Dynamic Modeling and Performance Analysis of Horizontal Axis Wind Turbines: Land-Based and Floating Models

Abstract

In this thesis, the aerodynamic performance of horizontal axis wind turbines were analyzed directly in a series of simulations using computational fluid dynamics and experimental tests using wind tunnels. Two different types of horizontal axis wind turbines were examined involving: land-based and floating models. For land-based wind turbines, the aerodynamic design of a 10 kW wind turbine rotor was initially performed using both ideal and actual rotor theories. The BEM provides a non-linear blade profile in terms of chord and twist distributions. From the technical point of view, linear distributions of the chord and twist angle are highly recommended to enhance the blade aerodynamic performance and ease the fabricating complexity. Hence, a unique optimization approach is introduced to linearize the blade profile by dividing the congruent line of both ideal and actual models into equal divisions. The points along the identical tangent line are considered as floating new blade roots, whereas the blade tip was kept fixed based on the primary design. The linear profile based on the new value of blade root is described using algebraic equations. The local element torque, capacity factor, and the annual energy production based on the Weibull distribution are adopted to evaluate and select the optimal blade profile. The aerodynamic performance and aeroelastic behavior of both primary and linearized blade profiles were analyzed using CFD and FEA approaches respectively. Results show an enhancement in the aerodynamic performance in terms of power coefficient up to (5.9%) compared to the primary blade design. Moreover, the optimized blade has shown less tip deflection by 27.92 % than the primary blade at low wind speed. Since the power production of the wind turbine is proportional to the third order of incoming wind speed, therefore, even a slight increment in wind speed can immensely enhance the overall aerodynamic performance of the wind turbine. Hence, encasing the turbine rotor with a shroud is the most efficient approach used to concentrate and enhance the incoming wind speed through the rotor plane. In this sense, a unique optimization approach is introduced to optimize the geometrical features of the shroud profile including length of both entrance and diffuser sections, radii of both diffuser and entrance area. A high-fidelity CFD simulation is performed to investigate the aerodynamic performance of both bare and shrouded rotors using commercial software STAR CCM+. Furthermore, an open-loop wind tunnel used to experimentally tested both turbine configurations under various environmental conditions. Finally, a systematic comparison of the aerodynamic performance between CFD results and experimental data was implemented for both conventional and shrouded turbines. The optimization findings affirmed that the total length of optimized shroud profile is shorter by approximately 6 % than the baseline (C_ii) configuration. However, the wind speed obtained from the optimized shroud profile shows an improvement of 1.58% compared to the baseline configuration at the throat area. It was observed that the power coefficient obtained from shrouded turbine was increased by approximately 66.4% compared to the conventional wind turbine based on the CFD results, whereas, it was increased by 69.3% according to the experimental data. In case of floating wind turbines, the present work provides upper estimates for power gains or losses due to floating OC4-DeepCWind semi-submersible platform motion. Furthermore, this investigation focusses on determining which degree of platform responses most affects the average power production. In this sense, three degrees of freedom of semi-submersible platform motions (surge, heave, and pitch) are considered and separately investigated using high-fidelity CFD simulation. The Dynamic Fluid Body Interaction (DFBI) and Volume of Fluid (VOF) approaches are employed to accurately capture the aero-hydrodynamic interaction due to the coupled wind-wave loads. Results obtained from the CFD simulation including aerodynamic torque, thrust force, and platform-hydrodynamic responses are well verified and compared with the corresponding data from NREL-FAST and OrcaFlex codes. Moreover, the effect of blade-tower interferences, tension force of the catenary lines, and the complex interactions between the blade tip-vortices and its own wake were investigated and visualized numerically