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Since Marv may be looking, I am sending the
attachments to his e mail in two parts.
The first attachment is Flow
Sepearation01.jpg and is attached to his e mail. The second and third
attachment are Boundary Layer Growth in Nozzle Diffuser.jpg and Converging
Diverging Duct.jpg sent by themselves in a second e mail. Part II of
II
Since I know I am not likely to produce any book on
cooling any time in the near future, I thought I would pull together the essence
of one small area where I do believe I may have come up with something useful
related to cooling. You, can then ,of course, come up with your own
interpretation of the same material I made use of.
The first attachment, is an extract from a NACA technical
document - the identification of the complete report is NACA-WR-L-208.pdf
originally issued in June 1944 with a WarTime security Classification
entitled "Design of Power Plant Installations - pressure-Loss Characteristics of
duct Components"). You may be able to find the complete report on the
web.
I extracted the first page and a half as that
really summaries the findings of the study.
I underlined in blue the material that
eventually led me to come us with the idea of "Pinched Ducts"
and to fabricate them. Didn't happen the first time I read this
though.
I somewhat later found the slide (in the material on
Flow Separation) entitled "Boundary Layer Growth in Nozzle
Diffuser." Note the last factor in the first column of
this slide and then refer back to the abstract material. All this was neat
but the idea had still not yet blossomed forth. Then when I happened to
see the drawing of the converging/diverging nozzles, I think it pretty much all
fell into place.
When that light bulb came on I then went back to the
streamline duct of K&W and understood why the long straight tube for
maintaining a higher air velocity (less separation) and then the sudden flare to
the bell shape for pressure recovery worked so well. The StreamLine duct
seems to pretty much jive with the findings of this NACA study... in
my opinion.
Again, I repeat, I do not believe
the "pinched duct" is as effective as a full up Streamline duct, but I do
believe it results in less drag (and perhaps nearly as good pressure recovery)
as a truncated Streamline duct - obviously depends on how much truncation you
need to do. But, with only 3-6 inches space, I do believe the Pinched Duct
is a reasonable approach to maintaining high energy boundary layer flow which
penetrates further into the pressure recover region before become slowed enough
to separate.
There! Now I don't have to write that book!
You all know my secret {:>) (well, at least the one about the "Pinched duct")
{:>)
Ed
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