  Computational fluid dynamics (CFD) studies are carried out on a two-bladed
vertical axis wind turbine (VAWT) operating at a wind speed of 8 m/s for the
tip speed ratios ($\lambda$) of 0.50 - 3.0. The blade consists of the NACA 0021
airfoil with the chord length of 0.265 m and a rotor radius of 1 m. Basic
sensitivity studies for various time step sizes are carried out. The results
are validated against available measurement data from literature. An excellent
agreement is obtained for small $\lambda$ up to optimum condition. For the
higher tip speed ratios, the two dimensional CFD computations predict higher
results than the wind tunnel experiment, but they are very similar to the field
measurement data. Wake characteristics are presented in the present studies,
showing that the wake becomes Gaussian at 5 times radius downsteam of the
rotor. It is shown that complex flow phenomena occur due to dynamic stall onset
especially for the smaller tip speed ratio.
