Oscillatory compressible thermal convection in vertical and inclined differentially heated cavities

Gradinscak, Tomislav and Lappa, Marcello (2017) Oscillatory compressible thermal convection in vertical and inclined differentially heated cavities. In: 30th Scottish Fluid Mechanics Meeting, 2017-05-19 - 2017-05-19, University of Strathclyde.

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Thermal convection in differentially heated cavities has been a research subject for many decades. Studying the phenomena occurring in convective flows inside closed geometries can provide valuable information on the fundamental mechanisms driving a fluid system from an initially quiescent state up to the onset of turbulence. The path taken by the system during this process is strongly linked to the sequence of bifurcations that it undergoes when the temperature difference is increased. This evolutionary path is extremely sensitive to the physical properties of the fluid. Non‐Boussinesq effects can arise from compressibility and variation of thermal conductivity or viscosity with temperature. Even minute variations in such properties can lead to significant changes in the aforementioned sequence of bifurcations. Here we concentrate on the case of a tall differentially heated cavity (containing air) for which the buoyancy flow is in the so‐called boundary‐layer regime (thermal boundary layers located in proximity to the vertical walls and vertical stratification in the center). By using a numerical method able to account for compressibility and variable viscosity effects (implemented in the framework of the open‐source platform OpenFoam), we investigate the response of such a system to the application of temperature gradients able to produce oscillatory flow. The problem is examined by allowing both the Rayleigh number and the inclination (θ) of this configuration with respect to the vertical direction to change (1.9x105≤Ra≤3x105, 0≤θ≤90°). Insights into the role played by compressibility and variable viscosity effects are obtained by comparing the numerical results provided by the variable‐properties model and other simulations based on the classical Boussinesq approximation (with constant fluid properties). The possibility to apply this approach to more complex configurations, such as high‐power plants for the production of energy, is also discussed to a certain extent.