Georgios Matheou &
Daniel Chung
Jet Propulsion Laboratory
California Institute of Technology
Pasadena, California

Direct numerical simulation of stratified turbulence. Lighter colors correspond to denser fluid.

Stably stratified flows – instances where a light fluid is on top of a heavier fluid – are prominent in many geophysical and engineering systems. These two images are taken from a series of simulations that aim at improving our understanding of the dynamics of turbulence in a stably stratified fluid. The simulations shed light on the competition that is taking place between two forces: shear, which occurs when the upper fluid moves faster than the lower one, and which generates turbulence; and stratification, which occurs when the upper fluid is lighter than the lower one, and which tends to inhibit or stabilize part of the turbulent motions. The images detail the structure of density fluctuations (lighter colors correspond to denser fluid) in these two limiting cases.

In the top figure, the stratification is neutral and density behaves like a passive substance exhibiting ramp-and-cliff structures. At the same time, the structures are being sheared, giving rise to forward-leaning structures. As stratification increases, vertical motions are progressively inhibited and eventually turbulence collapses, forming thin layers as shown in the bottom image.

Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center. The authors acknowledge the support provided by the NASA MAP, ONR Marine Meteorology, and NOAA MAPP/CPO programs. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

Related Abstract

  Direct numerical simulation of stationary homogeneous stratified sheared turbulence

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This image can be freely reproduced with the accompanying credit: "Courtesy NASA/JPL-Caltech.".