In this thesis, the Detached Eddy Simulation (DES), available in ANSYS-FLUENT) is employed to solve 2D unsteady flow over double cylinders in tandem for three different pitches and a Reynolds number of 22,000. With proper choice of mesh sizes and time steps, the DES is found to yield accurate results at affordable computing cost. Effects of pitch to diameter ratios on the lift and drag forces in the spatial and temporal domains are investigated. The simulation results are useful in studying cross-flow flow induced vibration of slender structures.