REFLECTOR:NACA inlet shape
Al Gietzen
reflector@tvbf.org
Sat, 16 Aug 2003 10:55:41 -0700
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Chris;
Here's my take FWIW. There are two factors that are different about
cooling liquid-to-air heat exchangers vs cooling the fins of an
air-cooled engine, and these factors influence whether a NACA scoop will
work or not. The first is that the core matrix (tube and fin density)
of a typical radiator or oil cooler; while more efficient for heat
transfer, requires more pressure drop for a given flow than the much
lower fin density of the air cooled engine. The second is that the
average fin temperature of the air-cooled engine is much higher than is
allowed by water/glycol, or oil, so the air-side temp increase for the
liquid heat exchangers is less; therefore the amount of air flow
required is greater.
There is some tradeoff in these two factors - more pressure drop =
greater efficiency = lower air flow, so the higher density core of the
heat exchanger helps offset the higher flow requirement caused by the
lower delta T of the air. But in general, the optimum radiator is going
to require higher pressure and higher total air flow.
The submerged scoop gives lower dynamic pressure recovery than a well
designed ram scoop, and for the same inlet area, lower flow because of
boundary layer ingestion. These are the reasons that the original
designers say that it is generally not "recommended" for heat
exchangers. So the fact that it works for a given HP air-cooled engine
does not mean that it will work for the same power liquid cooled engine.
Does it mean it can't work? No. There are a lot of factors involved.
There are certified airplanes using submerged inlets for oil coolers.
They apparently work fine. Do you want to try it; and risk having to
change things later? That's a choice you get to make.
My opinion is this. Any air you take on board, slow down, manipulate,
etc; causes drag; no matter what type of scoop. A well designed ram
scoop, proper handling of the air, and proper exit fairing has little if
any more drag than a submerged scoop to do the same job. The opening of
a protruding ram scoop doesn't count as frontal area because the air is
going in. With a good boundary layer divider and a scoop shaped to
retain attached flow the effects are minimal. If you're taking on air
where you don't need high pressure recovery use NACA type scoop; if you
need high pressure recovery use a ram scoop.
The original Velocity arm pit scoops do not qualify as well designed ram
scoops.
Al
-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org] On
Behalf Of Christopher Barber
Sent: Thursday, August 14, 2003 11:53 AM
To: reflector@tvbf.org
Subject: RE: REFLECTOR:NACA inlet shape
I have seen it expressed though that according to that original research
that NACA scoops are not really suited for application of heat exchange
cooling. I need it to cool a radiator in my application. Those that
know more than I seem adamant that they do not work well (even making
reference to an alleged Velocity builder/flyer who hates them). However,
it seems as if Velocity, Inc. overall has had good results. Any of you
engineering (or programmers, or burger flippers etc) types have any
thoughts on this.
Thanks for your insight and experience.
All the best,
Chris
Christopher Barber
Attorney and Counselor at Law
11930 S Sam Houston Pkwy E
Suite 103
Houston, Texas 77089-4755
281-464-LAWS (5297)
281-754-4168 (Fax)
"Serving the needs of Senior Texans"
CBarber@TexasAttorney.net
www.TexasAttorney.net
-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf Of Tony Babb
Sent: Tuesday, August 12, 2003 7:41 PM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:NACA inlet shape
For the real enthusiast you can download the original NACA research
paper written in 1945. I'm not at home and don't have the reference but
if you go to www.larc.nasa.gov and then search their archive you should
be able to find it OK. The file is called naca-acr-5120.pdf it's about
12MB, title is "An experimental investigation of NACA submerged-duct
entrances".
In there you'll find recommendations for the shape of the duct and also
the shape of the lip on the wide end of the duct.
Fascinating stuff..
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<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>Chris;</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>Here’s my take FWIW. =
There
are two factors that are different about cooling liquid-to-air heat =
exchangers vs
cooling the fins of an air-cooled engine, and these factors influence =
whether a
NACA scoop will work or not. The first is that the core matrix =
(tube and
fin density) of a typical radiator or oil cooler; while more efficient =
for heat
transfer, requires more pressure drop for a given flow than the much =
lower fin
density of the air cooled engine. The second is that the average =
fin
temperature of the air-cooled engine is much higher than is allowed by
water/glycol, or oil, so the air-side temp increase for the liquid heat
exchangers is less; therefore the amount of air flow required is =
greater.</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>There is some tradeoff in these =
two
factors – more pressure drop =3D greater efficiency =3D lower air =
flow, so
the higher density core of the heat exchanger helps offset the higher =
flow
requirement caused by the lower delta T of the air. But in =
general, the optimum
radiator is going to require higher pressure and higher total air =
flow.</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>The submerged scoop gives lower =
dynamic
pressure recovery than a well designed ram scoop, and for the same inlet =
area,
lower flow because of boundary layer ingestion. These are the =
reasons that
the original designers say that it is generally not =
“recommended”
for heat exchangers. So the fact that it works for a given HP air-cooled =
engine
does not mean that it will work for the same power liquid cooled =
engine.</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>Does it mean it can’t =
work?
