Darrieus wind turbines (DWT) are preferable type of Vertical axis wind turbines at domestic zones that characterized by low wind speed, but low performance is obtained compared quantitatively to other categories of wind turbines. The current study introduces the effect of varying the angles of directed guide vanes (DGVs) on the performance of Darrieus rotor. For this purpose, the experiment test is carried out to determine the highest power coefficient. The numerical model is simulated using three different straight-bladed Darrieus rotor via two-dimensional (2D) computational fluid dynamics (CFD). A grid and mesh independency test as well as the effect of domain size, are conducted and a suitable agreement is obtained. The directed guide vane augmented with the rotor is simulated for two angles of the DGV at different five tip speed ratios (TSR), to investigate the impact of guide vanes angles on the VAWT performance. The results of the present study indicated that output power of the VAWT with a = 20 and b = 55 DGV guide vanes, was improved 16.9%, 38.8%, 42.2%, 27.4% and 27.7%, respectively in four different TSR including 3, 4, 5, 6 and 7.