Table-top Wind Tunnel

[FlyTiger77]

Has anyone built a table-top wind tunnel? If so, how well received were the activities you used it for?

I would like to see one used as the cornerstone of a program to rejuvenate AE in my group. Thoughts/ideas?

[JeffDG]

You gotta have some folks at TN-036 who know this stuff pretty well...

[coudano]

We messed with it at our squadron some years ago,
didn't have much luck getting any more wind speed off of the "tunnel" than we did directly off the fan(s)

It was fun trying, though (which is probably more what matters, as a squadron activity)

[SarDragon]

Check out the NASA Ames site. They used to have some good descriptions of the tunnels there, and the mechanics of how they work.

The two critical items in construction are the area ration between the inlet and the constricted section (more constriction is better), and the air volume. Small house fans won't hack it. You at least need one of the big floor fans they call "hurricane fans." Ity needs to be enclosed in the inlet duct. A flow straightener helps, too.

[Critical AOA]

As far as AE activities... that one kinda blows. 

[Huey Driver]

As far as AE activities... that one kinda blows.

We have cadet-built one at my squadron, and we use it in classes probably 3-4 times per year. We also will fire it up for a moment just to demonstrate some theories in the AE books.

There's a good amount of things you can do with it, like having the cadets design airfoils out of foam or whatnot, and (with a scale), measure the effectiveness and why, or gluing strings to the top surface to understand stalls and critical aoa, etc. Be crafty with it!

[FlyTiger77]

We have cadet-built one at my squadron..

I would be interested in seeing a picture or two of it if you care to share.

Check out the NASA Ames site. They used to have some good descriptions of the tunnels there, and the mechanics of how they work.

The two critical items in construction are the area ration between the inlet and the constricted section (more constriction is better), and the air volume. Small house fans won't hack it. You at least need one of the big floor fans they call "hurricane fans." Ity needs to be enclosed in the inlet duct. A flow straightener helps, too.

Thanks. I am looking for flow straightener ideas. I am going to try a ventilation fan from an old Army indoor rifle range--it may not move an adequate volume, but it is worth a shot as the price was right.

[SarDragon]

I can't find the olde articles on the tunnels, but as I recall, the straighteners were as long as one side of the duct entrance. For a table top system, half that might work.

Check out the Wikipedia article on wind tunnels. It has some good basic info, and a bunch of references.

[UH60guy]

Do drinking straws work as a cheap flow straightener? Can get a pack of 500 at WallyWorld for just a few bucks, and that's at least about 4-5 square inches of straight straws. Not sure if they add too much constriction though.

[a2capt]

I still want to build a back yard version for testing R/C aircraft designs.

I've got 3D foam cutters and a laser cutter. Now to test the outcomes

[MacGruff]

Do drinking straws work as a cheap flow straightener? Can get a pack of 500 at WallyWorld for just a few bucks, and that's at least about 4-5 square inches of straight straws. Not sure if they add too much constriction though.

Not really. But if you can get a plastic grid with rectangular holes in to that you can attach to the air intake, that would work.

[FlyTiger77]

Do drinking straws work as a cheap flow straightener? Can get a pack of 500 at WallyWorld for just a few bucks, and that's at least about 4-5 square inches of straight straws. Not sure if they add too much constriction though.

Not really. But if you can get a plastic grid with rectangular holes in to that you can attach to the air intake, that would work.

We were discussing using the rectangular grids used in some commercial indoor light fixtures cut to size and maybe doubled or tripled in thickness. I was also considering something like model rocket tubes, but it seems to me that it would be difficult to determine the optimum diameter (too large and it wouldn't straighten the flow where too small would impede the flow too much).

We are moving forward with it. It should be a fun project.

[jimmydeanno]

Do drinking straws work as a cheap flow straightener? Can get a pack of 500 at WallyWorld for just a few bucks, and that's at least about 4-5 square inches of straight straws. Not sure if they add too much constriction though.

Not really. But if you can get a plastic grid with rectangular holes in to that you can attach to the air intake, that would work.

A lot of people use the straw straighteners.  They're cheap, readily available, and will serve the purpose of a DIY wind tunnel.  I'd give it a shot, and make another lesson out of it if they don't work.

[BHartman007]

Perhaps you could cut pieces of PVC pipe? You can get in in several sizes and it's cheap.

I may try to design one. As an HVAC guy I have access to all sorts of stuff that would work for this.

[SarDragon]

Perhaps you could cut pieces of PVC pipe? You can get in in several sizes and it's cheap.

I may try to design one. As an HVAC guy I have access to all sorts of stuff that would work for this.

You would need to use the thin wall stuff to reduce drag. Round straighteners do add more surface area than rectangular ones. Look at pics of the big tunnels, and you'll see rectangles and squares.

What's the size of the inlet cross section? Fan size?

[a2capt]

Honeycomb aluminum like from a radiator.

[SarDragon]

Honeycomb aluminum like from a radiator.

Maybe, but if you make it long enough to do a good job of straightening, it might create too much drag. Radiators need surface area, the straightener, not so much.