Minh Thao Nguyen: Analysis of Characteristics of Vertical-Axis Turbines Using Computational Fluid Dynamics

Abstract

This thesis presents numerical analyses of straight-bladed vertical-axis turbines with respect to turbine performances and dynamic structural forces. To deepen understanding of the turbine operation and productivity, the effects of geometric parameters and operating conditions on turbine outcomes are essential to be investigated. 

The turbine configurations are modelled by using two-dimensional computational fluid dynamics (CFD) simulations. The CFD models are verified through grid and time-step independence studies, and are further validated against field experimental data for both the vertical-axis wind and marine current turbines. Overall, the numerical results show a reasonably good agreement with experimental measurements, particularly at medium-to-high tip-speed ratios. 

Once the turbine models are validated, the unsteady structural forces of a 12 kW wind turbine are first examined under varying wind speeds and tip-speed ratios. Effects of these operating conditions on the aerodynamic forces are analyzed, and the normal force distributions are compared with open-field measurements to identify physically relevant phenomena during the turbine rotation. This is considered a key contribution of the study, as the scarcity of detailed experimental data of the wind turbine forces often limits the reliability of numerical investigations. Second, a comprehensive analysis is performed on a 7.5 kW marine current turbine to evaluate the influences of different fixed blade-pitch angles. Determining optimal pitch angles is shown to be a critical factor in the development and design of the water turbines. Finally, the combined effects of geometric and operational parameters, including the number of blades, turbine radius, chord length, tip-speed ratio, incoming flow velocity, and Reynolds number, are assessed for hydrokinetic rotors performances. 

Collectively, the findings from the aforementioned studies provide valuable insights into the impacts of the design and operational factors on the turbine power extraction and dynamic loading characteristics, thereby forming a solid basis for the optimization of the vertical-axis turbine designs in both the wind and marine current applications.