s worth a try.
Formula None wrote: As far as load cells go, there's a lot out there. For our purposes it needs to operate in compression and tension, so both lift & downforce can be measured.

Trouble is, cells that can do that(parallelogram or s-beam type) are pretty pricey (I've seen minimum $400, and this wind tunnel needs at least three of them).

You could get a pretty accurate digital scale and scavenge the load cell from it. Trouble is, I'm not sure if you could modify it to read in tension & find a readout that would also be compatible. Any ideas?
You don't need a load cell that can read out tension.
You just preload a compression cell and set zero.
For example if you have a cell that can measure from 0-600g in compression you put a weight of 300g on it and set zero to that position. By this you get a cell that reads from -300g to +300g. So in principle a kitchen scale can do the job but it would be more practical if you can buy the cells of the shelf. For the drag cell you might use a small spring to preload it but possible it is not even necessary. The spring you could take from a ball point pen.



You might also thing about ways to make airflow visible. This guy used some strings but I would use some proper smoke because the stiffness of the strings might affect the results especially on such a small scale. During my studies I already got some experience with this stuff:

http://www.bjornax.se/Default.aspx?lang ... %26cat%3D6

Coloured smoke is better visible than white one. So you should go for that. I took the powder out of the cartridges and let it go trough a tube to adjust the amount of smoke. You will need to make videos of the test because you have to handle a lot of stuff during the same time and can hardly watch what actually happens.

I also used a stroboscope lamp for the videos. It makes the flow easier to spot and you need some light source anyway. You can see some really fascinating things with such a lamp like the flow out of a water-tap.
http://en.wikipedia.org/wiki/Stroboscope


Very important is also to know the exact airspeed. You will need some measurement device to find that out. I had this one:
http://www.kestrelmeters.com/Kestrel-20 ... -meter.pro
It did his job but the impellers didn’t like the high air speeds we had so they failed after some time. Maybe there is something more fitting device around.
Regarding the motor/ fan.
I would definitely not use any petrol engine. I think the simplest way is to use some DC engine from your local model maker shop you also get the fitting propeller there. You prolly should take a cheap engine. It will do the job anyway and we will not handle it with much care. The electric current you can get from a laboratory AC/DC power supply. Something like this. Sorry that the link is in german. I couldn’t find a better one. It’s just to show you what I mean. Maybe you already have one of these at home or know somebody who has one.

http://www.conrad.de/ce/ProductDetail.h ... 3524766720


Important is to get the vortices out of the airflow. The idea with the honeycomb is really good. I just wonder how long the calm down distance has to be. I would say at least 10cm but better even more like 20cm.

Caito
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Joined: 16 Jun 2009, 05:30
Location: Switzerland

Re: Small scale wind tunnels

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A simple pitot with a pressure gauge can measure wind speed too. Or any hot wire anemometer. They're not very expensive.


Summing up:

Ducted fan RC motors. Fed with a power source(obviously you don't need a battery, I was thinking planes :p).

One can buy two scales and put them front and rear, or just one, to begin with.
Oh, and drag, let's suppose we use a simple spring and measure its length.

You get something to measure wind speed, and then?

What do you do with air flow, do you enclose the thing? As with real wind tunnels and giant venturis?
Come back 747, we miss you!!

marcush.
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Joined: 09 Mar 2004, 16:55

Re: Small scale wind tunnels

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you can use modern Automotive axial fans for this .There are 300 to 1000W fans available with integrated electronics (PWM) so you got almost full control over the rpm ,of course you need to baseline ..as the tolerance from the fan alone is staggerring even for a EC setup.
Currently not many Companies use a 1000W setup -which is only available from Brose -for Volkwagen .Brose supplies two lines of EC Drives to the automotive industry and those are available with 850W in cars like Panamera turbo (ex Conti/temic)and Cayenne/Touareg(Brose -ex Siemens).These drives are developped for moving air and with minor wiring and electronics you get a reliable source of air including fanblade and shroud for moderate money
alternatively EBM papst has a wide range of products as well available ,catalogue and online...

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