The role of cross thermal buoyancy on flow transition around side-by-side cylinders at low Reynolds numbers

We investigate the influence of cross thermal buoyancy to initiate the vortex shedding process around two side-by-side circular cylinders kept in a free stream flow. The critical buoyancy parameter is assessed for the Reynolds number in the range 10–40. In the stated range, a steady separated flow evolves under the pure forced convective condition. However, with the introduction of thermal buoyancy, instability grows and at a specific value of the buoyancy parameter, the flow turns into unsteady periodic with the formation of vortex shedding. The above phenomena have been examined numerically by a two dimensional simulation based on a finite volume method for a fixed gap spacing between the cylinders and considering air as the working medium. It is observed that the strength of the buoyancy could be a decisive factor in demarcating various flow regimes. The critical strengths of buoyancy where the flow transforms into unsteady periodic from the steady pattern are estimated for the Reynolds number range. It shows a decreasing pattern with increasing Reynolds number. The flow transition is visualized through the vorticity, isotherm contours, lift signals and phase diagrams. Furthermore, a regime diagram is constructed to clearly depict various zones of hydrodynamic behavior.