Influence of counter rotation on fluid flow and heat transfer around tandem circular cylinders at low Reynolds number

Two-dimensional numerical investigations are carried out to understand the effect of rotation on flow characteristics over two identical circular cylinders in an unconfined medium at low Reynolds number. Both the cylinders are placed in tandem arrangement transverse to the incoming flow, and the dimensionless spacing between the cylinders is varied in the range $$0.2 \le g* \le 3.0$$ . Unsteady laminar incompressible flow computations are performed for all spacings using a finite volume technique at constant Reynolds number (Re = 100) and Prandtl number (Pr = 0.71). The upstream and downstream cylinders are made to rotate in the clockwise and counterclockwise directions, respectively. Results show that the counter rotation brings stability in the flow field around the cylinders, which in turn alters the fluid flow and heat transfer characteristics. At some point of the rotation rate, irrespective of the direction of rotation, the flow permutes from unsteady periodic vortex shedding to the steady state. Moreover, the critical rotational speed slightly decreases with gap spacing and shoots up at larger gap spacing.