X-Mozilla-Keys:                                                                                 
Bill Freeman wrote:

Jeff Spitzer wrote:

At 08:36 AM 9/11/99 -0700, you wrote:

Kuchemann & Weber in their McGraw Hill book; The Aerodynamics
of Propulsion surmised that there existed recirculation
in the core due to the low pressure on the back side of
the fins. I find that hard to believe at high dynamic
pressures but I guess it is possible at certain air
speeds.

That's circulation, not recirculation.  Circulation is a aero term used to
model a lifting surface.  The point of the passage is that the fins have
lower speed on the bottom than the top just like a wing due to the angle of
attack.  There is no indication that air flows backwards any more than it
does on your airplane wing.

Jeff Spitzer

Thanks for clarifying that Jeff. I was confused by the little
arrows showing the air flowing backwards through the core.

What do you think the of the increased turbulence idea?

Perhaps what we are seeing is merely the fact that
a thin core in oblique flow has a higher pressure drop
so it is equavalent to a thicker core in axial flow
but it fits in the cowl better than an equavalent thick
core? This is a facinating subject for me and I am
intensely curious on why these oblique flow radiators
seem to be working so well.

BTW do you have the K & W book? I can scan a couple of
more pages on this subject and send them to you.

Paul Lamar

Paul,

With a steep enough angle and a sharp leading edge (like a cooling fin) you
should expect to have separation and early transition to turbulent
separated flow.  This is bad for a wing, but  pretty darned good for
heat transfer.  I think that arrows were just where they were defining
their integration volume to write the equation.  I just skimmed it, tho.

I think it is a simple as "stalling" the cooling fins.  Turbulent flow is MUCH
better at heat transfer than laminar, and the flow will transition from
laminar to turbulen eventually by itself,  but forcing it to happen at the
start
of the fin should be good for heat transfer.

Bill

 
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