The interaction of waves with fixed or floating structures involves complex wave radiation, wave diffraction and free surface deformation. In this work, the interaction of waves with a pair of cylinders in tandem arrangement is investigated using a numerical wave tank. The numerical simulation is first validated by comparing numerical results and experimental data for regular wave interaction with a single cylinder. Wave interaction with tandem cylinders is investigated for different center-to-center distances between the cylinders. All the numerical simulations are carried out by the in-house CFD solver naoe-FOAM-SJTU which is developed on the open source platform OpenFOAM. The incompressible unsteady Reynolds averaged Navier-Stokes (URANS) equations are adopted as the governing equations. The volume of fluid (VOF) method is applied to capture the free surface. The surface elevation around the cylinders is probed by a series of wave gauges and analyzed using transfer function. The wave forces of upstream and downstream cylinder are discussed in detail. The wave forces experienced by the tandem cylinders is highly influenced by the distance between the cylinders. The local surface elevation and the scattered wave field around the cylinders are also investigated. The results show that the present CFD solver can be an alternative tool to deal with wave-structure interactions.