Re: [Phys-l] Wind generator output versus wind speed.

[John Denker <jsd@av8n.com>]

On 04/06/2008 10:18 AM, Rick Tarara wrote:

>  One factor that comes to mind here is that our fans 
> (straight from Wall-Mart) have a fairly narrow stream of air.  I think I am 
> completely 'painting' the rotor blades with the air--adjusting the 
> orientation of the fan for maximum power output. 

If you're going to be doing fluid dynamics experiments, you need to
build a diffuser box:
  http://www.av8n.com/physics/img48/diffuser.png

That is, get every kid in the class to bring in the cardboard tube
from the core of a roll of paper towels.  Stack the tubes in a
honeycomb lattice at the end of a box.  Put the fan at the other
end of the box.  The fan builds up a tiny pressure in the box, and
then the air flows out the tube.  The friction in the tubes makes
the outgoing flow vastly more uniform and less turbulent.  

The undiffused blast from a fan will drive you crazy.  There's no
way to make anything approaching a quantitative measurement with it.

> operates with a fixed 100 ohm load (so that the 
> software will work). 

I'd recommend getting rid of the fixed 100 ohm load; otherwise any
notion of optimality is dead on arrival.  If the software is really 
wedded to a 100 ohm load, then get rid of the software as well.  
For the amount of data we're talking about, taking I and V readings
by hand is a negligible part of the overall effort.