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On the dynamics of turbulence near a free surface

Published online by Cambridge University Press:  22 May 2017

Oscar Flores*
Affiliation:
Departamento de Bioingeniería e Ingeniería Aeroespacial, Universidad Carlos III de Madrid, 28911 Leganés, Spain
James J. Riley
Affiliation:
Department of Mechanical Engineering, University of Washington, Seattle, WA 98195, USA
Alexander R. Horner-Devine
Affiliation:
Department of Civil and Environmental Engineering, University of Washington, Seattle, WA 98195, USA
*
Email address for correspondence: oflores@ing.uc3m.es

Abstract

We report on direct numerical simulations to examine the spectral behaviour of turbulence close to and at a flat, stress-free surface. We find, consistent with field measurements near such a free surface, that an inertial-range type of behaviour is obtained for the horizontal components of the velocity at and near the stress-free surface, at horizontal wavelengths for which the vertical velocity is much smaller than the horizontal components. At approximately an integral length scale from the stress-free surface, the flow has adjusted back to more classical isotropic turbulence. The behaviour of the turbulence near the stress-free surface is similar to that observed recently for strongly stratified flows, and we argue that the causes of that behaviour are the same in both flows: the suppression of the large-scale vertical velocity and the allowance of strong vertical shearing of the horizontal velocity leading to a downscale transfer of energy and to the development of the $-5/3$ spectra for the horizontal velocities.

Type
Papers
Copyright
© 2017 Cambridge University Press 

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