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Attached is a plot of the Streamline Duct out of K&W vs the optimum 7 Deg
diverging duct. Scale on vertical and horizontal axis is in inches.
According to K&W there is apparently no separation of flow from the duct
wall until the maximum angle is exceeded. Max angle is different depending
on the ratio of your intake area to your core face area. This plot is for a
GM core 9" high.
The coordinates provided by K&W have been normalized on both axis, so you
have to use those normalized values to scale you actual/real values. But,
you can do it for any size core.
The basic point here is that apparently you can use a streamline duct and
still preclude boundary layer separation (until the last inch or so before
the core where it interferes much less as it separates (if it does at all)
far around the curve as shown by the red arrow.
Perhaps you've notice that the streamline duct coordinates get to a
reasonable inlet size much, much quicker than the optimum 7 Deg duct. Even
at 15" on the chart the 7deg duct would have an inlet size of approx 5"
high. So if you wanted a inlet duct of 24 square inches (say 4 high x 6
wide), you would need to extend the duct to somewhere around 16-17". The
streamline duct has on the other hand could support a 4" high duct around
3-4 inches out from the face. If you did make it that short, then I think
you
would probably incur more loses than optimum, but still perhaps the best
compromise if you don't have room for the optimum duct length required.
This is basically the curve I used when I reduced one of my two radiator
inlet ducts down from 24 square inches to around 9 square inches with only a
5F increase in cooling temps.
I'll have a spreadsheet in a day or so if anyone is interested in playing
with it.
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
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