DIY flow visualisation.

[asdf]

Hey everyone.

I'm doing a project in school in a month or so (gathering ideas) and I'm thinking of doing some kind of DIY flow visualisation rig/small scale wind tunnel that works (to an extent).

I'm wondering about ways to visualise (Microsoft, that's how you spell visualise, deal with it.) flow. I'm guessing evaporating dry ice in water and piping into the inlet of a fan could work. Wool tufts could be an option too.

Many of you guys seem to have a higher IQ than myself, so please help me with this.

Thanks in advance.

[Dragonfly]

I am far from aerodynamics and just very curious what answers you get here from the more educated people.
But I think smoke/vapor generation aside you'll have to condition the air stream in some way to eliminate to some extent the initial vortex by the fan to be able to get a representable picture of the flow around an object.

[asdf]

I am far from aerodynamics and just very curious what answers you get here from the more educated people.
But I think smoke/vapor generation aside you'll have to condition the air stream in some way to eliminate to some extent the initial vortex by the fan to be able to get a representable picture of the flow around an object.

Yeah, forgot about that detail. Maybe a movable(up and down) small I.D. tube/hose could be used with a right hand kink. Drag of the tube would be somewhat irrelevant as this isn't about getting results, more so a demonstration of how something works.

Thanks for your help and anyone else who decides to chime in.

[simieski]

Depending upon the scale of the experiment, the use of drinking straws immediately after the fan would help create a relatively laminar flow.

A couple of examples:
http://homeikea.blogspot.co.uk/2012/03/ ... -soda.html
http://softsolder.com/2010/12/10/simple ... mple-fans/

[astracrazy]

some ideas here

http://www.rcgroups.com/forums/showthread.php?t=27538

stick homemade windtunnel in youtube and see other peoples designs too

[asdf]

Depending upon the scale of the experiment, the use of drinking straws immediately after the fan would help create a relatively laminar flow.

A couple of examples:
http://homeikea.blogspot.co.uk/2012/03/ ... -soda.html
http://softsolder.com/2010/12/10/simple ... mple-fans/

Year 7 Science project. Something tells me that this isn't going to have much practical use, so KISS (as in the principle.)

Thanks to everyone so far.

EDIT: Anyone got ideas for flow visualisation? Must be relatively cheap and easy to get in Australia.

[skgoa]

A couple of ideas:

- If you don't care about the extend to which your results can be applicable to reality, water flowing at relatively small velocities is excelent for this. (I know model plane people who use water tanks in lieu of actual wind tunnels.) You can use ink or just coloured water - e.g. applied via a syringe - to mark whatever flow you want to visualise.

- Bits of tape or little strings of thread have been used to great effect in the past. Either attach them to whatever body you want the flow to interact with or put an entire "field" of those little markers behind the object. The latter is a very easy trick to show wing tip vortices.

- As has been touched apon, any kind of wind tunnel will be much more than the "test area". I.e. you will need quite a good pump and big pipes. Then a diffusor (basicly a widening part of the tube) that is of the correct size to slow the flow down exactly the right amount. Then a surprisingly long "straightening chamber"; the links that have been posted are a good start but my gut says you will have to double the length and use a lot more straws to get all the turbulence out. And then, finally, the test chamber. If you want to recirculate the air, it gets even more complicated.

- Laminar flow without vorticity is nice to have in a wind tunnel (hence going to all the trouble mentioned above) but it's not the only interesting flow. You could inject drops/streams of ink into jars of fluids that have different viscocity and show that they behave differently. Or you could show how tea leaves move towards the center in a spinning cup.

edit:
- Or just look up a recipe for flo-viz dye and put that on whatever opjekt you want to test. Then put a big and/or strong fan in front and look at where the dye is being moved and how it is moving.

[Richard]

Put the fan at the exit to pull the air to reduce turbulence.

You could get some quantitative data by making your own pressure taps to measure pressure gradient over the surface. You just need some thin tubing and a manometer. It'll be crude but you should be able to demonstrate there is a pressure difference between the top and bottom surfaces of the object.

[ffangio]

It depends on what you want to look at.
Wool tufts are ok for seeing whether flow is attached or not.
Smoke / dry ice will give you a vague idea of where flow is going but is not much use for anything more.
Oil coloured with paint powder is great for surface flow visualisation, much better than water. Just mix together some fine oil like mineral oil or gearbox oil with the paint powder and paint on a thin layer to the surface.