Research On Aerodynamic Performance And Flow Field Characteristics Of H Type Vertical Axis Wind Turbine

In recent years,as people's awareness of environmental protection has increased,more and more attention has been paid to renewable energy sources.Wind energy is a kind of clean,quiet and efficient renewable energy source.The main use form of wind energy is wind power generation,and wind power generation has the most commercialized development prospect and development conditions.The H-type vertical axis wind turbine(H-VAWT)does not need to adjust to the wind and there is no complex yaw device;the transmission system and gear box are placed on the ground,so it is easy to install and maintain;the main shaft and generator of the H-VAWT are not directly connected,so the rotor has good lightning protection;the manufacturing costs of the H-VAWT is low.Due to the above advantages,the H-VAWT is more suitable for wind power generation in urban.However,the angle of attack of the blades of the H-VAWT is constantly changing during the rotation even when the wind speed and rotation speed are kept constant.Therefore,the commonly used NACA symmetrical airfoil of the H-VAWT can no longer meet its requirements for aerodynamic performance.In addition,since H-VAWTs are suitable for installation in urban areas close to the population,therefore it is also crucial to predict their noise levels.Currently,there are few researches on the aerodynamic performance and flow field characteritics of the H-VAWT,optimizing the airfoils which are suitable for the operating conditions of the H-VAWT,and forecasting the aerodynamic noise,which hinders the further development and application of the H-VAWT.Therefore,this article has done the following research on the above issues.1.In view of the fact that the genetic algorithm is prone to "premature" phenomenon in the process of solving and it is not conducive to maintaining the of species diversity,the genetic algorithm is improved.The parents of the father and the offspring are combined,and the excellent individuals are selected to reconstruct the new population.In order to overcome the over-reproduction of super-individuals,the congestion factor is introduced.The result shows that the improved genetic algorithm improves the convergence and diversity than the original algorithm.2.Based on the operating conditions of the VAWT and the improved genetic algorithm,the CST parameterization method is combined with the multi-flow tube model to optimize the airfoil parameters of the vertical axis wind turbine blade.The reference airfoil is the NACA0015 airfoil which is commonly used in the VAWT,the maximum tangential force coefficient was taken as the optimization objective due to the special operating conditions in which the angle of attack of the blade changes constantly and the tip speed ratio(TSR)changes,the geometric control parameters of the upper and lower surface of the airfoil were chosen as design variables,and the optimized airfoil was obtained through the genetic algorithm.The aerodynamic performance of the original airfoil and the optimized airfoil was calculated by the numerical simulation method based on the Navier-Stokes equation.Compared with the original airfoil,the optimized airfoil has a higher lift coefficient,tangential force coefficient and better stability of stress.3.Aiming at the variable tip speed ratio operation condition of H-type VAWT,the variation law of the angle of attack of the blade with the blade azimuth angle under different tip speed ratios is derived.The jet wind tunnel and the test bench of the H-type vertical axis wind turbine are built.A three-dimensional unsteady viscous flow field was calculated for a H-VAWT with the original airfoil and the optimized airfoil based on the unsteady Reynolds-averaged Navier-Stokes equations(URANS),comparing the calculated results with the experimental values to verify the accuracy of the calculation method.4.For the complex flow field characteristics of H-type VAWT,three typical TSRs are selected,and the instantaneous power coefficients and vorticity cloud diagrams of the two rotors during one rotation cycle are compared and analyzed under different TSRs.The result showed that the optimized airfoil had different improvement effect on the three-dimensional flow field of the VAWT under different TSRs.Under the low TSR,the optimized airfoil can reduce the scale of the dynamic stall vortex on the surface of the blade;under the medium and high TSR,the optimized airfoil can weaken the unsteady motion of the tip vortex of the blade,reduce the spread range of the blade wake,and shorten the length of the wake.Compared with the original NACA0015 airfoil,the optimized airfoil has higher efficiency and wider high-efficiency area,and the wind energy utilization coefficient under the optimal TSR has increased by 17.6%.5.In order to solve the problem of the blade wake and tip vortex of the VAWT,the method of eliminating vortex by aircraft and horizontal axis wind turbine is used for reference,summarized the influence mechanism of tip vortex on the power characteristics of the H-VAWT,took a three-blade H-VAWT as the experimental object,and installed two different types of tip vanes on both ends of the blades.Finally,compared and analyzed the torque coefficients,the pressure distribution of the blade suction surface,the pressure difference of the blade surface and the vorticity cloud of the blade top section.The results showed that the two kinds of the tip vanes can weaken the tip vortex,increase the pressure difference of the blade surface and the power coefficient of the rotor,the tip vanes play a role in power amplification of the VAWT.Aiming at the relationship between the wind energy utilization coefficient of the H-type vertical axis wind turbine and the variation of the tip speed ratio and the urban variable wind speed condition,the relationship between the rotational speed of the vertical axis wind turbine and the output power is analyzed,an optimal tip speed ratio control system for vertical axis wind turbines is proposed.6.For the H-type VAWT installed in the urban area close to the crowd,a CFD method combining URANS and FW-H sound pressure model is proposed to predict the aerodynamic noise.The modified airfoil self-noise model(TBL-i TNO),the improved turbulence noise model(inflow-buck)and the CFD method combined with the URANS and FW-H sound pressure model are used to predict the aerodynamic noise of the same wind turbine model,and compared with the experimental data,the accuracy of the aerodynamic noise prediction of the H-type vertical axis wind turbine is verified by the CFD method combined with the URANS and FW-H sound pressure model.Taking a three-blade H-VAWT as the experimental object,the FW-H sound pressure model based on unsteady flow was used to predict the aerodynamic noise of the H-VAWT,the Fast Fourier Transform(FFT)was used to obtain the noise spectrum of the receiving points.Finally,the influence of tip speed ratio,wind speed,number of blades and position of receiving points on the aerodynamic noise of H-VAWT was analyzed.Finally,Finally,a method for modifying the H-type VAWT blades is proposed to reduce the aerodynamic noise.Compared with the traditional blade-tip,the S-type blade tips and the tooth-shaped groove tip structure have the effect of reducing the aerodynamic noise of the vertical axis wind turbine.The average sound level is reduced by more than 20%,and the noise reduction effect of the toothed groove tip structure is better than that of the S type tip structure.The larger the tip speed ratio,the better the noise reduction effect.When the tip speed ratio is ?=2,the average noise reduction of the tooth-shaped groove tip structure is3 d B,and the average noise reduction of the S-type tip structure is 2.5d B,the declines are 5.3% and 4.4%,respectively.