Publications

Abstract : This paper presents a work aimed to design, fabricate and test a fixed pitch, helical vertical axis wind turbine (VAWT) in a 2x3 ft low speed wind tunnel. Since the performance was not found to be satisfactory, a CFD verification to find the root cause was undertaken. The plausible reasons for performance degradation were inferred. Due to the lack of sufficient design details in literature pertaining to the helical blade, the Simple Blade Element Momentum Theory, based on steady state aerodynamics, was adopted. The maximum dimension of the model such height and a maximum diameter of rotation was set as 180 mm and 160 mm respectively, by considering the wind tunnel constraint. The optimum design wind speed was set to be 3 m/s, by gathering the statistical data observed from weather forecast station. The unavailability of low rpm sensitive generators resulted in the choice of two DC brushless motors, which were only 16-17% efficient as generators and design rpm was set to 1500. An Althus and Wortmann design, FX 66-S-196 V1 [1], was chosen as the airfoil section [2].The blades, three in number, are helically wound from the top to the bottom flat frames with a total twist of 30°. The blade was designed with a cambered airfoil, as opposed to the symmetric ones generally in use .The VAWT was then modelled using Solid Edge V20 and Unigraphics NX. This was followed by fabrication using the SLA (Stereo-lithography) technique with ABS plastic (Acrylonitrile butadiene styrene). In Wind tunnel testing, a high start-up speed of 14.36 m/s and a negligible power generation was observed, demonstrating the high inertia of the set-up. The performance degradation can be attributed to the choice of chord, resultant thickness of the airfoil, and the wake which was not accounted in the simple BEM theory used for the design. The situation demanded a CFD analysis. The CFD analysis in FLUENT 6.3.26 comprised of three phases: 2D analysis of the airfoil, 2D and 3D analysis of the VAWT. The 2D simulation of airfoil showed a major difference in data from those obtained from an airfoil database [1]. The unavailability of experimental data for airfoils at low Reynolds numbers is thus concluded as the first factor for the experimental performance of the designed VAWT. The 2D analysis characterized the wake developed over a range of RPMs. The number of vortices reduced as the RPM was increased; however, the intensity of the low pressure region at the centre showed an increase. The 3D simulation of VAWT showed the change in orientation of lift along the span of the blades over different azimuthal angles of rotation. It was seen that only one blade generated lift at a time, with the other two undergoing dynamic stall, thereby confirming the theory that the airfoil in the upwind condition is responsible for the lift generation and consequent torque production for the turbine. Thus, a fixed pitch, helical VAWT has been designed, modeled, fabricated, wind tunnel-tested, and analysed using CFD. The reasons for performance degradation were discussed.