|
|
The only purpose of the example was to show that when
you switch from a thin to thick radiator, or large
frontal area to a small frontal area, or both at the
same time, that the mass flow can change significantly
even though the inlet opening did not change. There
was some debate over that.
--- Tracy Crook <tracy@rotaryaviation.com> wrote:
The example is just fine but it has little to do
with an aircraft
engine cooling system. I was waiting to pounce on
you for suggesting
that the lowest drag would result from a rad with
the lowest
restriction but you didn't go there.
Consider this example: The drag brakes installed on
some aircraft are
essentially small flat plates extended into the
airstream. Those
plates have large HOLES in them. They make more
drag that way. Is
that intuitive?
What I'm getting at is that ANY practical radiator
is going to chew up
virtually all of the energy in the airstream that
passes through it.
It is only a pipe dream that a free(er) flowing
radiator is going to
give less drag than one with a higher pressure drop.
For other
reasons, the opposite is usually true.
Tracy (brain dead at 02:21 )
On Nov 13, 2007 9:17 PM, Ron Springer
<ron2369@sbcglobal.net> wrote:
> How's this example?
>
> Let's say you have an inlet opening of a given
area
> and downstream of that is a constant area duct at
the
> same area. At the exit of the duct is a door flap
that
> can be set to anything from fully open to fully
> closed.
>
> When the door is fully open you will get the max
flow
> through the duct. It might be 99%+ of the
freestream
> flow at that same cross-sectional area.
>
> When the door is fully closed you get zero flow
> through the duct. All flow streamlines steer right
> around the inlet opening. This is a pitot tube
> basically.
>
> When the door is set to an intermediate position,
you
> can get any flow you want through the duct
(between
> zero and max) and the inlet area is the same.
>
> Changing door positions is like swapping in and
out
> different radiators and ductwork that have
different
> flow resistances. When going to a higher
resistance
> radiator (for instance, one with smaller frontal
area,
> a thicker core, and the same fin spacing) it is
like
> closing the door a bit. The air flow will
decrease.
>
> So, my point is that you can get any flow from
zero to
> max flow through an inlet by changing the
downstream
> flow losses.
>
> Ron
>
> --
> Homepage: http://www.flyrotary.com/
> Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
>
--
Homepage: http://www.flyrotary.com/
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
|
|