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Singularity formation during Rayleigh–Taylor instability

Published online by Cambridge University Press:  26 April 2006

Gregory Baker ,
Russel E. Caflisch  and
Michael Siegel
Gregory Baker
Affiliation:
Mathematics Department, The Ohio State University, Columbus, OH 43210, USA
Russel E. Caflisch
Affiliation:
Mathematics Department, UCLA, Los Angeles, CA 90024, USA
Michael Siegel
Affiliation:
Mathematics Department, The Ohio State University, Columbus, OH 43210, USA
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Abstract

During the motion of a fluid interface undergoing Rayleigh-Taylor instability, vorticity is generated on the interface baronclinically. This vorticity is then subject to Kelvin-Helmholtz instability. For the related problem of evolution of a nearly flat vortex sheet without density stratification (and with viscosity and surface tension neglected), Kelvin-Helmholtz instability has been shown to lead to development of curvature singularities in the sheet. In this paper, a simple approximate theory is developed for Rayleigh-Taylor instability as a generalization of Moore's approximation for vortex sheets. For the approximate theory, a family of exact solutions is found for which singularities develop on the fluid interface. The resulting predictions for the time and type of the singularity are directly verified by numerical computation of the full equations. These computations are performed using a point vortex method, and singularities for the numerical solution are detected using a form fit for the Fourier components at high wavenumber. Excellent agreement between the theoretical predictions and the numerical results is demonstrated for small to medium values of the Atwood number A, i.e. for A between 0 and approximately 0.9. For A near 1, however, the singularities actually slow down when close to the real axis. In particular, for A = 1, the numerical evidence suggests that the singularities do not reach the real axis in finite time.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 252 , July 1993 , pp. 51 - 78
Copyright
© 1993 Cambridge University Press

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