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On the sheared density interface of an entraining stratified fluid

Published online by Cambridge University Press:  21 April 2006

Siavash Narimousa  and
Harindra J. S. Fernando
Siavash Narimousa
Affiliation:
Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, MD 21218, USA Present address: Department of Mechanical Engineering, University of Southern California, Los Angeles, CA 90089, USA.
Harindra J. S. Fernando
Affiliation:
Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, MD 21218, USA Present address: Department of Environmental Engineering Science, California Institute of Technology, Pasadena, CA 91125, and Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, AZ 85287, USA.
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Abstract

This paper deals with the nature of the entrainment interface of a two-layer fluid subjected to interfacial velocity shear. The shear flow was generated by driving the mixed layer over the dense layer by a disk pump such that there is no stress at the top of the mixed layer. During the entrainment process a sharp, thin-density interfacial layer developed; its thickness δ was found to increase linearly with the mixed-layer depth h, independent of the Richardson number Riu. The shear layer thickness δs was found to be much larger than δ and the ratio δs/h is also found to be constant, irrespective of Riu. At the entrainment interface, the estimated buoyancy flux and the dissipation of turbulent kinetic-energy appear to be of the same order. This result supports an entrainment law of the form E ∼ Riu−1, where E is the entrainment coefficient. The interfacial layer showed sporadic large-amplitude wave oscillations whose amplitudes scaled well with the estimated size of the undulations caused by the impingement of large eddies (of size h) on the density interface. The density-interfacial layer was found to be ‘topped’ by a layer of partially mixed fluid which had not yet incroporated into the well-mixed region.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 174 , January 1987 , pp. 1 - 22
Copyright
© 1987 Cambridge University Press

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