Study On Airfoil Optimization And Roughness Sensitivity Of Aerodynamic Characteristics Of Off-grid Small Vertical Axis Wind Turbine

Due to the characteristics of VAWTs such as simple structure,the ability of accepting wind in any direction,convenient installation and maintenance,VAWTs have been taking an irreplaceable point in off-grid power generation scenarios such as urban environment,offshore applications and remote areas.However,the further development of VAWTs limited by the low wind energy utilization rate.Blades,as the most essential wind capture structure of the VAWTs,embrace good aerodynamic characteristics,which are crucial to the improvement of wind energy utilization rate of VAWTs.The CFD numerical calculation method is adopted in this paper.Firstly,based on the Adjoint method,the VAWTs blade airfoil optimization approach was extended,providing a new idea for the optimization of the aerodynamic characteristics of the blade airfoil;Secondly,the influence of surface roughness on the aerodynamic characteristics of the airfoil under different geometric parameters was explored.It provides references for the design of airfoil with low roughness sensitivity and the optimal design of blades to reduce the decrease in wind energy utilization caused by the rough surface of blades in actual service of VAWTs.Finally,the aerodynamics of VAWTs are further improved through the study of calculation domain criteria.The CFD model of characteristic analysis provides a reference for the efficient and accurate analysis of the aerodynamic characteristics of VAWTs.The chief content of the study is as follows:1.Optimization of Airfoil Based on Adjoint MethodIn order to reduce the tedious modeling work of airfoil,the script written in Python language is used to realize the parametric modeling of airfoil by SCDM software.In view of the better performance of Adjiont Method in other fluid optimization problems,NACA0012 airfoil is taken as the research object in this paper.Based on Fluent Adjinot-Solver,with lift coefficient and lift-drag ratio as optimization objectives,the objective function is established by Linear Weighting Method to optimize NACA0012 airfoil.The lift coefficient of the optimized airfoil is increased by 48.43 % and the lift-drag ratio is increased by 47 %,which develops the optimization method’s correctness and provides a new idea for the aerodynamic geometry optimization design of the airfoil.2.Study on roughness sensitivity of aerodynamic characteristics under different airfoil geometric parametersIn view of the decrease of aerodynamic characteristics caused by the rough surface of the blade during the actual operational environment.Firstly,the large-scale airfoil is more sensitive to roughness based on the Thwaites method.Then,taking NACA four-digit digital series airfoil as the research object,the uniform sand roughness model suitable for CFD solution is established,and the range of sensitive roughness of 0.15 m chord-length airfoil is 0to 0.5mm.Lastly,the relative roughness “RRH” is used to effectively characterize the roughness,and the sensitivity of airfoil geometric characteristics to roughness is studied in the range of RRH is 0 to 1/200.The research shows that the larger the airfoil scale is,the more sensitive to roughness is consistent with the theoretical analysis above.The thicker the airfoil,the more sensitive the lift coefficient to roughness,and the less sensitive the drag coefficient.When the airfoil thickness is greater than 0.12 C,the thicker the airfoil,the less sensitive the lift-drag ratio to roughness.The greater the airfoil camber is,the less sensitive the lift coefficient to roughness is.When the airfoil camber is greater than 0,the drag coefficient and lift-drag ratio show that the greater the airfoil camber is,the less sensitive the roughness is.The above conclusions provide a reference for reducing the power drop caused by the rough surface of the blade during the actual service of VAWTs.3.Establishment and Application of CFD Model in Variable Scale Computational DomainWhen setting the computational domain size of the CFD model of VAWTs,only considering the influence of the blocking effect of the small computational domain size on the calculation accuracy and ignoring the large computational domain size will waste computing resources.In this paper,through the CFD numerical simulation of VAWTs under the full size effect of the computational domain,the selection criteria of the import and export size,width size and rotor center size of the computational domain are obtained,which provides the corresponding reference for the research and design of VAWTs.As a result,a distance from the turbine center to the domain inlet and outlet of 10D(D:diameter of the turbine)each,a domain width of 10 D and a diameter of the rotating core of 1.5D are found to be safe choices to minimize the effects of blockage and uncertainty in the boundary conditions on the results.Furtherly,the experimental test platform is built to verify the reliability of the CFD calculation model.The results show that the established CFD model can better predict the aerodynamic performance of VAWTs.The research work of the thesis provide good theoretical support for the aerodynamic optimization design of VAWTs blades and the reduction of wind energy utilization rate caused by roughness in actual service of VAWTs,and also provide a corresponding reference for the establishment of CFD models for efficient and accurate aerodynamic analysis of VAWTs.