Ed
wrote:
If a "full-strength" Streamline duct were tested under
the conditions of
9.5"H20 at the entranced to the inlet then at the
widest part of the duct
you should theoretically measure 9.5*.84 =
7.98". I recall Tracy Crook
getting 5.6" at 120 MPH in front of his core -
certainly he had a different
configuration, but just a data point. So your
3+" H20 is certainly a bit on
the low side. So what could cause that? I
see three possible causes:
1. Duct not properly shaped (but, based on your
sketch it looks fine to me)
It is attempt to
follow the K&W diffuser shape; but is truncated to fit the short distance
available. Perhaps that plus the turn . . .
2. Exit area insufficient (you don't mention the
ratio of inlet to exit
area) –
The ratio is about
1.6 : 1.
3. Boundary layer ingestion. With no
standoff from fuselage for you inlet,
it is possible (likely?) that a percentage of your air
into the duct could
be composed of the boundary layer.
The BL is being
ingested; no doubt about that. The ram pressure I measured at ½” from
the under-wing surface suggests to me that there is not much of a boundary
layer effect; IOW the 9 ½” H2O represents roughly the average velocity into
the scoop – which extends to 1 ¼” below the surface. It could well be
that the BL along the surface exacerbates the flow separation/turbulence in
the duct.
I’m wondering about
a vane in the scoop – roughly as show in the attached
drawing.
The experts on the
other list are suggesting the second sketch (attached).
Al