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Description
Wind power is one of the most reliable renewable resources and its global market has been growing exponentially in the last decade. Drag driven vertical axis wind turbines have several attractive attributes but suffer from inferior efficiencies compared to lift driven alternatives. Easy access to the generator and ability to function in poor wind conditions make it perfect to operate in an urban environment. This study will utilize numerical analysis and wind tunnel tests to investigate using deforming flaps to improve efficiency of a spline geometry rotor. Numerical analysis will be performed on a circular Savonius rotor, a spline geometry rotor, and a spline geometry rotor with deforming flaps. 2D computational fluid dynamic analysis will use the k-&epsis; turbulence model in the Fluent solver in ANSYS 16.0. Results will be presented torque coefficients at varying tip speed ratios, assuming design conditions of 7 m/s wind speed and 1 meter rotor height and diameter. A two-way system coupled fluid-structure interaction analysis will be used to calculate the deformation problem. We discover centrifugal force causes a majority of deformation, especially at higher tip speed ratios. Numerical analysis predicts deforming flaps to decrease efficiency compared to the spline geometry. Three rotors are manufactured from fiber glass and tested in the wind tunnel at San Diego State University. Each rotor’s performance is recorded by torque and RPM measurements at 6 m/s, 7m/s, and 9 m/s. High speed imagery was used to guarantee flap deformation as desired. Wind tunnel data confirmed the CFD prediction with the rotor with deforming flaps underperforming its rigid counterpart. However, the deforming rotor showed significant increase in performance at higher wind speeds. With there being more aerodynamic force available at higher wind speeds and lower tip speed ratios, it suggests there could be a benefit from deforming flaps but its requirements for success may be too unrealistic for passive deformation.
