Large-eddy simulations were carried out to simulate laboratory-scale isolated buoyant
convection in unstratified water with shelf and slope topography in the presence of
rotation and to compare and complement the experimental study of Jacobs & Ivey
(1998) under the same conditions. The simulation code developed in this work was a
three-dimensional incompressible Navier–Stokes solver and the simulation runs were
performed on a distributed memory massively parallel computer, namely the IBM
SP2, to study the effects of different applied heat fluxes and system rotation rates. We
are able to show for the first time the detailed temporal evolution and spatial structure
of the three-dimensional convective flow field. Rayleigh–Bénard instability in the form
of circular concentric convective rings is recognized in the initiation process of the
convection. The onset of Rayleigh–Bénard instability was investigated and the critical
Rayleigh number was found to increase with Taylor number only when the Taylor
number is greater than 5 × 103, where both non-dimensional parameters are based on
the conductive layer thickness. The horizontally axisymmetric convective rings later
break down and evolve into a quasi-two-dimensional vortex field. An azimuthal rim
current develops around the periphery of the convective region. Our simulation results
confirmed that the rim current velocity scales as Bt1/2/Hf3/2.
Here B is the buoyancy flux applied over a bottom circular disk, f is the Coriolis parameter,
t is the time and H is the distance between the tank bottom and the shelf. With increasing lateral
temperature gradient the rim current undergoes a baroclinic instability. Our study of
root-mean-square velocities in the convective region suggests that the transition from
the buoyancy-flux-controlled to background-rotation-controlled flow occurred when
the natural Rossby number Ro* became smaller than a critical value between 0.015
and 0.044. The simulation results of the convective overturning time, the wavelength
of the baroclinic eddies and the density anomaly at steady state are all in reasonable
agreement with the experimental data.