ON THE VORTEX SHEDDING MECHANISM BEHIND A CIRCULAR CYLINDER SUBJECTED TO CROSS BUOYANCY AT LOW REYNOLDS NUMBERS

The paper discusses the influences of thermal buoyancy on the vortex shedding mechanisms behind a heated circular cylinder in an infinite medium for cross flow at low Reynolds numbers. The major contribution is the quantification and assessment of the characteristic behavior of the critical buoyancy parameter (Richardson number) for transition from steady to unsteady periodic flow. A two-dimensional numerical simulation is performed in this regard by using a finite volume method based on the PISO (pressure-implicit with splitting of operators) algorithm in a collocated grid system. The range of Reynolds number is chosen to be 10-45. In this range the flow field is found to be steady and separated without the superimposed thermal buoyancy (i.e., for pure forced convection). However, as the intensity of buoyancy increases (i.e., Richardson number > 0), the flow becomes unstable and eventually, at some critical value of the Richardson number, periodic vortex shedding is observed to characterize the flow and thermal fields. The effects of superimposed thermal buoyancy are studied for the Richardson number range 0-2. The critical Richardson number for the onset of vortex shedding is found to decrease (which is in clear contrast with other findings) and the dimensionless frequency of vortex shedding (Strouhal number) is found to increase with Reynolds number in the chosen range.