Approaching the Asymptotic Regime of Rapidly Rotating Convection: Boundary Layers vs Interior Dynamics

Keith Julien
University of Colorado, Boulder

Extensive explorations of low Rossby number - high Rayleigh number convection present a fundamental challenge for both laboratory experiments and DNS. While simulations of asymptotically reduced system of equations valid in the limit of strong rotation
has provided some progress some important discrepancies still remain. In this talk Rapidly rotating Rayleigh-B´enard convection is studied by combining results from direct numerical simulations (DNS), laboratory experiments and asymptotic modeling. The asymptotic theory is shown to provide a good description of the bulk dynamics at low, but finite Rossby number. However, large deviations from the asymptotically predicted heat transfer scaling are found, with laboratory experiments and DNS consistently
yielding much larger Nusselt numbers than expected. These deviations are traced down to dynamically active Ekman boundary layers, which are shown to play an integral part in controlling heat transfer even for Ekman numbers as small as 1e-7. By adding an analytical parameterization of the Ekman transport to simulations using
stress-free boundary conditions, we demonstrate that the heat transfer jumps from values broadly compatible with the asymptotic theory to states of strongly increased heat transfer, in good quantitative agreement with no-slip DNS and compatible with the experimental data. Finally, similarly to non-rotating convection, we find
no single scaling behavior, but instead that multiple well-defined dynamical regimes exist in rapidly-rotating convection systems.

This is joint work with J. Aurnou (UCLA), S. Stellmach (U. Muenster), Eric King (Berkeley),
G Vasil (Sydney) and Edgar Knobloch (Berkeley)

Presentation (PDF File)

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