Tuesday, February 28, 2006

Formation of Large Fluid Vortices: Corporate Merger or Hostile-Takeover

Large, energetic vortex structures commonly form in irregular or turbulent two-dimensional flows. Familiar examples are Jupiter's Red Spot or hurricanes and typhoons on Earth. What is
the mechanism that transfers energy from small-scale vortices to these often long-lived, large-scale circulation patterns? Many suggestions have been made, such as a merger of small vortices into larger ones. According to this scenario, the process is similar to
the consolidation or merger of many small corporations into a mega-corporation. In a new paper, researchers verify by experiment and simulation a quite different mechanism based on elongation and thinning of small-scale vortices, stretched like taffy by large-scale strain. This process weakens the velocity of the small vortices and transfers their kinetic energy into the large-scales. The thinning mechanism allows the large vortices to drain the energy of the smaller ones, squeezing them dry. Thus, the process is more like a hostile takeover of many small corporations by a larger one that strips their assets and liquidates them. According to the
authors, the work provides quantitative models of how a population of small-scale vortices sustains on the large-scale circulations. These results will help to model and predict formation of
large-scale vortices in atmospheres and oceans (Chen et al., Physical Review Letters, 3 March 2006; contact Gregory Eyink, Johns Hopkins, image,)

The American Institute of Physics Bulletin of Physics News
Number 767 February 28, 2006 by Phillip F. Schewe, Ben Stein, and
Davide Castelvecchi

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