Experimental investigation and the design analysis a HAWT with circular arc blade section

Abstract

An experimental investigation and design analysis of a horizontal axis wind turbine with circular arc blade section have been performed. An elaborate theoretical analysis of the performance characteristics of the wind turbine using different prediction methods has also been presented.. . Performance of wind turbine models with circular arc blade section for different number of identical blades have been studied at constant wind velocity. The wake velocities at the downstream of one rotor diameter of the wind turbine have also been measured. The theoretical analyses have been done using momentum theory, blade element theory and the cascade theory. The dynamic effect, which developed in the wind turbine blade, has been added to the cascade theory. The effects of coning, tilting, wind shear, hub and tip losses are also included in the study. It is observed that the calculated results of the wind turbine with circular arc blade profile are comparable with those of the turbine with airfoil blade section. The design is based on generating electricity and pumping water for the remote areas of Bangladesh where moderate wind velocity persists. Minimum value of the drag to lift ratio is used in conventional designs, but in the present design the lift value corresponding to the 90% ofthe maximum is used. As the turbine blade rotates continuously, at any local radius of the blade for any particular tip speed ratio the magnitude of the relative flow velocity remains constant but its location and orientation varies continuously and it has been assumed to impart the dynamic effect on the performance of the turbine. An empirical relation is introduced to take into account this dynamic effect. This is developed from the correlation of the experimental results. Design tip speed ratio depends on the number of blades of the wind turbine rotor. An empirical relation between the design tip speed ratio and the number of blades for the wind turbine with circular arc blade section is established. In the present design of the wind turbine having circular arc blade section, the value of the design tip speed ratio is chosen from this relation. The experimental results of the performance of the wind turbine are compared with the calculated results from different theories. It is observed that there are good agreements between the experimental results and the calculated values by the cascade theory incorporating dynamic effect.