Dynamics of the Mixed Layers in Stratified Sheared Flows

Abstract

Vast verity of geophysical flows occur in density stratified fluids in a presence of sheared mean velocity profiles. Under such conditions it's been observed that vigorous turbulence leads to generation of mixed layers within the fluid, e.g. the regions of homogeneous density separated from each other by strong density gradients (interfaces). These layers could be of large vertical scales as well as of fine scales. An example of such flows is the destratification of the upper layer of the ocean under the action of the surface wind stress and the formation of multiple mixed layers which are observed within the seasonal thermocline in the ocean as well as in fresh lakes. Such structures in a turbulent flows are thought to play a crucial role in the determining the turbulent fluxes of momentum, buoyancy and other tracers which in turn affect the further dynamics of the flow. Nonetheless, the problem of turbulent transport remains one the most difficult ones in geophysics. In the present study the dynamics of layers is explored within a turbulent fluid in a presence of a sheared mean flow. A set of experiments were performed in which a linearly stratified fluid is driven by the stress applied by a rotating horizontal disk at the surface. This setting leads to the formation of the surface mixed layer extending from the disk into the interior of the fluid. Its evolution with time and its dependence of the stratification and the rotation of the disk are obtained. Furthermore, small scale mixed layers were observed in below the surface mixed layer. They have a complicated dynamics with multiple regimes, which were attempted to characterize. The description of the experiment and the behavior of the observed mixed layers is presented. Further, a phenomenological model is developed that explains the mechanism under which the secondary mixed layers are formed.

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Document Details

Document Type
Technical Report
Publication Date
Oct 18, 2010
Accession Number
ADA557279

Entities

People

  • Georgy Manucharyan

Organizations

  • Woods Hole Oceanographic Institution

Tags

DTIC Thesaurus Topics

  • Buoyancy
  • Demographic Cohorts
  • Dynamics
  • Energy Production
  • Fluid Dynamics
  • Kinetic Energy
  • Layers
  • Mechanical Properties
  • Potential Energy
  • Reynolds Number
  • Richardson Number
  • Steady State
  • Stratified Fluids
  • Stresses
  • Turbulence
  • Turbulent Flow
  • Turbulent Mixing

Fields of Study

  • Physics

Readers

  • Computational Fluid Dynamics (CFD)
  • Ocean-Atmosphere Mesoscale Modeling, Data Assimilation, and Flux Boundary Layers
  • Plasma Physics / Magnetohydrodynamics