Monday, April 06, 2009

What a drag

I've spent a busy but interestingly different day spent investigating drag coefficients for my newest project on the cool material entrained within starburst-driven superwinds. Although wikipedia has some useful background information its hard to track down exact references, and to determine the exact Reynold numbers over which the drag coefficients apply.

And pretty much all of the numbers I can find apply to rigid bodies in incompressible flows, whereas I'm interested in deformable clouds embedded in supersonic flows, and in particular sources of information other than the few astrophysical papers that mention cloud drag coefficients (for reasons that are too complicated to explain here).

There quite a few non-astro papers on liquid droplets, e.g. water droplets, both experimental and numerical, but almost all are in the low Reynolds number limit (i.e. Stokes drag).

Ultimately I failed to find exactly what I was looking for, but in the process I did come across this paper:

The drag force on an American football

Am. J. Phys. 71, 791 (2003)

Its neat the someone actually went out and built an experimental apparatus to measure the drag coefficient of a football. In case you're interested, CD is ~0.05 - 0.06 for Re > 1e5.

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