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Physical Society Colloquium
Professor Walter Goldburg
Department of Physics and Astronomy It is possible to make a rapidly flowing sheet of soap film and to create turbulence in the film plane. True, the turbulence generates thickness variations in the film, indicating that it is not strictly two dimensional. However, we will see that this effect does not really destroy the two dimensional (2D) nature of the flow; rather it enables one to visualize the flow field by fast photography Why study 2D turbulence at all? On the practical side, the envelope of air surrounding the earth is almost a 2D sheet, as far as large storms are concerned. On the fundamental side, there are two quadratic invariants for 2D (inviscid) flows, namely the mean kinetic energy per unit mass (as in 3D) and the mean square vorticity density as well. This second conservation law makes 2D turbulence fundamentally different from its 3D counterpart, as will be discussed. Measurements will be presented and where possible, contact will be made with existing theories and speculations.
Friday, March 5th 1999, 15:30 |