Effect of cross-stream buoyancy and rotation on the free-stream flow and heat transfer across a cylinder

Cross-stream buoyancy-induced formation of VS (vortex shedding) past a rotating cylinder maintained at constant wall temperature is studied at Re = 40 and 100. The non-dimensional rotational velocity (α) is varied from 0 to 8 and Richardson number from 0 to 1 with air as the working fluid. Semi-explicit finite-volume method code implemented on colocated Cartesian multi-block grid is used. Buoyancy-induced onset of vortex shedding is found for stationary/rotating cylinder at sub-critical Re = 40. Steady-VS flow transition map is shown for the different rotational velocity and Ri; and reasoned using vorticity dynamics. At higher rotational velocity, origin of buoyancy-induced secondary frequency for Re = 40 at α = 6 and for 100 at α = 5 is discussed using spectral analysis and phase portrait technique. The VS frequency is much smaller at higher as compared to lower rotational velocity and increases with increasing Ri. A monotonic increase in the downward lift force and a reversal in the direction of drag force is found with increasing rotational velocity. Rotation can be used as a drag reduction and heat transfer suppression technique.