Hostname: page-component-848d4c4894-wg55d Total loading time: 0 Render date: 2024-05-20T18:57:49.775Z Has data issue: false hasContentIssue false

Moffatt eddies in the cone

Published online by Cambridge University Press:  05 September 2005

P. N. SHANKAR
Affiliation:
Computational and Theoretical Fluid Dynamics Division, National Aerospace Laboratories, Bangalore 560 017, Indiapn_shankar55@rediffmail.com Present address: 33/1 Kasturba Road Cross, Bangalore 560 001, India.

Abstract

Consider Stokes flow in a cone of half-angle $\alpha$ filled with a viscous liquid. It is shown that in spherical polar coordinates there exist similarity solutions for the velocity field of the type $r^{\lambda} {\bm f}(\theta;\lambda)\exp{\rm i}m\phi $ where the eigenvalue $\lambda$ satisfies a transcendental equation. It follows, by extending an argument given by Moffatt (1964$a$), that if the eigenvalue $\lambda$ is complex there will exist, associated with the corresponding vector eigenfunction, an infinite sequence of eddies as $r\,{\rightarrow}\, 0$. Consequently, provided the principal eigenvalue is complex and the driving field is appropriate, such eddy sequences will exist. It is also shown that for each wavenumber $m$ there exists a critical angle $\alpha^*$ below which the principal eigenvalue is complex and above which it is real. For example, for $m\,{=}\,1$ the critical angle is about $74.45^{\circ}$. The full set of real and complex eigenfunctions, the inner eigenfunctions, can be used to compute the flow in a cone given data on the lid. There also exist outer eigenfunctions, those that decay for $r\,{\rightarrow}\, \infty$, and these can be generated from the inner ones. The two sets together can be used to calculate the flow in a conical container whose base and lid are spherical surfaces. Examples are given of flows in cones and in conical containers which illustrate how $\alpha$ and $r_0$, a length scale, affect the flow fields. The fields in conical containers exhibit toroidal corner vortices whose structure is different from those at a conical vertex; their growth and evolution to primary vortices is briefly examined.

Type
Papers
Copyright
© 2005 Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)