In this work, the flow inside a buoyant cylindrical annuli is investigated using the dual-mesh hybrid RANS-LES approach. This flow is driven by the temperature difference between the inner and outer cylinders. In the dual-mesh approach, an unsteady RANS and an underresolved LES are run simultaneously on two different grids. At every location, the less accurate simulation is corrected towards the more accurate one. A comparison of the dual-mesh results with the results of the standalone simulations is presented to show that the hybrid approach can yield results that are more accurate than the results of the standalone RANS and LES simulations.