Ed, Are you sure the labels are not backwards on the two
duct pressure recovery charts?
Labels are correct, however, I used
two different Y scales for the dynamic pressure on the two charts.
The dynamic pressure values are correct but the unequal scales appear to
give the parabolic curve the greater dynamic pressure recovery, when in
reality it is the streamline duct.
The Y axis on the right is for dynamic
pressure.
I just posted the two charts with their
dynamic pressure scales equal and I think it is clearer now.
Ed Anderson
Ahh! that explains it. The
only thing missing (for me) is that I don't have a mental picture of the
streamline duct shape. In fact, I may have it wrong for the
parabolic as well. I picture the duct area for the parabolic
going up like the chart for the streamline shows it.
I also thought a 7 degree duct was a
simple straight sided duct with sides that diverge at a 7 degree angle
from the centerline. Maybe I'm more confused than I though :
-)
BTW, this is great stuff Ed, keep it
coming!
Tracy
Again, my failure to communicate is
probably at the root of the problem.
The other (blue curves) shown on the
graphs are not the shape (coordinates) of the ducts walls, rather they
represent the area of the duct at that x coordinate point.
So the shapes might appear to present the wrong duct coordinates - but
they are not duct coordinates (:>), they are the duct area at that
coordinate (in square feet).
The reason I did area is that I was using
the continunity of mass equation to derive the air velocity at that x
coordinate using p*V*A (DensityxVelocityxArea) which holds constant
throughout the airflow in the cooling system. So I needed to
calculate the duct area at each X coordinate in order to compute the
velocity at that point which of course I used to calculate the dynamic
pressure at that point.
I probably need to throw in the
curve for the duct wall coordinates as well as that would make it
clearer.
By the way, I have two data point on the
pressure drop across the GM cores. You flight with Paul and one
done by a gent on a test set up. Yours measure around 7.25 inches
h20 and the test stand gave 7.5 inches h20.
I had calculated a pressure drop
coefficient for the GM core based on the dimensions (including space
between fins, etc). If I assume your ducts were closer in
performance to the parabolic ducts then the difference between the
measured and my calculated ranged from 4 - 7%. Since few of us
probably have the low loss of the streamline ducts. I think that is a
fairly good correlation between calcuated pressure drop and
measured.
I am going to assume that is close enough
for me to continue to see if I can develop an "optimum" design with the
GM core and then assuming we don't have room for optimum what effect
which changes might have.
Anyhow, Merry Christmas to you and
Laura. My daughter and son-in-law just came in with our grandsons,
so all for tonight.
Ed Anderson