Subject: [FlyRotary] New Scoop
Steve;
There are all kinds of things
one could say about trying to make the scoop ideal, effective, low drag, etc;
and then when you face the reality of fitting to your plane, you can’t do
it. So it’s what works for you. I’ll add a few comments for
whatever it’s worth.
The intake area of the scoop
should be fine.
One would like to slow (expand)
and turn the air entering the scoop in a manner that maintains surface
attachment for max pressure recovery and minimum drag. This takes a much
longer scoop throat than you have. The air entering will trip to
turbulent at the abrupt corner behind the B.L dam. This will result in
poor flow and pressure distribution, with most of the air going toward the
back of the scoop. I don’t know what happens in your installation
downstream from the actual scoop, but you might consider some internal baffles
but get a more uniform distribution if the rad is close to the
scoop.
The boundary layer dam that you
have is high drag, and may be close enough to the entrance lip that backup of
the B.L. flow will be ingested into the scoop – or it could result in some
external diffusion (pressure recovery) and allow the scoop to work just
fine. The idea in the B.L. “bleed” is to try to divert that flow
somewhere else, generally off to the sides. That would require a
much more gradual diverter angle.
I made a much more gradual bend
in the wall of my scoop (pic) attached. Still, in doing flow tests, I
found flow separation and turbulence which lead uneven flow
distribution. I added to baffles in the scoop get it fairly
uniform. It could be that some of the turbulence was a result of the
test rig setup, although I thought I had a long enough duct from the blower to
straighten things out.
The squared off internal corners
will add frictional drag, but probably not significant in overall
picture.
But, hey – try it. If it gives
you the cooling you need, you’ve got 90% of the battle won. If you feel
you need to reduce drag, you can consider that at your leisure.
Al