A Study On Unsteady Aerodynamic Characteristics Of Airfoil For Horizontal Axis Wind Turbine

The aerodynamic performance of the wind turbine blade is one of the key factors of designing the wind turbine with high performance.For enhancing the design ability of high performance wind turbine,the accurate prediction of the aerodynamic characteristics and effective flow control for wind turbine are two important methods.For aerodynamic prediction,the precision of the airfoil aerodynamical model,especially under unsteady conditions,directly affect the precision of wind turbine aerodynamic prediction.Due to the engineering application requirements,the computional cost of the aerodynamic model is restricted.Thus,the accurate and efficient wind turbine airfoil aerodynamical model could provide a theoretical supprot for the accurate prediction of wind turbine aerodynamic characteristics.On the other hand,a great deal of control methods are used for the demand of output power increasement,noise reduction,fatigue load decrease and so on.So the flow control,one of the main control methods,is valualbe to be studied and applied.Through numerical calculations,the dynamic stall problem on wind turbine is investigated,the mode decomposition method is adopted to analyze the unsteady flow field of wind turbine airfoil.Depending on the numerical computation data,reduced order models are used to establish the unsteady aerodynamic model of the airfoil,which could provide a support for the enhancement of wind turbine design and optimization level.Meanwhile,for flow control problem,the PIV technology is applied to measure the influence of the slotted tip structure to the wind turbine flow field.The flow mechanism of the slotted tip is analysed by the experimental and numerical data which provides theory and data support for the application of this flow control method.Following are the main work and findings of this research thesis:1.Using the transition corrected k-? SST turbulence model and sliding grid technique,numerical simulations of the flowfield around the periodical oscillation S809 airfoil is earried out.The accuracy of the numerical simulation result is validated by comparing the numerical data with the experimental data.Meanwhile,the unsteady flow field under a deep dynamic stall condition is analysed by the numerical simulation results.2.Based on numerical calculation results data,the further research of the flow field under deep dynamic stall condition is studied by both POD and DMD which are two main mode decomposition methods.Depending on the velocity vector and pressure on the airfoil surface of the mode decomposition results,the unsteady flow field characteristic is analysed which provides further data support for investigating the deep dynamic stall.The characteristics of the mode decomposition methods are shown by comparing with the numerical flow field data.3.Using the numerical computation data as samples,three different kinds of reduced order models are put forward for prediction of aerodynamic characteristic parameters under different unsteady conditions.The numerical simulation results are used to reveal that different reduced order models adapt to different type conditions.The high precision characteristics of three reduced order models under their own conditions are shown by comparing with the numerical simulation results.4.In the study of SBRF model,compared with the experimental and numerical simulation results,the prediction results of traditional semi-empirical model are also analyzed to show the capability of high precision and extremum data capture of the SBRF model under deep dynamic stall condition.5.The influence of the wind turbine flow field caused by the slotted tip is measured by the PIV method.Based on the experimental data of original wind turbine,the flow field characteristics of the near wake and the tip vortex characteristics are described.The influence of the flow field and tip vortex caused by the slotted tip 1s obtained by comparing the data of wind turbine with/without slotted tip.Thus,the capability of the slotted tip to improve the near wake flow 1s validated.6.Compared with the Vatlstas vortex core model,the induced swirl velocity of the tip vortex is analysed.The turbulence coefncient of the vortex core model for wind turbine is obtained from the experimental data of the wind turbine without slotted tip.The effect caused by the slotted tip for the turbulence coefficient is shown by the corresponding data of the wind turbine with slotted tip.The flow field of both wind turbines withjwithout slotted tip is also analyzed by the numerical simulation methods.The influence,caused by the slotted tip,of the tip vortex characteristic during its initial stage is described,which reveals the flow mechanism of this kind of flow control method to improve the tip vortex characteristic.