The Study For Aerodynamic And Wake Characteristics Of Floating Wind Turbine

At present,offshore wind turbine is developing from offshore to deep offshore,and its support form has also shifted from fixed foundations to floating platforms.Unlike stationary wind turbines,floating wind turbines can produce complex multi-degree of freedom motion under the action of waves.These movements change the interaction between the blades and the incoming flow,resulting in the aerodynamic performance and wake structure of the floating wind turbine is different from that of the stationary wind turbine.At present,the main research focuses on the causes of aerodynamic performance changes of floating wind turbines and the physical flow phenomena of the near wake field,but there are relatively few studies on the near wake turbulence,vortex band evolution and far wake characteristics of floating wind turbines in real wind and wave environment.Therefore,this paper adopts the Computational Fluid Dynamics(CFD)numerical simulation method to study the aerodynamic and wake characteristics of a floating wind turbine in a wind-wave coupling field.The influences of wave and turbulent wind on the aerodynamic performance and wake structure of the floating wind turbine are systematically analyzed.The research work of this article mainly focuses on the following aspects:(1)The development status of the research field of aerodynamic and wake characteristics of floating wind turbines is described,and the research direction,innovation point and main work of this paper are introduced.(2)The basic theory of aerodynamic and hydrodynamic coupling simulation of floating wind turbine are introduced,including the basic concept and method of floating wind turbine system.The key methods of computational fluid dynamics used in this paper are introduced in detail,which provides theoretical support for the following analysis of aerodynamic performance and wake structure.(3)A numerical model for unsteady flow analysis of horizontal axis wind turbines based on IDDES turbulence model and overlapping grid technology was established to study the blade tower interference effect of wind turbines and the influence of turbulent wind on wind turbine aerodynamics and wake.Research has found that the impact of towers on the aerodynamic performance of wind turbines becomes more pronounced with the increase of wind speed;Under the influence of blades,sudden changes in surface pressure on the tower can cause the tower to withstand unsteady loads;Although high intensity environmental turbulence can affect the stability of the wind turbine output,it can increase the power output of the wind turbine;At the same time,higher turbulence intensity can accelerate the recovery process of wake velocity,but the momentum in the wake recovers faster,bringing greater unstable loads to downstream wind turbines.(4)A numerical model for the aerodynamic and hydrodynamic coupling simulation of OC3-Spar floating wind turbine was established.The characteristics of the output power and thrust of the wind turbine,the variation law of blade surface pressure,the interaction between wind turbine,wave and wake and the evolution law of wake structure were analyzed under the pitch motion of wave action at different periods and heights.It is found that the amplitude of pitch response of floating platform changes obviously with the change of wave period and wave height.Larger wave period can increase the output power of wind turbine and accelerate the development process of vortex structure in the far wake region.The local acceleration phenomenon caused by larger wave height is more obvious,which significantly changes the evolution law of wake structure.(5)The aerodynamic characteristics and far-wake structure of the floating wind turbine in turbulent environment are systematically studied.The output power,thrust,instantaneous aerodynamic load on blades and blade surface pressure distribution as well as the velocity,vorticity and vortex structure distribution in wake area are compared in detail under different turbulence intensities.The results show that the ambient turbulence has a significant effect on the aerodynamic performance and wake structure of the turbine.Higher turbulence intensity will reduce the service life of blades,break the original development trend of wake flow,reduce the area of the region with higher vorticity intensity in wake region,promote the mixing of small-scale turbulence structure in wind turbine wake region and turbulence structure in free flow region,and change the failure mechanism of wake structure.The research in this paper will help understanding the aerodynamic and far wake characteristics of floating wind turbines in real atmospheric environment,and provide guidance for the design of floating wind turbines and the layout optimization of wind farms.