Interactions of tandem square cylinders at low Reynolds numbers

Two identical square cylinders were installed in tandem in a vertical water tank. The effects of the Reynolds number, spacing ratio and rotation angle of the downstream cylinder on flow characteristic modes, drag coefficients and vortex shedding properties were studied. The particle image velocimetry (PIV) scheme was applied to examine and classify the flow field into three characteristic modes: vortex sheet of the single mode, reattached mode and binary mode. Via topological analysis, the velocity vector field, streamline pattern, and the properties of these flow modes are presented and discussed. In the viscosity-dominant flow field, the Strouhal number decreases as the Reynolds number increases. However, in the inertia-dominant flow field, the Strouhal number increases with the Reynolds numbers and approaches a constant for high Reynolds numbers. The maximum drag coefficient in the vortex sheet of reattached mode is approximately 76% lower than that in the single square cylinder case.