🚀 go-pugleaf

In article <921215012955@avistic.demon.co.uk> lorcan@avistic.demon.co.uk writes:
>In article <1992Dec9.234916.10094@retix.com> bmartin@retix.com writes:
>> Has anyone knoledge of the Cd value of an open box shape, with the
>> open side toward the airflow? Is it better/worse than a flat plate,
>>for example? 
>Worse (ie higher drag). If you've ever seen pictures of a Pelton wheel
>(a type of water turbine) the "paddles" are specially-shaped buckets
>[...]

I think the original question applied to a box without a "bottom".  i.e, a
length of rectangular duct aligned with the stream.  In a reasonably simple
analysis, the only difference in drag between the duct/box and an equivalent
area of flat plate will be due to boundary layer interference in the
interior corners.  If the box is large compared to the boundary layer
thickness, this effect could possibly be neglected.

It should be possible to make a reasonable approximation using standard data
for a rectangular duct for the interior flow, and use flat plate drag on the
outside of the box.  Try Fox & MacDonald or Schlichting for the data.

				Marc Leonard
				leonam@rpi.edu