Internal Waves
(i) Two of the classic solutions for internal wave field generation are for a Gaussian bump and a knife-edge in an infinite depth ocean. Here are two movies of experimental wave fields obtained using the Synthetic Schlieren technique.
Gaussian bump
Knife-edge
The reader is referred to the following reference for the governing non-dimensional parameters: An experimental investigation of internal wave beam generation by two-dimensional topography, T. Peacock, P. Echeverri & N.J. Balmforth, J. Phys. Ocean. pdf
(ii) Part of the experimental work conducted in the PeacockLab
concerns the modeling of internal tidal generation. This is achieved by
oscillating a 2D mountain back and forth in a linearly stratified ambient.
Advanced image processing software is employed to recover the amplitude of
the resulting internal waves, which appear as well-defined beams,
continuously and in real time. Here, we consider a `supercritical' scenario
in which the maximum topographic slope is slightly larger than the beam
slope. The topography (located in the upper right hand corner of the frames
, but not visible in the movie), takes the form of a
Gaussian curve with a total height equal to one-half the channel depth. From
images such as these, we are able to test complementary theoretical models
and thereby estimate the amount of energy that appears in the low vertical
modes. From field measurements, these are known to travel great distances
from the generation site and therefore carry the most substantial
`non-local' influence.
In this movie, the frames
correspond to 30 cm (in the horizontal) by 20 cm (in the vertical) in physical space. The plotted quantity is the vertical derivative of the perturbation buoyancy field.
(iii) Here are some pictures from recent cruises.
Flow Separation
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This is a close-up picture of a material separation spike in the rotor-oscillator flow (taken by Matt Weldon). At the base of the dye-free region in the heart of the spike lies the separation point; a marginally-stable fixed point. The physical size of the image is 2 cm x 2 cm.
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Periodic rotor-oscillator flow - This is a movie comparing the predicted separation profile for a periodic rotor-oscillator flow (calculated from numerical simulation data) with the corresponding experimental separation profile (you need Quicktime to play this movie).
Turbulent Mixing
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"Lagrangian skeleton of turbulence" - The red and the blue curves are the stable (repelling material lines) and the unstable (attracting material lines) manifolds respectively for a turbulent flow; they are extracted from the experimentally measured turbulent flow field. Video submission to the Gallery of Fluid Motion, 2007 mov file.
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An MIT-shaped fluid blob getting stretched and folded by the complex tangle present in the turbulent flow featured on MIT's homepage on 30th March, 2007.
MIT press release
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The reader is referred to the following reference for further details: Uncovering the Lagrangian Skeleton of Turbulence, M. Mathur, G. Haller, T. Peacock, J.E. Ruppert-Felsot & H.L. Swinney, Phys.
Rev. Lett. 98, 144502 (2007). pdf
