if the free air velocity (160)
converts to 12"H20 and you had a streamline duct inlet actual had that
coming in then theoretically you could get approx 12 * .84 = 10.8" inside
the duct. Since you measured 3.25" static in front of the core, that
would indicate a significant lack of pressure recovery inside your duct (what
ever the reason). There are several reasons this
might be happening.
I think the confusion here is whether we’re
talking “dynamic” pressure or “static” pressure. Are
you saying that the maximum static pressure in the duct is 0.84 of the dynamic
pressure at the entrance to the duct? If that is true, I have been under a misconception.
I measured 9.5” dynamic pressure out in front of the scoop; and 3.25”
static pressure near the face of the core – just below the midpoint.
1. The air flow and velocity
is considerably reduced from what you are expecting (too small opening/exit -
which I don't believe to be the case)
2. The boundary layer is a
significant part of your duct total air flow and as a consequence
its lesser velocity has less dynamic pressure potential.
3. A significant part of your
duct flow is chaotic with eddies which does not provide recoverable pressure -
or it is much reduced. (The boundary layer could be contributing to this)
4. Some combination of the
above.
Right, now I would suspect that
the boundary layer could be the culprit in that it can contribute to 2 and 3
above. But, as you know, this is speculation on my part
I’m sure you’re
right; a combination of 2 and 3. Yesterday I measured the static pressure near
the upper surface of the duct; an inch or so in front of the core – less
than 0.25” H2O. That confirmed to me that the “flow is chaotic with eddies”, as you say. I
think the addition of a vane is worth a try.
Al