Aerodynamic Characteristics And Aeroacoustics Of Vertical Axis Wind Turbines

With the rapid development of wind power industry,offshore wind farms with tremendous potential have attracted considerable attention for wind energy conversion and utilization.The advantages in large-scale,installation and maintenance,wind farm layout and aerodynamic noise make vertical axis wind turbine as a research topic.However,the unsteady effects of aerodynamic loads have brought difficulties to the design of vertical axis wind turbines.More progress about the research on noise generation and propagation mechanisms needs to be made to deal with the existed noise pollution problem.Therefore,in-depth study of aerodynamic and aero-acoustic characteristics of vertical axis wind turbines would promote new designs of wind turbines.Accurately simulating dynamic responses of wind turbines would be of great significance to give impetus to the large-scale development of vertical axis wind turbines.In this thesis,study on aerodynamic characteristics and aeroacoustics of H-type vertical axis wind turbines was conducted by several numerical methods.The procedures of aerodynamic responses of vertical axis wind turbines under different working conditions were analyzed carefully.In the study of three-dimensional unsteady numerical simulation of vertical axis wind turbines,the model was validated with experimental data.Then the power coefficient,blade force coefficient and shedding vortices of wind turbines at different tip speed ratios were calculated.The detailed information about the flow field around wind wheel was analyzed.The results showed that,the blade force coefficients changed periodically in revolutions.The force coefficients of blades in the downwind region fluctuated irregularly because blades were subjected to stronger unsteady effects.The generation and shedding of the vortices near blades had obvious regular patterns.With the increase of azimuthal angle,the vortex structures on the blade surface moved gradually from the trailing edge to leading edge until flow separation occurred.And periodic strip shedding vortices were formed at both ends of the blade.Besides,the low-speed wake region gradually shifted downward due to the clockwise rotation of the wind wheel.The generation mechanism of aerodynamic noise of wind turbines and the influence of inflow conditions on noise were studied.After obtaining the flow field characteristics of wind turbines by CFD model,the noise prediction was conducted by using Ffowcs Williams and Hawkings acoustics analogy method.The results indicated that,the thickness and loading noise were dominant noise sources in wind turbine tonal noise.Higher tip speed ratio and higher blade surface load increased the total noise intensity.The increment of sound pressure level caused by high turbulence intensity was relatively small at higher tip speed ratio.The blade leading edge effect was an important noise source of wind turbines.Stronger interaction between vortices and blades made the total noise level increased.Finally,this thesis would provide a value reference for the structural design and noise reduction design of H-type vertical axis wind turbines.It could be exploited for the improvement in the design of new vertical axis wind turbines.