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Subject: [FlyRotary] Re: K&W Streamline duct vs 7 deg optimum duct
> What would result if you used a 7 degree side wall duct with the K&W
curve
> at the core end?
>
> Joe Berki
> Limo EZ
Good question, Joe. I honestly don't have a clue. The key (according to
K&W)
appears to be having the side wall diverge just enough so that the pressure
increase along the wall (caused by friction slowing the airstream) is
matched by the centrifugal force of the air flowing around the curve of the
wall.
Its not that you don't want a pressure increase, you do, but apparently you
want it as close to the face of the core as you can get it. This appears to
minimize disturbance of the air flow closer to the inlet where it would
affect the more/(the entire) air flow. I would guess that any duct you use
that approximates the coordinates of either the 7 Deg duct or the streamline
duct would be better than one that does not.
Note on the attached diagram from K&W that the more convential diffuser
shape shown on the same diagram has a big pressure drop at x/YB = -1.5
coordinate point. Note that there is very little difference in the two duct
curves at that point. However, the difference (the traditional diffuser is
smaller there) appears to cause a ventura effect (speeding up the air flow
and causing the pressure to drop quite a bit at that point). Pressure
recover does occur shortly thereafter, but the total pressure recovery is
less than 1/2 of that compared to the streamline duct recovery.
Ed Anderson
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