The design and construction of a low speed windmill

Abstract

The performance of a horizontal – axis, low speed and small size windmill for pumping water in rural areas with low wind velocities was studied. 7 types of a simple airfoil section were chosen. The aerodynamic characteristic experiment was performed in a low speed wind tunnel to obtain the values of Cl and Cd of each type of airfoil at low Reynolds numbers about 60,000-80,000 and the results were compared with the airfoil NACA 4418. In order to see the flow patterns around the airfoil, flow visualization experiments were carried out in a smoke wind tunnel and a water channel. Considering the simplification of construction and the results of aerodynamic characteristic experiments, an arched plate airfoil with the axis at the center of the chord length and space between the plate and the axis was selected to make windmill blades. A windmill model of 1.25 m in diameter with 8 blades was constructed from the calculating results which employed data from the wind tunnel experiment. The results of a performance test is as follows. For a low speed windmill, the simple airfoil like an arched plate airfoil, gives reasonably good efficiency . The maximum power coefficient was about 16 % at tip speed ratios of 2.0-2.2 when the wind velocity is 2.4 m/s. There occurred some differences between experimental and calculating results. However, they agreed qualitatively well to each other. Since less number of blades are constructed when compared with the multiblade type windmill, the cost of construction, also both the windmill and the tower, is less.