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The large-scale flows of the oceans and the atmosphere are driven by a non-uniform surface heating over latitude, and rotation. For many years scientists try to understand these flows by doing laboratory experiments. In the present paper we discuss two rather new laboratory experiments designed to study certain aspects of the atmospheric circulation. One of the experiments, the differentially heated rotating annulus at the Brandenburg University of Technology (BTU) Cottbus, has a cooled inner cylinder and a heated outer wall. However, the structure of the atmospheric meridional circulation motivates a variation of this "classical" design. In the second experiment described, operational at the Institute of Continuous Media Mechanics (ICMM) in Perm, heating and cooling is performed at different vertical levels that resembles more the atmospheric situation. Recent results of both experiments are presented and discussed. Differences and consistencies are highlighted. Though many issues are still open we conclude that both setups have their merits. The variation with heating and cooling at different levels might be more suited to study processes in the transition zone between pure rotating convection and the zone of westerly winds. On the other hand, the simpler boundary conditions of the BTU experiment make this experiment easier to control. [ABSTRACT FROM AUTHOR]

To a better understanding of buoyancy-driven flows in enclosed tall cavity, Large Eddy Simulations are performed with an original solver, which combines fourth-order compact scheme and parallel computing. The direct numerical simulation of the natural convection flow between two heated parallel plates are provided to validate the present numerical method. Then, the mean and turbulent statistics of the buoyancy-driven in a tall cavity at the moderate Rayleigh number are computed. The results of the vertical configuration flow are successfully compared with the available experimental data. Then, the statistics are discussed with respect to the inclination angle of the tall cavity. Especially, the occurrence of convection rolls in the cavity inclined to the horizontal is shown, as well as their roles in the deterioration of the thermal stratification. [ABSTRACT FROM AUTHOR]

The finite difference preconditioning for higher-order compact scheme discretizations of non separable Poisson's equation is investigated. An eigenvalue analysis of a one-dimensional problem is detailed for compact schemes up to the tenth-order. The analysis concludes that the spectrum is bounded irrespective of the mesh size and the continuous variable coefficient. Hence, combined to a multigrid method, the preconditioned Richardson method shows a convergence rate which is independent from the mesh size and the variable coefficient. Several numerical experiments, including the simulation of a flow with large density variations, confirm that the spectrum of the preconditioned operator remains bounded. [ABSTRACT FROM AUTHOR]