In a message dated 9/27/2007 2:59:02 AM Eastern Daylight Time,
europa-list@matronics.com writes:
I'm wondering if a concentric lip projecting forward of the inlet...say
maybe as much as an inch (?)...could act in such a way as to divert
that vertically rising air around the inlet, reducing pressure in front
of the inlet, and increasing flow into your duct...? (I'm aware that
you've already tweaked the cowling geometry around the inlets.)
Hey Fred,
I tried using a thin mylar strip inside the intake hole to achieve exactly
what you mention and it had no effect. If anything it made it worse.
I think what is happening is a pressure wave is setting up in front of the
hole. It's caused by the spherical shape of the cowl intake and it's not at
all dissimilar to what happens when a smooth sphere is moved through a fluid.
Turbulating the flow on the edge of the sphere and the intake, much like
dimples on a golf ball, zigzag tape or vortex generators, should significantly
alter the airflow in a positive direction.
I've thought about dimpling the round parts of both intake areas like a golf
ball in lieu of the zigzag tape. That would make for an "interesting" look,
wouldn't it? It's tough to get the zigzag tape to lay flat in a curve like
that. I might wind up making the zigzag turbulator out of paint. I think I can
make a mold of sorts out of several layers of masking tape, then cut a ring
out with pinking shears, then shoot over it. The result should be the same
zigzag pattern, only made from paint. We've done this sort of thing before on
gliders, but never in a circle.
The real puzzle is why the right side doesn't exhibit the same flow
characteristics as the left. The right side sucks the string in with no
turbulation,
while the left side rejects the string on the outboard half of the intake
ring unless the flow is turbulated as the air approaches the intake hole. I've
placed the fan in such a way as to simulate the flow on the right side, but on
the left, i.e., fan blade rising relative to the hole, as opposed to
falling, and it made no difference. Granted, this is considerably lower flow
than
with the engine running at flight velocities, but I think the simulation should
be valid. I would think the pressure wave would only be stronger at higher
velocities. The flow behind the intakes above the top cowl, along the sides
of the cowl, and down the front of the cowl is very laminar, in fact a lot
more laminar than I expected. The only place I've seen the flow break is as it
gets to the junction of the windshield. I'm going to tuft that area in front
of the windshield on the top cowl prior to the next flight so I can see what
is going on there, too. There might be an advantage to be gained by a few well
placed vortex generators in that area.
Regards,
John Lawton
Whitwell, TN (TN89)
N245E - Grounded until Friday
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