The number of wind turbines that have been deployed all over the world has increased considerably in recent years. Most of the wind turbines that are currently deployed around the globe feature a horizontal-axis configuration. In recent years, there has been a resurgence of interest in vertical-axis wind turbines, however. Vertical-axis wind turbines offer several advantages over turbines with a horizontal-axis configuration. The gearbox and the generator of a vertical-axis turbine can be situated on the ground, thereby reducing the loads on the tower and facilitating the maintenance of the system. In addition, vertical-axis turbines are, by design insensitive to the wind direction and therefore do not require a yaw control system. The main aim of this study is to simulate a helically vertical axis wind turbine using Reynolds-averaged Navier–Stokes equations (RANS) method in order to obtain the performance curves and to get the optimal tip speed ratio. For this purpose, at first, statistical analysis and estimation of wind energy potential in the years 2005 to 2010 in Isfahan was performed. Then, considering the turbine geometrical characteristics such as size, number of blades and type of airfoil, a three- dimensional model of the turbine blades was prepared with the Solidwork software. In order to meshing and to define the solution domain, ANSYS Meshing (ICEM) software was used. In addition, the independency of the results to mesh size was also investigated and eventually the calculation region is divided into about 14,500,000 grids. Finally, the turbine was simulated and analyzed by the ANSYS CFX software using the SST turbulence model. The aerodynamic power, torque and power coefficie nt curves are the most important performance curves for the turbine that were obtained from numerical solution. In order to better understanding the physics of the flow in the solution domain, the contours of velocity and pressure, the streamlines and the vorticity field were also obtained. The power coefficient through the whole revolution of the rotor was obtained, as well. Due to uniform distribution of angle of attack on the turbine blades, the fluctuation of power coefficient through the whole revolution of the rotor was negligible. The results showed that depending on the wind velocity, the maximum power is attained at special tip speed ratio (optimum tip speed ratio). According to the performance curves, the optimum tip speed ratios for three wind velocities 5m/s, 10m/s and 14m/s were obtained as 2.1, 2.2 and 2.45 respectively. The power decreased afterward by increasing the rotational speed of the rotor. The reason is due to the fact that by increasing the angle of attack, the flow separation and the dynamic stall are occurred and the lift force is decreased. The results were validated by experimental data and good agreement obtained. Keywords:Helically vertical axis wind turbine, Numerical Simulation, SST turbulence model, Tip speed ratio, Power coefficient, Torque.
