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Experiments on Ekman layer instability

Published online by Cambridge University Press:  28 March 2006

P. R. Tatro and
E. L. Mollo-Christensen
P. R. Tatro
Affiliation:
Massachusetts Institute of Technology Department of Meteorology
E. L. Mollo-Christensen
Affiliation:
Massachusetts Institute of Technology Department of Meteorology
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Abstract

Laboratory measurements were made of the instabilities of the Ekman layer using hot wire anemometers. The apparatus consisted of two parallel circular rotating plates forming a spool; the air was admitted through screens at the outer edge and removed through a screen cage at the hub. In the Ekman layers formed on the inner surfaces of the plates, measurements were made of the mean velocities as functions of r and a; the velocity fluctuations were also measured.

It appears that the instability labelled type II by Faller always occurs first, and at zero Rossby number the critical Reynolds number is 56 ± 2. This instability originates in the boundary layer, but at slightly higher Reynolds number the fluctuations persist far into the geostrophic region, probably as inertial waves excited by the boundary-layer fluctuations.

At higher Reynolds number another instability appears of shorter wavelength and slower speed. This instability is confined to the boundary layer and is apparently the type I reported by Faller.

The phase speeds, frequencies, and wave-front orientations of both type instabilities have been measured.

Information

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 28 , Issue 3 , 26 May 1967, pp. 531 - 543
Copyright
© 1967 Cambridge University Press

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