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Turbulent Breaking of Overturning Gravity Waves Below a Critical Level

Dörnbrack, A. and Gerz, T. and Schumann, U. (1995) Turbulent Breaking of Overturning Gravity Waves Below a Critical Level. Applied Scientific Research, 54, pp. 163-176. DOI: 10.1007/BF00849114

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Official URL: http://www.springerlink.com/content/x115pu7m1g0kv563/

Abstract

The interaction of an internal gravity wave with its evolving critical layer and the subsequent generation of turbulence by overturning waves are studied by three-dimensional numerical simulations. The simulation describes the flow of a stably stratified Boussinesq fluid between a bottom wavy surface and a top flat surface, both without friction and adiabatic. The amplitude of the surface wave amounts to about 0.03 of the layer depth. The horizontal flow velocity is negative near the lower surface, positive near the top surface with uniform shear and zero mean value. The bulk Richardson number is one. The flow over the wavy surface induces a standing gravity wave causing a critical layer at mid altitude. After a successful comparison of a two-dimensional version of the model with experimental observations (Thorpe [21]), results obtained with two different models of viscosity are discussed: a direct numerical simulation (DNS) with constant viscosity and a large-eddy simulation (LES) where the subgrid scales are modelled by a stability-dependent first-order closure. Both simulations are similar in the build-up of a primary overturning roll and show the expected early stage of the interaction between wave and critical level. Afterwards, the flows become nonlinear and evolve differently in both cases: the flow structure in the DNS consists of coherent smaller-scale secondary rolls with increasing vertical depth. On the other hand, in the LES the convectively unstable primary roll collapses into three-dimensional turbulence. The results show that convectively overturning regions are always formed but the details of breaking and the resulting structure of the mixed layer depend on the effective Reynolds number of the flow. With sufficient viscous damping, three-dimensional turbulent convective instabilities are more easily suppressed than two-dimensional laminar overturning.

Item URL in elib:https://elib.dlr.de/32015/
Document Type:Article
Title:Turbulent Breaking of Overturning Gravity Waves Below a Critical Level
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Dörnbrack, A.UNSPECIFIEDUNSPECIFIED
Gerz, T.UNSPECIFIEDUNSPECIFIED
Schumann, U.UNSPECIFIEDUNSPECIFIED
Date:1995
Journal or Publication Title:Applied Scientific Research
Open Access:Yes
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Volume:54
DOI :10.1007/BF00849114
Page Range:pp. 163-176
Status:Published
Keywords:stably stratified shear flow, critical level formation, wave turbulence generation
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EO - Erdbeobachtung
DLR - Research area:Space
DLR - Program:W EO - Erdbeobachtung
DLR - Research theme (Project):W - Vorhaben Atmosphären- und Klimaforschung (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics
Deposited By: DLR-Beauftragter, elib
Deposited On:29 Jan 2008
Last Modified:31 Jul 2019 19:17

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