Influence of heat transfers at the free surface of a thermally-driven rotating annulus
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Differentially heated rotating annulus experiments are known to be able to mimic, at a laboratory scale, baroclinic waves related to the synoptic-scale perturbations in the mid-latitude atmosphere. Recently conducted experiments showed that the use of cavities with a shallow fluid depth seems to be able to reproduce some specific phenomena like inertia-gravity waves emission [Hien et al.,JFM,2018]. The choice of experimental design with a large free surface leads to a more intense interaction between the free surface and its surrounding environment. Here we raise the issue on the impact of the free surface on the dynamics of the baroclinic flow. In particular, we focus on the influence of free surface heat transfers on the shallow baroclinic cavity considered in the paper of [Rodda et al., Exp. in Fluids, 2020]. Newton's law is used to model the heat transfer, introducing two parameters: the heat exchange coefficient and the ambient temperature. Using Direct Numerical Simulation [Abide et al.,Comp. and Fluid, 2018], we highlight the influence of the ambient temperature on the flow dynamics in the form of two mechanisms. First, we found that a sufficiently high surrounding temperature leads to the suppression of baroclinic waves. Second, we observed that an ambient temperature lower than the average temperature of the cavity leads to the production of small fluctuations near the free surface.