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Title: Controls on Turbulent Mixing in a Strongly Stratified and Sheared Tidal River Plume

Abstract

Considerable effort has been made to parameterize turbulent kinetic energy (TKE) dissipation rate ..epsilon.. and mixing in buoyant plumes and stratified shear flows. Here, a parameterization based on Kunze et al. is examined, which estimates ..epsilon.. as the amount of energy contained in an unstable shear layer (Ri < Ric) that must be dissipated to increase the Richardson number Ri = N2/S2 to a critical value Ric within a turbulent decay time scale. Observations from the tidal Columbia River plume are used to quantitatively assess the relevant parameters controlling ..epsilon.. over a range of tidal and river discharge forcings. Observed ..epsilon.. is found to be characterized by Kunze et al.'s form within a factor of 2, while exhibiting slightly decreased skill near Ri = Ric. Observed dissipation rates are compared to estimates from a constant interfacial drag formulation that neglects the direct effects of stratification. This is found to be appropriate in energetic regimes when the bulk-averaged Richardson number Rib is less than Ric/4. However, when Rib > Ric/4, the effects of stratification must be included. Similarly, ..epsilon.. scaled by the bulk velocity and density differences over the plume displays a clear dependence on Rib, decreasing as Rib approaches Ric.more » The Kunze et al. ..epsilon.. parameterization is modified to form an expression for the nondimensional dissipation rate that is solely a function of Rib, displaying good agreement with the observations. It is suggested that this formulation is broadly applicable for unstable to marginally unstable stratified shear flows.« less

Authors:
; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1324537
Report Number(s):
NREL/JA-5000-67093
Journal ID: ISSN 0022-3670
DOE Contract Number:
AC36-08GO28308
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Oceanography; Journal Volume: 46; Journal Issue: 8
Country of Publication:
United States
Language:
English
Subject:
16 TIDAL AND WAVE POWER; geographic location/entity; estuaries; circulation/dynamics; coastal flows; mixing; shear structure/flows; turbulence

Citation Formats

Jurisa, Joseph T., Nash, Jonathan D., Moum, James N., and Kilcher, Levi F.. Controls on Turbulent Mixing in a Strongly Stratified and Sheared Tidal River Plume. United States: N. p., 2016. Web. doi:10.1175/JPO-D-15-0156.1.
Jurisa, Joseph T., Nash, Jonathan D., Moum, James N., & Kilcher, Levi F.. Controls on Turbulent Mixing in a Strongly Stratified and Sheared Tidal River Plume. United States. doi:10.1175/JPO-D-15-0156.1.
Jurisa, Joseph T., Nash, Jonathan D., Moum, James N., and Kilcher, Levi F.. 2016. "Controls on Turbulent Mixing in a Strongly Stratified and Sheared Tidal River Plume". United States. doi:10.1175/JPO-D-15-0156.1.
@article{osti_1324537,
title = {Controls on Turbulent Mixing in a Strongly Stratified and Sheared Tidal River Plume},
author = {Jurisa, Joseph T. and Nash, Jonathan D. and Moum, James N. and Kilcher, Levi F.},
abstractNote = {Considerable effort has been made to parameterize turbulent kinetic energy (TKE) dissipation rate ..epsilon.. and mixing in buoyant plumes and stratified shear flows. Here, a parameterization based on Kunze et al. is examined, which estimates ..epsilon.. as the amount of energy contained in an unstable shear layer (Ri < Ric) that must be dissipated to increase the Richardson number Ri = N2/S2 to a critical value Ric within a turbulent decay time scale. Observations from the tidal Columbia River plume are used to quantitatively assess the relevant parameters controlling ..epsilon.. over a range of tidal and river discharge forcings. Observed ..epsilon.. is found to be characterized by Kunze et al.'s form within a factor of 2, while exhibiting slightly decreased skill near Ri = Ric. Observed dissipation rates are compared to estimates from a constant interfacial drag formulation that neglects the direct effects of stratification. This is found to be appropriate in energetic regimes when the bulk-averaged Richardson number Rib is less than Ric/4. However, when Rib > Ric/4, the effects of stratification must be included. Similarly, ..epsilon.. scaled by the bulk velocity and density differences over the plume displays a clear dependence on Rib, decreasing as Rib approaches Ric. The Kunze et al. ..epsilon.. parameterization is modified to form an expression for the nondimensional dissipation rate that is solely a function of Rib, displaying good agreement with the observations. It is suggested that this formulation is broadly applicable for unstable to marginally unstable stratified shear flows.},
doi = {10.1175/JPO-D-15-0156.1},
journal = {Journal of Physical Oceanography},
number = 8,
volume = 46,
place = {United States},
year = 2016,
month = 8
}
  • Abstract not provided.
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