Flow-induced forces in the channel flow obstructed by an infinite array of equi-spaced circular cylinders have been numerically studied. An immersed boundary method was employed to facilitate to implement the cylinders on a Cartesian grid system. This flow configuration is relevant to the heat exchangers in which vortex generators play an important role in enhancing the heat-transfer capacity. A parametric study has been carried out to investigate the effects of the gap (G) between the cylinders and the channel wall on flow-induced, forces. The blockage ratio (d/H) and the distance between two neighboring cylinder centers were fixed as 0.2 and 3.33H, respectively, where d and H represent the cylinder diameter and the channel height, respectively. The presence of the circular cylinders arranged periodically in the streamwise direction causes a significant topological change of the flow, leading to a significant change in flow-induced forces and frequency of vortex shedding.