In the present study, fluid flow and heat transfer and mass transfer around rotating circular cylinder(s) confined in a channel are studied. In unstedy flow past a circular cylinder, the phenomenon of vortex shedding is observed. Vortex shedding causes flow unsteadiness which enhances mixing of species with different concentrations. In this work, fluid flow and heat transfer around a rotating cylinder confined in a channel are studied. Then mixing of two species induced by one or two rotating cylinders is investigated. Numerical investigation is performed using overset grid method and the influence of variation of Reynolds number, rotational velocity of the cylinders, blockage ratio of the channel and the spacing between cylinders on the structure of flow and vortices and parameters such as drag and lift coefficients, strouhal number, nusselt number and mixing index is studied. Numerical simulations are performed for Reynolds numbers varying from 10 to 500, non dimensional rotational velocities of 0, 1 and 2, blockage ratios of 0.1, 0.3 and 0.5, spacing ratios of 1.7 and 2.5, prandtl numbers of 0.7 and 7 and Schmidth numbers of 1 and 4. In flow past a circular cylinder confined in a channel, the pattern of shed vortices is different from that observed in free stream flow past a cylinder and the vortices behind the cylinder moves criss-cross. the transition from steady flow to unsteady flow is delayed as blockage ratio increases. as blockage ratio increases, Drag coefficient and heat transfer increases and mixing index near the exit of the channel decreases. The vortex shedding from the cylinder enhances mixing of species in channel. The vortex shedding behind the cylinder is weakened by rotation of the cylinder, the vortex shedding is suppressed at certain critical rotational velocity. In flow past two circular cylinders confined in a channel, the structure of flow and vortices and mixing index is strongly dependent on the spacing ratio and the state of cylinders rotation and as the fluctuations of flow increases, mixing of species in channel increases. Keywords : Rotati ng cylinder, Channel, Overset grids, Vortex shedding, Forced convection heat transfer, Mixing.
