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Title: BEMT and CFD-based unsteady aerodynamic analyses of floating offshore wind turbine
Author: Lin, Lin
ISNI:       0000 0004 6062 0535
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2016
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Nowadays the demands for floating offshore wind (FOWT) have exceeded 5MW with the rapidly growing wind market. The aerodynamic environment of FOWT is more complex than onshore or fixed offshore wind turbine due to the large motions of floating platforms. The platform motion, especially pitch and surge motions, increase aerodynamic unsteadiness, wake interactions and other complex flow phenomena. These conditions influence the velocities and accelerations at the rotor sections along the blade. However, a limited simulation and load estimation capability make aerodynamic analysis a challenge. It is questionable whether some industry aerodynamic analysis codes like conventional Blade Element Momentum (BEM) theory and Generalised Dynamic Wake theory are accurate. Results indicate that current methods for predicting the aerodynamic loads may be inadequate. Aerodynamic flow effects cannot be accurately modelled using traditional BEM theory with common corrections in such a complex condition. So compared with traditional potential theory, CFD method provides more physically realistic simulation. The applying and validation of CFD method will be outlined in this dissertation. The commercial multi-purpose CFD solver STAR CCM+ 9.02 is employed for calculation of the flow using Reynolds-Average Navier-Stokes (RANS) equations in conjunction with different turbulent models. Finally, results from CFD simulations of various offshore floating wind turbines under different load conditions will be presented. CFD simulation is accurate, but time consuming. So, an optimization method will be detected to get a more accurate result and saving time. 2D CFD RANS data was instead of commonly 2D data. However, not result in the desired improvements when compared to BEM results. Therefore, a 2D airfoil data obtained by post-processing of 3D CFD computations was used. 3D results were used to estimate 2D airfoil characteristics to modify two important parameters in BEM codes: the axial and the tangential induction factors by applying the reduced axial velocity method by getting the local angle of attack from CFD solutions. This thesis will demonstrate that the aerodynamics of offshore floating wind turbines is sufficiently different from conventional offshore and onshore wind turbines, warranting the use of higher fidelity analysis approaches. It is obvious that thexxiiiplatform motions will have a great effect on unsteady aerodynamic performance of the wind turbine rotor. This thesis will study and explain the rules and reasons of this phenomenon in detail. Future offshore floating wind turbine designs should strive to either minimize platform motions or be complementarily optimized, via higher fidelity aerodynamic analysis techniques, to account for them. It is believed that this dissertation is the first in-depth study of offshore floating wind turbine aerodynamics and the applicability of various analysis methods.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral