The study examines the unsteady flow characteristics and aerodynamic interactions of a 2-dimensional circular and a square cylinder arrangement in tandem. These arrangements are crucial for engineering applications like bridge piers, offshore structures, and heat exchangers. Computational fluid dynamics (CFD) simulations are conducted at 20 m/s to analyse the unsteady fluid flow around circular and square cylinders. The effect of the spacing between the cylinders in tandem over the flow unsteadiness has been investigated. The results reveal important attributes of the tandem arrangement, such as wake formation and vortex-shedding phenomena. With the increase in the spacing between the circle and square cylinders in tandem, the development of vortices in the wake of the cylinder is observed. In addition, with an increase in the spacing, the influence of a circular cylinder ahead of the square cylinder is observed. With the increase in the spacing, a positive shift in the frequency as well as an increase in the magnitude of the fluctuation is observed. These findings can guide engineers in optimizing the arrangement to reduce vortex-induced vibrations and improve the overall efficiency and stability of structures subjected to fluid flow.