Instability characteristics of a highly separated natural convection flow: Configuration of a tandem of cold and hot horizontally oriented cylinders placed within a cold cubic enclosure

The study numerically investigated the instability characteristics of a 3D highly separated natural convection flow developing within a cold cubic enclosure in the presence of a tandem of hot and cold horizontally aligned cylinders. The immersed boundary (IB) method was utilized to enforce kinematic no-slip and thermal boundary conditions on the surfaces of the two cylinders. The obtained results were based on the analysis of slightly supercritical flows simulated for three different distances between the cylinders and for Rayleigh numbers Ra∝O(10⁶). It was found that the transition to unsteadiness of the flow sets in via the first Hopf bifurcation, which preserves two types of reflectional symmetry with respect to the central cross-section of the cubic enclosure. The impact of the closeness of the cavity boundaries to the cylinder surfaces on the quantitative and qualitative characteristics of the observed instabilities was extensively investigated. The study elucidated the fundamental instability characteristics typical of highly separated thermally driven flows in confined containers in terms of the bifurcation characteristics and the impact of the object orientation and closeness to the container boundaries on preserving the spatio-temporal symmetries of the slightly supercritical flow.