Abstract/Details

Turbulent mixing in stably stratified flows


2007 2007

Other formats: Order a copy

Abstract (summary)

High resolution direct numerical simulations are used to investigate the dynamics of turbulence in flows subject to strong stable stratification, which are common in natural settings. Results are presented for two categories of simulations, uniform and non-uniform density stratification. For all simulated flows, the density stratification was held constant in time, and there was no ambient shear. Flows with uniform density stratification are first analyzed to help provide clear insight to physical processes, followed by flows with non-uniform density stratification which better represent the stratification occurring in nature. Areas of non-uniform density stratification include thermohaline staircases and atmospheric layer transitions.

For uniform density gradient flows, it is observed that the Froude-Reynolds number scaling developed by Riley and de Bruyn Kops [2003] is similar to the buoyancy Reynolds number, Reb = &egr;/νN2. This supports the use of two dimensionless parameters obtained from dimensional analysis to predict turbulence in a density stratified flow. Also, due to the intermittent nature of density stratified flows, an auto-correlation length scale may be more appropriate than the typical advective length scale Ł a = [special characters omitted]. Finally, the common assumption that kinetic energy dissipation rate &egr; can be approximated by the vertical shear is shown to be valid only when Re b ≤ [special characters omitted](1).

Non-uniformly stratified flows are often characterized simply by the average density change with height, which may not adequately describe the flow. For simulated wake flows with the same average density stratification, but altered vertical stratification profiles, the flow dynamics are seen to depend on the ratio ξ = δu ρ, where δu and δρ are characteristic wake and stratification vertical length scales. When ξ is monotonically increased from 0.01 (near linear stratification) to 2 (wake height is twice stratification height), typical stratified flow behavior is observed, such as reduced decay of kinetic energy and inhibited vertical motion. In contrast, when ξ > 2, a transition occurs and the flow demonstrates non-stratified qualities, including rapid decay of kinetic energy and minimal inhibition of vertical motion. In addition, a method for calculating available potential energy in non-uniform density stratified flows has been developed. It will be shown that mixing of available potential energy χ is confined to the stratification layer, which supports the observation of large mixing in regions of salt fingering found by St. Laurent and Schmitt [1999] and Schmitt [2003].

Indexing (details)


Subject
Physical oceanography;
Mechanical engineering
Classification
0415: Physical oceanography
0548: Mechanical engineering
Identifier / keyword
Applied sciences; Earth sciences; Stratified flows; Thermohaline stratification; Turbulent mixing
Title
Turbulent mixing in stably stratified flows
Author
Hebert, David A.
Number of pages
143
Publication year
2007
Degree date
2007
School code
0118
Source
DAI-B 68/12, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9780549399995
Advisor
Kops, Stephen M. de Bruyn
University/institution
University of Massachusetts Amherst
Department
Mechanical Engineering
University location
United States -- Massachusetts
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3295117
ProQuest document ID
304845215
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/304845215
Access the complete full text

You can get the full text of this document if it is part of your institution's ProQuest subscription.

Try one of the following:

  • Connect to ProQuest through your library network and search for the document from there.
  • Request the document from your library.
  • Go to the ProQuest login page and enter a ProQuest or My Research username / password.