Numerical Investigation of the Effect of Fixed and Variable Pitch Angle Blade on Dynamic Stall of Flow Field Around Darrieus Wind Turbine Blade

The Darrieus lift-based VAWT has been studied by many scientists due to its simplicity of design and the wind direction independency. Due to increasing angle of attack and dynamic stall at low tip speed ratios, these wind turbines have the inherent problem of self-starting inability and produce less power's compared to that of horizontal axis wind turbines. In this study, the effects of variable blade pitch angle mechanism on decreasing dynamic stall have been investigated. Finally, a pitching system (variable pitch Darrieus-type wind turbine) has been proposed, which can reduce both the blades, oscillating motion and the magnitude of the angle of attack in one revolution, compared to that of conventional VAWT. In this study, unsteady two-dimensional simulation is conducted, using CFD with moving mesh the rotating rotor. Simulation of different preset pitch angles of ±3° and ±6°¬, ±9° and ±12°, it is concluded that adjustment of pitch angle about -3°, causes a delay in flow separation and control dynamic stall. It was also observed that a variable-pitch blade turbine can suppress flow separation on its blades at low tip speed ratios. This leads to delay or elimination of dynamic stall and results in a higher efficiency during the range of turbine operation compared to that of fixed-pitch blade Darrieus turbines.