Experimental and Numerical Investigation of Aerodynamic Performance for Vertical-Axis Wind Turbine Models with Various Blade Designs

The demand for wind energy as a renewable source is rising substantially. A growing interest exists in utilizing potential energy conversion applications in areas with less powerful and less consistent wind conditions. In these areas, vertical-axis wind turbines (VAWTs) possess several advantages over the conventional horizontal-axis type. Savonius turbines are drag-based rotors which operate due to a pressure difference between the advancing and retreating blades. These turbines are simpler in design, less expensive to install, non-dependent of wind direction, and more efficient in lower wind speeds. In the present study, six different rotor designs with equal swept areas are analyzed with wind tunnel testing and numerical simulations. These models include a traditional Savonius with 2 blades, “CC” model, “QM” model, and 90 degree helical twist models with 2, 3, and 4 blades. The models were designed using the CAD software SolidWorks. Due to the complex geometry of the blades, the physical models were then 3D printed for experimental testing. Subsonic, open-type wind tunnel testing was used for measuring RPM and reactional torque over a range of wind speeds. For the numerical approach, ANSYS Fluent simulations were used for analyzing aerodynamic performance by utilizing moving reference frame and sliding mesh model techniques. For the models with helical twist, the cross-sections of the blades varies in the Y-direction. Because of this, a 3-dimensional and transient method was used for accurately solving torque and power coefficients. The 5 new rotor geometries included in the study create a center of pressure further from the axis of rotation causing greater torque on the turbine shaft, compared to the traditional Savonius turbine. The CC and QM cross-sections reduce the total range of negative torque on the blades by 20 degrees, compared to the traditional Savonius model. Helical designs better spread the applied torque over a complete revolution resulting in positive torque over all operational angles. Helical models with 2 and 3 blades have the best self-starting capability in low wind speeds. Under no generator loading, Helical3 begins rotation of 35 RPM at just 1.4 m/s wind velocity. The highest power coefficient in the study is achieved, both experimentally and numerically, by the helical VAWT with 2 blades. Averaged over one full rotation, a maximum power coefficient of 0.14 is observed with the Helical2 model at tip-speed ratio of 0.475