Numerical and experimental studies of a small vertical-axis wind turbine with variable-pitch straight blades

Abstract

This thesis presents numerical simulations and experiments on the effect of the variable pitch angle of blade rotor on the performance of small vertical-axis wind turbines (Darrieus and Orthopter wind turbine). The power, torque, and flow around blade rotor of VAWTS were analyzed by two-dimensional unsteady computational fluid dynamics simulations using ANSYS Fluent 13.0 program. The Darrieus rotor was composed using three NACA0018 airfoil straight blades. Three different rotor blade configurations were employed which i.e., a fixed-pitch blade with a pitch angle, variable blade pitch angle. The Orthopter rotor blades rotate movement around its own axis a half relative to the main rotor in one revolution. The configurations of different aspect ratio and number of blade (of the Orthopter rotor blade were employed. The effects of the variable-pitch angle, tip speed ratio, and three turbulent models, i.e., the RNG k-e, Realizable k-e, and SST k-ω turbulent models, on the performance of Darrieus wind turbine were investigated. The effect of number of blades, tip speed ratio, and aspect ratio of the Orthopter wind turbine with flat-plate blades rotor were also investigated by numerical simulation using RNG k-e turbulent model. The result predictions of numerical were validated by open circuit wind tunnel experimental data. The numerical simulations results of both a VAWT with variable pitch blade and the orthopter wind turbine had good qualitative agreement with the experiments results. The predictions of performance of using the RNG k-e turbulence model were very close with experimental data. The VAWT with variable-pitch blades has better performance than a VAWT with fixed-pitch blades and by RNG k-e and SST k-ω turbulent models, its can suppress the occurrence of a vortex on its blades at a low tip speed ratio. The performance of the Orthopter is influenced by aspect ratio, number of blade, and tip speed ratio. The highest performance of Orthopter wind turbine at AR=1. The high tip speed ratio lead to reducing torque generation especially at downstream area. The simulations show effects of number of blade on the performance. The high number of blade reduces torque generation of one blade. However, the overall of performance was increased.