Numerical Analysis Of Aerodynamic Performance Of Floating Offshore Wind Turbine

This paper reviews the research background of aerodynamic performance of floating offshore wind turbine(FOWT),in terms of research methods,simulation software and research progress.And the basic theory of FOWT concerning aerodynamic simulation is also introduced in this paper.The NREL 5MW wind turbine which is supported by OC3-Hywind Spar floating platform is chosen to conduct simulations in STAR-CCM+ software,including three dimensional aerodynamic simulation of turbine blade,the effect of platform motions on FOWT’s aerodynamic performance and the coupled aero-hydro simulation of Spartype FOWT in wind-wave field.The geometry model of NREL 5MW wind turbine is transformed into the CFD software to build up the numerical model.Based on the k-?(SST)turbulence model,the MRF method and sliding mesh technique are adopted to model the rotation of wind turbine.The grid independence study and the result comparisons between CFD and FAST in various calculation cases are conducted to validate the CFD model.In addition,the impact of vertical wind shear and tower shadow effect are also investigated.Based on the verified model,using the overset mesh technique to model the motions of FOWT,three DOF’s platform motions are simulated to show the aerodynamic effect on OC3-Hywind Spar FOWT independently,including surge,pitch and yaw.The results indicate that surge and pitch motions of floating platform have significant impact on power output of wind turbine,while yaw motion shows less impact on the overall performance.In order to stabilize power output of wind turbine and eliminate the fatigue of wind turbine structures,including tower,blades and reduction gear,it is of great importance to control platform motions reasonably and develop pitch controller system which is applicable for floating wind turbine.Besides,Spar FOWT is adopted to simulate the aerodynamic performance with combined wind-wave loads.The overall numerical model is built up to test the hydrodynamic performance of platform and conduct the coupled aero-hydro simulation in wind-wave filed.The results are shown as below:(1)The curves of power and thrust force fluctuate with 1/3 rotating period of wind turbine in tower shadowing effect,and the tower shadowing effect has less impact on wind turbine performance.(2)The period of platform pitch motion is similar to wave period.When the turbine pitches upwind,the power output and thrust force increase and vise versa.(3)Because of thrust force of the turbine,the equilibrium positions of surge and pitch motion tend to the downwind direction.The wave load has the same magnitude as thrust force,while tower wind forces are much smaller than thrust force.