Currently, the wind-power market is dominated by Horizontal Axis Wind Turbines (HAWT) owing to their high efficiency. Vertical Axis Wind Turbines (VAWT) are far behind in popularity. However, the interest for future applications of vertical axis wind rotors is increasing because of the simple geometry, low cost, low sensitivity to turbulent flow conditions and simple and affordable maintenance. Thus, an improvement in the efficiency of vertical rotors could close the existing gap and make HAWT more attractive as wind energy conversion devices. In this paper, a new blade spline concept of Savonius rotor with flexible blades is studied experimentally. The idea is to check the performance improvements previously achieved by computational CFD simulations. Two Savonius rotors were built using fiber glass: a rigid rotor with a spline blade shape and a flexible one with the same blade shape but with a morphing section located at the blade’s tips. Important improvements were registered using the flexible rotor compared to the same but rigid rotor, in a large working conditions range, validating the CFD simulation results. The low speed wind tunnel at San Diego State University was utilized for the tests considering a wind speed in the range of 3.5 to 9.5 m/s. A combined analysis of performance and flexibility was also performed to find the deformation associated with the best performance for this kind of rotor. Finally, a comparison was made between the energy conversion of the rigid and flexible rotors at low wind speed for a possible urban application. Results show a 50% power coefficient improvement for the flexible rotor compared to the rigid one at the most optimum working condition. A 90% increase of energy produced by the flexible rotor during one year in the city of San Diego was calculated. Eventually the most productive wind speed for the flexible rotor was found to be 9m/s. Thus, the deformation angle obtained at that value (22°- 32°) was considered as the best deformation for this kind of rotor.
Experimental analysis of a novel Savonius based spline geometry with flexible blades for Vertical Axis Wind Turbines (VAWT)
DANIELI, PIERO
;Lazzaretto A.
2017
Abstract
Currently, the wind-power market is dominated by Horizontal Axis Wind Turbines (HAWT) owing to their high efficiency. Vertical Axis Wind Turbines (VAWT) are far behind in popularity. However, the interest for future applications of vertical axis wind rotors is increasing because of the simple geometry, low cost, low sensitivity to turbulent flow conditions and simple and affordable maintenance. Thus, an improvement in the efficiency of vertical rotors could close the existing gap and make HAWT more attractive as wind energy conversion devices. In this paper, a new blade spline concept of Savonius rotor with flexible blades is studied experimentally. The idea is to check the performance improvements previously achieved by computational CFD simulations. Two Savonius rotors were built using fiber glass: a rigid rotor with a spline blade shape and a flexible one with the same blade shape but with a morphing section located at the blade’s tips. Important improvements were registered using the flexible rotor compared to the same but rigid rotor, in a large working conditions range, validating the CFD simulation results. The low speed wind tunnel at San Diego State University was utilized for the tests considering a wind speed in the range of 3.5 to 9.5 m/s. A combined analysis of performance and flexibility was also performed to find the deformation associated with the best performance for this kind of rotor. Finally, a comparison was made between the energy conversion of the rigid and flexible rotors at low wind speed for a possible urban application. Results show a 50% power coefficient improvement for the flexible rotor compared to the rigid one at the most optimum working condition. A 90% increase of energy produced by the flexible rotor during one year in the city of San Diego was calculated. Eventually the most productive wind speed for the flexible rotor was found to be 9m/s. Thus, the deformation angle obtained at that value (22°- 32°) was considered as the best deformation for this kind of rotor.
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