Rusty;
I’m not sure I can be much help,
because the vagaries of airflow are many. Ultimately your going to have
to do some experimenting. I’d suggest that you need some more
information before you start building a new duct/diffuser. Ed’s
suggestion about getting a handle on whether there is enough airflow but poor
distribution is a good one; and Ernest suggestion of changing shape by some
simpler means is also good.
Figure out some way to get an idea of
flow distribution. If you are going to measure exit air temp to determine
delta T; you could get a rough idea of flow distribution by measuring exit temp
in 2 or 3 places - maybe divide the area roughly in thirds, and measure temp in
the center of each block.
Based on my scoop/diffuser shape, and
the flow tests I did, my conclusion about where the air is going is different
than Ed’s. My guess is that there is flow separation and lots of
turbulence at the front upper part of the duct, and most of the flow is
actually going through the core near the back end. It is also possible
that the turbulence, (resulting poor pressure recovery) and the sharp turn into
the core, may result in reduced inlet flow (air spilling around the scoop.
Your second version would probably
result in less flow separation, and better pressure recovery, but there could
still be issues of flow distribution and the need for some vanes. I had
more room for my scoop, and may have achieved something closer to a K&W
diffuser, but still had to install vanes to get a fairly uniform flow distribution
through the core. The air just didn’t want to make that turn.
See photos. But how the flow behaves in the diffuser is a function of the
pressure drop across the core, so your case is different.
FWIW,
Al
-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Russell Duffy
Sent: Saturday, October 23, 2004
4:57 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] oil scoop?
I'm still having some high oil
temps, though the cooler weather is allowing me to get by for now. I was
thinking of trying to apply some of the pressure recovery lessons that Ed tried
to teach us. It seemed to work pretty darned well with my radiator cores,
so I figure I should give it a shot for the oil cooler core as well.
Attached is a very crude drawing of
the cross section of my oil scoop. The top flat line is the evap core,
and the vertical line on the right side is the inlet. The top drawing is
the current inside shape of the scoop. As you can see, it isn't so
great. The bottom drawing is the proposed inside shape. Anyone want
to wager on whether this will help? As far as fiberglass goes, it would
be a fairly painless experiment. Think it's worth trying?
Rusty (Sir fiberglass hater)