EXPERIMENTAL OBSERVATIONS ON EFFICIENCY DIFFERENCE BETWEEN HELICAL AND STRAIGHT BLADED VERTICAL AXIS WIND TURBINES

Abstract

While in operation, the straight bladed vertical axis wind turbines (VAWTs) are affected by the variations in loadings that result in torque and power oscillations. This problem is considered to be solved by adopting helical blades. However, the way this solution affects the turbine’s efficiency is not entirely clear thus this aspect was studied and the results are presented in this paper. Four small scale VAWTs were investigated. A set consisting of one straight bladed turbine and one helical bladed turbine was tested. The airfoil used for this case was the symmetrical NACA 0018. Except for the helical angle, the two turbines were defined by the same key parameters that refer to the: swept area, aspect ratio, solidity, chord length, number of blades, airfoil type and pitch angle. The results revealed that the helical turbine was more efficient than the straight bladed one, generating 53% more power at 12 m/s. Another set of helical and straight bladed versions was tested, this time based on the asymmetrical FX 63-137 airfoil camber out mode. Contrary to the first case, here the straight bladed turbine was more efficient than the helical version, generating 2 times more power at 11 and 12 m/s.