Session DN - Geophysical and Astrophysical Rotating Flows.
ORAL session, Sunday afternoon, November 19
Congressional C-D, Hyatt Regency Capitol Hill
We numerically examine a viscous, rotating (around the vertical axis) fluid when it is forced by a a small-scale, oscillating grid located near the bottom boundary. The flow near the grid is fully 3D, but for Reynolds numbers of order 1000 and Rossby numbers less than unity, at all other locations the flow quickly organizes itself into Taylor columns aligned in the vertical direction. (The numbers are based on the lengths and velocities of the columnar vortices.) The columns are remarkably independent of the way in which the grid is oscillated (horizontally, vertically, etc.). We report on the cascade of energy from the columnar vortices to both larger and smaller scales, the transfer of energy from 3D to 2D motions, and the spatial transfer of energy from the grid into the body of the fluid and into the top boundary layer. We compute the fractions of energy dissipated in the body of the fluid (the usual, viscous dissipation), the top boundary layer (which we identify as the Ekman dissipation) and at the location of the grid itself (which we identify as being due to the immediate transfer of energy to the small, dissipative scales). Our calculations are compared to laboratory experiments, to numerical simulations of inverse cascades in strictly 2D flows, and to theory.