No. There are a lot of factors involved. There are certified
airplanes using submerged inlets for oil coolers. They apparently work =
fine. Do
you want to try it; and risk having to change things later? =
That’s a
choice you get to make. </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>My opinion is this. Any air =
you
take on board, slow down, manipulate, etc; causes drag; no matter what =
type of
scoop. A well designed ram scoop, proper handling of the air, and =
proper
exit fairing has little if any more drag than a submerged scoop to do =
the same
job. The opening of a protruding ram scoop doesn’t count as =
frontal
area because the air is going in. With a good boundary layer divider and =
a
scoop shaped to retain attached flow the effects are minimal. If =
you’re
taking on air where you don’t need high pressure recovery use NACA =
type
scoop; if you need high pressure recovery use a ram =
scoop.</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>The original Velocity arm pit =
scoops do
not qualify as well designed ram scoops.</span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'>Al </span></font></p>
<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DVerdana><span =
style=3D'font-size:
11.0pt;font-family:Verdana;color:blue'> </span></font></p>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
face=3DTahoma><span
style=3D'font-size:10.0pt;font-family:Tahoma'>-----Original =
Message-----<br>
<b><span style=3D'font-weight:bold'>From:</span></b> =
reflector-admin@tvbf.org
[mailto:reflector-admin@tvbf.org] <b><span style=3D'font-weight:bold'>On =
Behalf
Of </span></b>Christopher Barber<br>
<b><span style=3D'font-weight:bold'>Sent:</span></b> Thursday, August =
14, 2003
11:53 AM<br>
<b><span style=3D'font-weight:bold'>To:</span></b> =
reflector@tvbf.org<br>
<b><span style=3D'font-weight:bold'>Subject:</span></b> RE: =
REFLECTOR:NACA inlet
shape</span></font></p>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
color=3Dblue
face=3DGaramond><span =
style=3D'font-size:12.0pt;font-family:Garamond;color:blue'>I
have seen it expressed though that according to that original research =
that
NACA scoops are not really suited for application of heat exchange
cooling. I need it to cool a radiator in my application. Those =
that know
more than I seem adamant that they do not work well (even making =
reference to
an alleged Velocity builder/flyer who hates them). However, it seems as =
if
Velocity, Inc. overall has had good results. Any of you
engineering (or programmers, or burger flippers etc) types have any
thoughts on this. </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
color=3Dblue
face=3DGaramond><span =
style=3D'font-size:12.0pt;font-family:Garamond;color:blue'>Thanks
for your insight and experience.</span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
color=3Dblue
face=3DGaramond><span =
style=3D'font-size:12.0pt;font-family:Garamond;color:blue'>All
the best,</span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
color=3Dblue
face=3DGaramond><span =
style=3D'font-size:12.0pt;font-family:Garamond;color:blue'>Chris</span></=
font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<p style=3D'margin-left:.5in'><font size=3D2 face=3D"Times New =
Roman"><span
style=3D'font-size:10.0pt'>Christopher Barber<br>
Attorney and Counselor at Law<br>
11930 S Sam Houston Pkwy E<br>
Suite 103<br>
Houston, Texas 77089-4755<br>
281-464-LAWS (5297)<br>
281-754-4168 (Fax)<br>
<br>
"Serving the needs of Senior Texans"<br>
<br>
CBarber@TexasAttorney.net<br>
www.TexasAttorney.net </span></font></p>
<blockquote =
style=3D'margin-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'>
<p class=3DMsoNormal =
style=3D'margin-right:0in;margin-bottom:12.0pt;margin-left:
.5in'><font size=3D2 face=3DTahoma><span =
style=3D'font-size:10.0pt;font-family:Tahoma'>-----Original
Message-----<br>
<b><span style=3D'font-weight:bold'>From:</span></b> =
reflector-admin@tvbf.org
[mailto:reflector-admin@tvbf.org]<b><span style=3D'font-weight:bold'>On =
Behalf Of
</span></b>Tony Babb<br>
<b><span style=3D'font-weight:bold'>Sent:</span></b> Tuesday, August 12, =
2003
7:41 PM<br>
<b><span style=3D'font-weight:bold'>To:</span></b> =
reflector@tvbf.org<br>
<b><span style=3D'font-weight:bold'>Subject:</span></b> Re: =
REFLECTOR:NACA inlet
shape</span></font></p>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>For the real enthusiast you =
can
download the original NACA research paper written in 1945. I'm not at =
home and
don't have the reference but if you go to <a
href=3D"http://www.larc.nasa.gov">www.larc.nasa.gov</a> and then search =
their archive
you should be able to find it OK. The file is called =
naca-acr-5120.pdf
it's about 12MB, title is "An experimental investigation of NACA
submerged-duct entrances".</span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>In there you'll find =
recommendations
for the shape of the duct and also the shape of the lip on the wide end =
of the
duct. </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D3 =
face=3D"Times New Roman"><span
style=3D'font-size:12.0pt'> </span></font></p>
</div>
<div>
<p class=3DMsoNormal style=3D'margin-left:.5in'><font size=3D2 =
face=3DArial><span
style=3D'font-size:10.0pt;font-family:Arial'>Fascinating =
stuff..</span></font></p>
</div>
</blockquote>
</div>
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