Wavelength scaling of spiral patterns formed by granular media underneath a rotating fluid

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Abstract
A spiral pattern formed by granular media underneath a rotating fluid is discussed. Results from a cellular-automaton model are compared to experimental data, and are found to reproduce experimentally observed scalings. A theoretical argument predicting these scalings on the basis of the existence of a critical threshold condition is advanced. It is suggested that the pattern is probably not associated with a hitherto unknown flow instability, as has been speculated previously. It appears that the pattern constitutes some rotating analog to sand ripples in nonrotating systems.