Blade design and performance testing of a small wind turbine rotor for low wind speed applications

Small wind turbines operating at low wind speeds regularly face the problem of poor performance due to laminar separation and laminar separation bubbles on the blades. This is due to the low Reynolds number (Re) resulting from low wind speeds and small rotor size. The use of specially designed low Re airfoils permits start up at lower wind speeds, increasing the startup torque and thus improving the overall performance of the turbine. A new airfoil was designed and the performance of a 2-bladed rotor designed for low Re application fitted to an Air-X marine 400 W wind turbine was tested at a wind speed range of 3–6 m/s. The low Re rotor incorporated taper and twist to the low Re AF300 airfoil section. The pitch of the blades was varied over a range of 15°, 18° and 20° to study the performance and the startup wind speed. It was found that the turbine performed best at 18° pitch angle. On an average, the wind turbine yielded a power coefficient (CP) of 0.255 at a height of 8.22 m at a wind speed of 6 m/s at 18° pitch angle. Maximum CP based on 10 s data at the freestream velocity of 6 m/s was 0.291. The cut-in wind speed based on 10 s averaged data at the optimum pitch angle was 3.24 m/s whereas the instantaneous cut-in wind speed was 2.34 m/s. In comparison with the baseline 3-bladed rotor, the new 2-bladed rotor produced more electrical power at the same freestream velocity.