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Hey, Dave
You have sat through just too many
presentations - your skepticism shows through (I sat through 26 years of
briefings in the Air Force and another 15 as a contractor - give me enough graph
paper and the right scale and I can prove anything you
want{:>).
Actually, I could have thrown a few more slides in adding
more information supporting my deductive reasoning - but no one/no where
has published any data on a "pinched" duct {:>) - and more words would be
just that - more words. It was not intended to be a research paper - just
a informal presentation to folks with a common interest.
But, to answer your question - No data at all. and
therefore I get to "write the rules". I
can only take the credit (or blame) for the pinched duct concept all of the rest
of the information is available in documents or on the web. However,
I DID NOT invent the words about boundary layer separation and ducts and
their effect on cooling.
It appear to follow ( from what I think I understand
about boundary layers in a duct) and my installation constraints.
Higher energy boundary layers penetrate further into the pressure recovery
zone (expansion area) than lower energy boundary layers. Ergo - if I
increase the energy of that boundary layer, it will penetrate further and
separate later. If that is not correct then my basic assumption is flawed.
Again,certainly not claming superior or performance even close to par with
the streamline duct.
I was faced with truncating a streamline duct
which with only 3-6" to play with would have left the inlet opening around 75%
the area of my core - not appealing from a drag standpoint. With the
pinched duct, I can keep the size of the opening even smaller than the
streamline duct calls for, with the pinched area I can speed up the air velocity
thereby adding more energy to the boundary layer, which hopefully causes
it to penetrate further into the pressure recovery zone before separating
and all ends well - it cools.
Again, I am not trying to sell anything to anybody - those
are the conclusions I came to and applied - others are welcome to do their own
research and come up with something better. I spent weeks going over
chapter 12 of K&W and working through each equation (well, there was perhaps
1 or 2 I had to take Mr. Kuchman's word for {:>).). That does not mean
my understanding is not flawed - but, its the best I can do.
I admit this is an exercise in what I hope is
deductive logic - not data verified experiment. I hope you do
not expect me to rationally defend it with data - when I don't have any
data and no interest in taking the time and effort to instrument {:>).
So everyone is certainly free to draw their own
conclusions. I may be wrong, but until somebody points out exactly where
my deductive reasoning is flawed, I'm going to keep on flying with those pinched
ducts.{:>)
Ed
----- Original Message -----
Sent: Wednesday, February 28, 2007 9:19
PM
Subject: [FlyRotary] Re: Diffuser Design
Rules
Hi Ed,
Pretty slides. They SEEM authoritative but who gets to write
the "rules"? :-) In other words, where is the rest of the
data. I completely agree that a streamline duct is better than the
conventional duct, and that separation needs to be avoided. But do
you have any data comparing a restricted neck style to a regular streamline
duct?
Dave Leonard
Once again, the only "creative" bit of thinking on
my part was the pinched duct in order to cope with the limitations of
having a very small area for a duct. All the rest of the credit
belongs to K&W and Horner as well as few others.
Ed
--
David
Leonard
Turbo Rotary RV-6 N4VY
My websites at:
http://members.aol.com/_ht_a/rotaryroster/index.html
http://members.aol.com/_ht_a/vp4skydoc/index.html
http://leonardiniraq.blogspot.com
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