Quote:
Originally Posted by Sven7
Thank you very much, Phil. My friend and I were thinking about testing his 1/4 scale clay model, and this information is very useful. I have a couple quick questions, though.
First, what size should the wind tunnel be? I imagine building one for a quarter scale model may be challenging if we can't find a dedicated space for it. Scaling that cardboard one up by a factor of six could take up an entire room. (The school has the space, but perhaps the CCS administration wouldn't appreciate that  ) We would probably have to make it out of MDF or some kind of particle board.
Second, and this one is for onefstek too, how does one make the smoke and get it in that neat stream? I've seen the needle like tools they use in the full scale tunnels but don't really know where they get them or what the smoke is from.
Edit: does anyone know how fast box fans run? Edit edit: 2-8mph. I assume to speed the air up to 40mph you'd need at least a 3x3 array of fans on the back end of the tunnel, with quite the funnel on the other end. Perhaps there's a better solution?
Blah, questions keep popping into my head. I suppose it's pointless unless one can't record drag, but how does one figure out the "fudge factor"? All the stuff I'd like to try is either over my head or beyond my resources!
Thanks! Tyler |
*If you do a closed test section,the models projected frontal area should be no more than 5% of the tunnels test section cross sectional area.This prevents the walls from effecting streamlines.
* I'm not current on smoke generator state of the art but in past times,an oil like SHELL Ondina was electrically heated within a metal wool,flashing off as a cloud of smoke into a vessel which was in series with the tunnel.Air from the tunnel enters the vessel at test section speed,picks up the smoke and enters the smoke wand or smoke rake,discharging into the section airstream at an equivalent velocity so as not to create its own turbulence.
*As of 1991, commercial smoke generators started at around $1,100 (US).
*Your fan(s) will need to develop a volume of air equal to your test section velocity (80-mph) multiplied by the section area ( 100 sq ft ),or,704,000 CFM.
*A local HVAC company could help you with static pressure requirements,friction losses and necessary horsepower to drive it all.
*And if you do measurements you'll need to construct a 3-component balance.Texas Tech used the 'sting' from a military aircraft.It has strain load cells of 3-axis.$68,000.
* Alan Pope has a fine book on low speed wind tunnel design.