UNSTEADY MIXED CONVECTION ABOUT A ROTATING CIRCULAR-CYLINDER WITH SMALL FLUCTUATIONS IN THE FREE-STREAM VELOCITY

Heat transfer from a rotating circular cylinder immersed in a spatiall y uniform, time-dependent convective environment is investigated numer ically including the effects due to buoyancy force. The flow equations , based on the vorticity and stream function, are solved along with th e energy equation by a hybrid spectral scheme that combines the Fourie r spectral method in the angular direction and a spectral element meth od in the radial direction. Several cases are simulated for Grashof nu mbers up to 2 x 10(4), Reynolds numbers up to 200, and a range of spee d of rotation from -0.5 to +0.5. The results show that vortex shedding is promoted by the cylinder rotation but is vanished by the presence of the buoyancy force. In opposing flows, the counter flow currents ca use a large expansion of the streamlines and isotherms in the directio n normal to the free stream velocity. These changes in the structure o f the flow and the temperature fields greatly modify the heat flux alo ng the surface of the cylinder and consequently, the heat transfer rat e is strongly dependent upon Reynolds number, Grashof number, rotation al speed, and the gravity direction. Effects due to how pulsation are also reflected in the Nusselt number history in the form of periodic o scillations.