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Instabilities in channel flow with system rotation

A flow visualization study of instabilities caused by Coriolis effects in plane rotating Poiseuille flow has been carried out. The primary instability takes the form of regularly spaced roll cells aligned in the flow direction. They may occur at Reynolds numbers as low as 100, i.e. almost two orders of magnitude lower than the critical Reynolds number for Tollmien-Schlichting waves in channel flow without rotation. The development of such roll cells was studied as a function of both the Reynolds number and the rotation rate and their properties compared with results from linear spatial stability theory. The theoretically obtained most unstable wavenumber agrees fairly well with the experimentally observed value. At high Reynolds number a secondary instability sets in, which is seen as a twisting of the roll cells. A wavytype disturbance is also seen at this stage which, if the rotational speed is increased, develops into large-scale ‘turbulence’ containing imbedded roll cells.