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Secondary Kelvin–Helmholtz instability in weakly stratified shear flow


The growth of secondary vortices on the braids separating Kelvin–Helmholtz billows is investigated via numerical simulations. The similarity theory of Corcos & Sherman (1976) is extended to include mixing processes with Prandtl number greater than unity, and is shown to provide a useful description of the physics of the braid regions just prior to the onset of secondary instability. The numerical study of Staquet (1995) is extended to include a wider range of Prandtl numbers and bulk Richardson numbers. Length and time scales of the secondary instability are compared with predictions based on normal-mode stability analysis of the braids. The onset of instability is shown to be accompanied by a dramatic increase in mixing efficiency in the braid region, emphasizing the potential importance of preturbulent Kelvin–Helmholtz billows for mixing stratified fluids.

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Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
  • URL: /core/journals/journal-of-fluid-mechanics
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