Most of the wind turbine studies are focused on performance prediction. This study investigates aerodynamic performance of a straight-bladed vertical axis wind turbine for different solidity values and for different airfoil types. For numerical calculations unsteady Navier-Stokes (URANS) equations were solved by ANSYS Fluent 18.2 and Double Multiple Stream Tube (DMST) model was solved by using MATLAB software. Numerical calculation results are compared with experimental data, and the results show that the calculations are valid. Effect of chord length and rotor radius on maximum power coefficient (C-p) point were obtained. According to the Computational Fluid Dynamics (CFD) results maximum moment coefficient (C-m) were obtained at 70 degrees-190 degrees-310 degrees azimuthal angle (theta) of the rotor.