Enhanced spin-up

Many years ago I had the opportunity of doing a small amount of experimental work in fluid dynamics, in the laboratory which Raymond Hide then ran at the Meteorological Office. I was working, with a colleague, on the effect of `bumps' on fluid spin-up in a rotating circular cylinder. We found that small changes in the boundary geometry had little effect if they were symmetric about the rotation axis, but that non-axisymmetric changes could affect the spin-up time quite substantially, especially at relatively high Rossby numbers (~0.25).

In particular, a bar of square cross-section, attached to the base along a diameter, and with a height only 5 per cent of the cylinder height, decreased the spin-up time by a factor of 7. So far as I am aware, this substantial effect of non-axisymmetric `bumps' has never been reported in the scientific literature, and would seem to merit further investigation.

(Note: Extensive recent work on this problem by Richard Hewitt
at Manchester University can now be found here.)

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