| Vertical axis wind turbines (VAWTs) can immensely overcome inherent defects of horizontal axis wind turbines for the advantages of without active yawing devices and putting devices such as generator and gearbox on the ground. And it will be the trend of new large and highly efficient wind turbines. Attack angle cyclically changes in large range during VAWT running. And it is difficult to get a good aerodynamic evaluation VAWT due to dynamic stall of blade when flow separation and vortex generate in large attack angle condition. Because of alternating and random of external wind loads excitation, it is inevitable that VAWT will vibrate. Rotor of VAWT is rotating machine. It is difficult to get the dynamic characteristics of VAWT due to centrifugal softening effect,stress stiffening effect and Coriolis force effect when VAWT is rotating. And VAWT is in the air flow, aeroelastic effect due to coupling of air and structure will affect dynamic characteristics of VAWT even lead to flutter. Study the nature, centrifugal softening effect,stress stiffening effect and Coriolis force effect are result from coupling of large motion and deformation of structure. Aeroelastic effect is result from coupling of aerodynamic force and structural elastic force due to liquid-soild boundary changing when structure is moving. These coupling issues correspond to interdisciplinary of continuum mechanics and general mechanics and interdisciplinary of aerodynamics and elastic mechanics, and they become the most active subjects in recent years.In this dissertation, Aerodynamic evaluation of VAWT was reviewed. The key of aerodynamic evaluation of VAWT was pointed out. An insight was made into flexible dynamics modeling and modal analysis of VAWT. Aeroelastic stability of VAWT was reviewed also. The principal investigation and conclusions of the dissertation are as follows:①Technical route of MW class VAWT system design was planned. Initial design of 1.2 MW Darrieus type VAWT was done. And parameter designs on subsytem of wind turbine were finished after aerodynamic analysis and structural analysis. Design drawings of wind turbine were accomplished.②Aerodynamic evaluation of Sandia 17m VAWT was done based on double -multiple streamtube aerodynamic model while Gormont,B-L and ONERA semi-empirical dynamic stall model were used. The numerical results were compared with the test results then. And for aerodynamic evaluation of 1.2 MW Darrieus type VAWT, Gormont semi-empirical dynamic stall model was selected, Reynolds number effect,wind shear effect and finite aspect ratios effect were considered also.③According to flexible dynamics modeling method, finite element formulation of dynamical equations of beam in centrifugal field was got. Dynamical frequecies (Campbell diagram) of VAWT were calculated. Structure design can be revised in turn then. The influences of centrifugal softening effect,stress stiffening effect and Coriolis force effect on Campbell diagram were analyzed also.④Based on second development of ANSYS, user-defined element matrix27 was used. Finite element formulation of VAWT dynamic equations were built as aeroelastic effect of VAWT was considered. Finite element matrices of blade element for aeroelastic stability of VAWT were given out. Then aeroelastic stability analysis of 1.2 MW Darrieus type VAWT was done. The flutter frequency and instability rotating speed of the VAWT were got when the VAWT was working at rated wind speed.⑤Coriolis force first order term exists in structural dynamic equation while structure is in centrifugal field. And structural modal vectors are complex. In general structural dynamic analysis, imaginary component is be abandon so as to make complex modal vectors to be real. It is identified that complex modal vectors correspond to coupling motion also called polarized motion of structural mass point, while real modal vectors correspond to linear motion of structural mass point. The simplified treatment of real modal vectors instead of complex modal vectors will cover the nature of motion of vibration system in centrifugal field. Coriolis force first order term do not owe to real physical damping, does not produce system attenuating vibration. For a spring-mass vibration system with two degrees of freedom in a centrifugal field, system modal vectors are complex vectors due to Coriolis force. System complex modal vectors lead to polarized circle motion of the mass. For a mass-spring-damping vibration system with two degrees of freedom in a centrifugal field, structure damping gives out attenuation of free system vibration. Individual complex modal vector is associated with polarized helix circular motion of the mass.⑥Finite element formulation of dynamic equation of cantilever beam in centrifugal field was built. The first two modes of cantilever beam were researched. The relationship affected by Coriolis force between dynamic frequencies of cantilever beam and centrifugal rotational speed were analyzed. It is identified that modal vectors of translation and angle of rotation of cantilever beam in centrifugal field are complex modal vectors. The first two complex modal vectors of translation correspond to structural mass polarized elliptical motion trajectory. And the first two complex modal vectors of angle of rotation correspond to rotation superimposed on translational polarized elliptical motion. Elliptical equation is satisfied with two rotation components. |
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