DIY wind tunnels

[AndyL]

Tow tank just requires a lot of length, recirculating tanks not as much...

Thankfully we have access to a couple 3d printers so models won't cost quite so much... making them not float away and getting some data however, could be more challenging in water...

I've found tons of NASA and *IT articles on water tanks, but most gloss over the dimensions, is there a frontal area to tank cross section or similar rule?

[aerohead]

Originally Posted by AndyL

Tow tank just requires a lot of length, recirculating tanks not as much...

Thankfully we have access to a couple 3d printers so models won't cost quite so much... making them not float away and getting some data however, could be more challenging in water...

I've found tons of NASA and *IT articles on water tanks, but most gloss over the dimensions, is there a frontal area to tank cross section or similar rule?

I never dove in deep on this technology,so I can't answer factually.I went the cardboard,duct tape,and tuft route,as it was really low budget in cost.
Since aerodynamics is a branch of fluid mechanics,my suspicion would be that everything is similar excepting wave drag on the sting,although you could do independent tests to evaluate the 'tare' drag of it.
And if you limit your measurement only to drag,you can cheat like hell on the 'sting.' Load-cell,spring tension/compression/pulley-weight system,all kinds of things could be done for force measurements.
I've only seen the Tech facility and the dimensions were enormous in proportion to the model size.I suspect that there was no guesswork involved with respect to its design.
I'll dig for that 1/24-scale article,perhaps there's some quanta in there worth looking at.
I'm off work all next week and can come here to do EcoModder during the heat of the day.I'll bring it.
It's a fun project that you're getting into,we should all learn a lot.

[AndyL]

Just trying to wrap my head around how to get real world numbers, from a small scale model... I'm no rocket scientist, that's for sure, but if I can work back to practical from the numbers...

Between the winter rebuild of my 5'er, a design I'd like to test (that '35 torpedo) and some questions about why the weekender teardrop tows consistently with lower MPG than the lower weight and smaller frontal area cub based teardrop that should be more aerodynamic...

[aerohead]

Originally Posted by AndyL

Just trying to wrap my head around how to get real world numbers, from a small scale model... I'm no rocket scientist, that's for sure, but if I can work back to practical from the numbers...

Between the winter rebuild of my 5'er, a design I'd like to test (that '35 torpedo) and some questions about why the weekender teardrop tows consistently with lower MPG than the lower weight and smaller frontal area cub based teardrop that should be more aerodynamic...

Do we have images of all those? I've never seen a teardrop trailer that was actually a 'teardrop'.
The highest mpg I've recorded with my truck was when pulling my gap-filled, full-boat-tail trailer.I was 1,300 lbs heavier than stock and recorded 22% better mpg than the best ever recorded without it.(47.9 vs 39 mpg).
Photos of your rigs would really help peel back the veil of mystery.

[AndyL]

Laptop is unavailable at the moment, but we can find representative pics...

My soon to be rebuilt rig, which will be a bit of a proof of concept for some building techniques


'35 torpedo


Since I can't access 'my' weekender (built it for a friend) pics: sample from tnttt forum

Plans at: http://www.mikenchell.com/images/mik...er-final-2.pdf


A cub based teardrop:

Plans I built from are here: http://www.angib.pwp.blueyonder.co.u...rop/tear31.htm

[aerohead]

Andy,thanks for photos.That will give me something to chew on.I can see room for improvement with everything,including the '35 Torpedo.
Problem is,compound curves,or at least generous edge radii would be required and plan taper if great mpg could ever be expected.I don't think most folks are ready for that.And it's the most challenging architecture to fabricate.Tons of man-hours!

[AndyL]

The 5ths rebuild will be all about curves, we have the technology, it'll be a light ply open web framework, composite shell built as a sandwich panel (SIP style) with an eye to taking every Aero advantage I can get (we do a lot of miles with it in tow)

The 35 torpedo - is somewhat where I want to go with the overall shape, but in a 5th setup... but it goes back to that truck to trailer interface - i m sure there's some improvement to be had there...

The weekender / cub - I've gone as far as swapping the frames, it doesn't make sense... the weekender with 5x10 sides, always pulls better than the cub (4x8 ply sides) - its been shown behind a wave, matrix, Tacoma, my full size with the truck camper on... its counter intuitive, the weekender is almost 300lbs heavier, has a bigger profile, but always gets better highway mileage...

[AndyL]

Here's what I'm pondering tank wise - 18x18x36" (maybe 48") test section, not sure on flow rate, need to come up with some target numbers for flow - that dictates a fair bit of the plumbing and design, in run and outflow - kinda like to be able to keep it on a 24x72" workbench, but we know how that works...

luckily the aquariums have me in ownership of some big pumps, got a few to choose from, up to a 6000gph monster, but they're not so speed adjustable, so guess a NEMA 17 steppers going to have to get adapted to a knife valve for flow rate control...

[aerohead]

Originally Posted by AndyL

Here's what I'm pondering tank wise - 18x18x36" (maybe 48") test section, not sure on flow rate, need to come up with some target numbers for flow - that dictates a fair bit of the plumbing and design, in run and outflow - kinda like to be able to keep it on a 24x72" workbench, but we know how that works...

luckily the aquariums have me in ownership of some big pumps, got a few to choose from, up to a 6000gph monster, but they're not so speed adjustable, so guess a NEMA 17 steppers going to have to get adapted to a knife valve for flow rate control...

Andy,I found what I was thinking about:
SAE Paper# 860091,"Aerodynamic Drag Studies on Rolling Vehicles by Underwater Tow Testing," by Mark L. Vorwaller and Geoff J. Germane,Brigham Young University.
They pulled a 9.5" long,and 2" tall model under 2-feet of water,in a 42-inch wide trough,at 11.761 mph.
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They also cite:
SAE Paper # 760189,"A Parametric Investigation of the Validity of 1/25 Scale Automobile Aerodynamic Testing," by M.E.Doberenz and B.P.Selberg.
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SAE is online and you could probably order the papers or facsimiles, or download them.They might save you a ton of time.

[ConnClark]

Originally Posted by AndyL

Ok so this is making me nutty... 2D simulators suck in real world applications

Who needs 2D? OpenFOAM, Blender, and Linux are free. You just need the determination to figure out how to use them. (I'm still learning but I'm starting to get realistic results).