The fluctuating aerodynamic forces and characteristics of flow over two circular cylinders in tandem arrangement placed in a uniform flow are experimentally investigated for the range of spacing ratio of 0.10 to 3.2, at a Reynolds number of 6.5×10^4. Two peaks in the distribution of fluctuating aerodynamic forces on the downstream cylinder are observed when the downstream cylinder is placed before the critical spacing. The maximum values of fluctuating lift and drag forces on the downstream cylinder are 2.0 and 2.8 times that of a single cylinder and it occurs at a spacing ratio of 1.4. The fluctuating fluid forces on the downstream cylinder are very sensitively related with the reattachment position of shear layer separated from the upstream cylinder and the fluctuating fluid forces become maximum when the attachment position, θ, of shear layer reaches to minimum.
