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Type: Journal article
Title: Unsteady flow in a rotating torus after a sudden change in rotation rate
Author: Hewitt, Richard E.
Hazel, Andrew
Clarke, Richard John
Denier, James Patrick
Citation: Journal of Fluid Mechanics, 2011; 688:88-119
Publisher: Cambridge University Press
Issue Date: 2011
ISSN: 0022-1120
School/Discipline: School of Mathematical Sciences
Statement of
R. E. Hewitt, A. L. Hazel, R. J. Clarke and J. P. Denier
Abstract: We consider the temporal evolution of a viscous incompressible fluid in a torus of finite curvature; a problem first investigated by Madden & Mullin (J. Fluid Mech., vol. 265, 1994, pp. 265–217). The system is initially in a state of rigid-body rotation (about the axis of rotational symmetry) and the container’s rotation rate is then changed impulsively. We describe the transient flow that is induced at small values of the Ekman number, over a time scale that is comparable to one complete rotation of the container. We show that (rotationally symmetric) eruptive singularities (of the boundary layer) occur at the inner or outer bend of the pipe for a decrease or an increase in rotation rate respectively. Moreover, on allowing for a change in direction of rotation, there is a (negative) ratio of initial-to-final rotation frequencies for which eruptive singularities can occur at both the inner and outer bend simultaneously. We also demonstrate that the flow is susceptible to a combination of axisymmetric centrifugal and non-axisymmetric inflectional instabilities. The inflectional instability arises as a consequence of the developing eruption and is shown to be in qualitative agreement with the experimental observations of Madden & Mullin (1994). Throughout our work, detailed quantitative comparisons are made between asymptotic predictions and finite- (but small-) Ekman-number Navier–Stokes computations using a finite-element method. We find that the boundary-layer results correctly capture the (finite-Ekman-number) rotationally symmetric flow and its global stability to linearised perturbations.
Keywords: boundary-layer stability, pipe flow boundary layer
Rights: Copyright Cambridge University Press 2011
DOI: 10.1017/jfm.2011.366
Appears in Collections:Environment Institute publications
Mathematical Sciences publications

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