Performance Assessment of a Multi-Step Oscillating-blade Vertical Wind Turbine

ElSayed ElBeheiry ； Wageeh El-Askary

《International Journal of Energy and Power》 1卷1期 (2012/08) Pp. 18-25

並列摘要

A vertical axis wind turbine like the Savonius turbine can develop relatively high torque at small rotational speeds, but they harness a small fraction of the wind incident upon it. The Savonius rotor rotates by an action of differential drag which makes it less efficient. One idea, which is introduced in this work, is to render a vertical rotor rotates by an absolute positive drag in order to influence significantly the generated torque and power coefficient. So, in this study, a rotor is proposed which comprises four vertically arranged (steps) stages and at each step there are two (flat) rectangular blades aligned at 180-degree angle around a vertical shaft in the same vertical plane. Geometrically, the four vertical planes which enclose the blades in the four steps make a 45 degree-angle with each other, successively, from the topmost step to the bottommost step. A total of eight blades two at each step forms the basic configuration of the rotor. The blades open automatically as a result of the air pressure when they advance into the wind (and hence experience zero negative drag), but close (again automatically) when retreating from the wind, i.e., during the power-harnessing part of the operating cycle. When the flat blade closes it is exactly in a vertical plane receiving air flow and when it opens it is exactly in a horizontal plane not receiving air flow at all. Theoretical and experimental dynamic torque and power harnessing tests were carried out for the 8-blade rotor. But, theoretical predictions were carried out for rotors modified with 4 blades or subsequently 16 blades and having the same height of the 8-blade rotor. Other theoretical predictions were made for the 4- and 16-blade rotors with the overall dimensions of the blade kept constant, i.e., duplication of the number of blades means duplication of the rotor height. The results, in terms of torque and power coefficients, indicate that the proposed type of turbines is very competitive to a Savonius wind turbine. It provides the power coefficient higher than that of the classical Savonius rotor while the Savonius rotor offers larger speed ratios for operation. Also, the Savonius rotor provides its maximum power coefficient, which is lower than that of the proposed rotor, at a higher speed ratio than that of the proposed rotor.

並列關鍵字

Wind Energy ； Oscillating-blade Rotor ； Savonius Turbine ； Multi-Stage Rotor ； Theoretical Analysis ； Experimentation