Numerical Simulation Of Offshore Floating Wind Turbine

With the increasing depletion of traditional energy sources,recent years have witnessed renewable energy,particularly wind energy,raised more and more attention in the world.Offshore floating wind turbine is a new type of development and utilization of wind energy which enjoys certain economics and efficiency in deep-sea areas.Compared to fixed wind turbine,offshore floating wind turbines operate with more complex dynamic characteristics.Economy and security of offshore floating wind turbines can be improved by developing numerical simulation of offshore floating wind turbines and analyzing its dynamic characteristics.In this work,a numerical simulation tool for wind turbine based on vortex lattice method and straight-line segmentation is established to simulate its dynamic performance.The lifting line model is used to simulate the aerodynamic characteristics of the blade surface,and the induced velocity field is solved by Biot-Savart's law.The vortex core model and the “cutoff” treatment are respectively used to introduce the viscous effect and eliminate the numerical singularity.The iterative solution of wind turbine wake field is solved by different numerical algorithms,and a set of time step free vortex wake calculation process is established.The "NREL Phase VI" and "NREL 5MW Baseline" wind turbines are set as the models.The dynamic results in steady state simulation meets well with the experiment's results and the FAST results.Based on this,the influence of different numerical algorithms and induced velocity on the wake field of the wind turbine is discussed.The results show that the algorithm will influence the stability of the wake field structure of the wind turbine,while the induced velocity term has a great impact on its aerodynamics.By combining the classical potential flow theory in hydrodynamics with free vortex method,the "hydro-aero" coupling calculation method for floating wind turbine is established,and the aerodynamic performance and wake field structure of the wind turbine under wind,wave and flow conditions are successfully obtained.To make simulation and stability assessment of the curved filament correction in simulation of fixed and floating wind turbine,it is added to the free vortex method.The analysis starts from the vortex ring,extending to the "hydro-aero" coupling calculation of the floating wind turbine after the gust model is introduced.What's more,to study the effectiveness of the curved vortex correction in oblique flow simulation,the model of extreme wind change is used.The results show that the curved vortex correction may increase the stability of the wake field,although limited by certain theoretical conditions.Also,quantitative analysis of the unsteady aerodynamic characteristics of the blades is carried out by reduced frequency.The contribution of different external loads to the wind turbine reduction frequency is observed in the simulation.