Study On Aerodynamic And Noise Characteristics Of Vertical Axis Wind Turbine In Urban Environments

Fully utilizing wind energy resources of urban environments is one of the important ways to solve the energy crisis,greenhouse effects and adjust the energy structure global.A Vertical Axis Wind Turbine(VAWT)is more suitable to install in an urban environment due to its simple structure,low cost,and strong adaptability for wind conditions.However,in urban environments,the wind speed is lower,the turbulence intensity is stronger,the requirements of the noise level are higher.Moreover,VAWT works in low Reynolds number(Re)(1×105～5×105)and low tip speed ratio(less than 3)conditions in urban environments generally.These factors result in more complicated unsteady aerodynamic performance and aerodynamic noise characteristics of VAWT.Therefore,this dissertation focuses on a small H-type VAWT and the condition of the low Re and tip speed ratio,studying aerodynamic performance and aerodynamic noise characteristics of VAWT in urban environments using experimental and numerical methods.The major work and results include:(1)An airfoil named LUT airfoil is designed for VAWT by considering the requirements for structure and aerodynamic performance of VAWT airfoil in urban environments and the aerodynamic profile characteristics of VAWT airfoil.The wind tunnel experimental results show that,compared with the traditional airfoils and dedicated airfoils of VAWT,the LUT airfoil shows the higher maximum lift coefficient and lift-drag ratio,the wider low drag areas,good aerodynamic performance after stall,and less sensitivity to roughness.To some extent,the LUT airfoil can improve the aerodynamic performance of VAWT and meet the structural strength and aerodynamic performance requirements for a VAWT in urban environments.(2)Improving the LB dynamic stall model and the cascade model for VAWT,and analyzing the aerodynamic performance of VAWT and its airfoil under different conditions.To some extent,the improved LB dynamic stall model and VAWT cascade model can accurately predict the dynamic aerodynamic performance of VAWT and its airfoil.The results show that the asymmetrical airfoils display the higher dynamic lift coefficient under the low tip speed ratio and positive angles of attack condition,while symmetrical airfoils show the higher dynamic lift coefficient under the negative angles of attack.Symmetrical airfoils can provide a relatively stable load.The effect of incoming turbulence intensity on the dynamic load of airfoils for VAWT is mainly shown after the dynamic stall under low Re condition.Meanwhile,when the dynamic solidity is higher,the tangential force coefficient of the downwind rotor areas of VAWT is less than that of the upwind rotor areas.On the contrary,the value of the tangential force coefficient is a minor difference both at the upwind rotor and downwind rotor areas of VAWT.(3)Studying the output power characteristics of the dual-rotor VAWT,and analyzing the effect of urban environments on the output power of the dual-rotor VAWT.The results show that a reasonable layout of the dual-rotor VAWT can improve the output power of VAWT.In the layout of the dual-rotor VAWT,the smaller the solidity is,the more sensitive the output power of VAWT is to the center distance between the two rotors.The output power of VAWT in the layout of the dual-rotor VAWT displays high asymmetry.The dual-rotor VAWT with higher solidity is suitable to install in the areas of the lower wind power density,while the lower solidity dualrotor VAWT is suitable to install in the areas of the higher wind power density.However,the skewed flow affects the effect of the dual-rotor VAWT,so the layout of the dual-rotor VAWT needs to consider the main wind direction.(4)Investigating aerodynamic noise characteristics of VAWT and its airfoils based on urban environments.The results show that the more the pressure fluctuation frequency on the airfoil pressure surface near the trailing edge is,the more obvious the tone noise feature is.Moreover,the tone noise feature of symmetrical airfoils is more obvious than that of asymmetrical airfoils,the tone noise feature of a thin airfoil is more obvious than that of the thick airfoil.Increasing the turbulence intensity can decrease the aerodynamic noise level of airfoils near the stall.Meanwhile,the blade passing frequency and vortex shedding frequency of the shaft of VAWT are the main low-frequency noise sources under low Re and tip speed ratio.Moreover,the upwind side of VAWT is an important noise source area.In an urban environment,the noise from the shaft of VAWT is not be ignored,because the part of harmonic frequency comes from the vortex shedding frequency of the shaft in the frequency spectrum of VAWT.