Effects of end plates with various shapes and sizes on helical Savonius wind turbines

• Aerodynamic performances of helical Savonius wind turbines are investigated.
• Four different helical Savonius wind turbines were tested using subsonic wind tunnel.
• The adapted Maskell's blockage correction method for straight Savonius wind turbine was used to helical Savonius.
• The maximum power coefficient linearly increases with the end plate area ratio up to 1.0.
• The circular end plate is the best choice to maximize the power for helical Savonius.

We experimentally studied the effects of end plates with various shapes and sizes on the aerodynamic performance of helical Savonius wind turbines with twist angles of 180° and two semicircular buckets. To apply the blockage correction method and investigate the effect of end plate, four different helical Savonius wind turbines were tested at a subsonic open-circuit type wind tunnel. The adapted Maskell's blockage correction method suggested by Alexander was adopted for the wind turbine model installed in a closed test section of the subsonic wind tunnel. In order to clarify the end plate effect, power and torque coefficients were measured with various end plate shapes and areas. The use of both upper and lower end plates significantly increases the power coefficient by 36% compared with no end plates. We found that the Maskell's blockage correction method for straight Savonius wind turbines is applicable to helical Savonius wind turbines for small blockage ratios ranging from 3 to 8.3%. It was also observed that the power coefficient increases linearly in proportion to the area of the end plate.