Who uses encyclopedias nowadays? I do, for making a lousy wind tunnel.
It might be lousy, but it greatly reduces the noise in my measurement. Top graph is from a fan in front of the tempest about 1m distance without my wind tunnel, bottom graph is with the wind tunnel. I’m happy (except for the result, which I’m discussing in another thread).
Is it possible that the short sample time of the Tempest picks up the wind pulse from each fan blade and that the tunnel tends to smooth out the pulses?
Ideally, you would have a series of small tubes, like straws, all stacked together across the tunnel opening to create laminar flow in the tunnel. A wind tunnel I saw several years ago at a science teacher’s convention had the fan on the exit side and straws across the inlet. This created a great laminar flow without any rotation or turbulence in the air stream caused by the rotating fan.
Surely that is possible, and with my other fan you could even feel that the power wasn’t constant. With my previous wind tunnel I did add some stripes to make it more laminar.
But non-constant laminar flow would still be causing extra noise. This fan is more stable but certainly not perfect.
However, for my experiment itself it didn’t matter. Basically I did the experiments in the wind tunnel first, but then I remembered that David at some point warned me for reflection of the ultra sound inside the tunnel that might cause some weird effects. That’s why I measured my problem also without a wind tunnel. The result of having less noise when using a tunnel was just an added bonus.
get a great big drainpipe not books…them’s supposed to be cylindrical, then you would have no seams and more accuracy. so as to match the shape of the source (fan in this case)
You said it not so lousy
wind tunnels don’t have to be cylindrical (I’m guessing most of them are not). All you want is a constant laminar flow in an area that is relatively large compared to the object you are measuring the wind effect on. I could make numerous improvements and my first version from a long time ago was much better than this lousy one. However it doesn’t need to be better for the effects I was trying to measure. The book version is more than good enough.