Study On Effect Of Crosswind To Wind Wheel About Stress Strain And Vibration Frequency

The wind turbine is inevitably subjected to the crosswind during the operation, namely with the outside incentives produced by the crosswind during the wind wheel is running, so the crosswind is apparently one of the main causes that the vibrations of wind turbine occurs. Meanwhile, the wind wheel is the main driving force component of the wind turbine, so the study on the change of the response characteristics on wind wheel vibration parameters with the crosswind conditions is the foundation to ensure safe and stable operation of the wind turbine. However, the development is limited by the numerical simulation method such as effective decoupling lag and the infancy of the relevant test means of wind wheel dynamic vibration characteristics, so that the study the mechanism is still not complete interpretation and the related research methods have not been fully developed, so conducting the relevant research about the response of the wind wheel vibration on the condition of the crosswind has good and practical value.Due to the small wind turbine blade has great stiffness and small deformation, this article only considered the effect of the flow field on the structure, so based on analysis of the uniflow fluid-solid coupling, the small horizontal wind turbine whose rotor diameter is 1.4m was simulated under crosswind operating state. Firstly the paper conducted aerodynamic load calculation, and then the study found that the crosswind had the greatest impact on streamline distribution of the blade that was in the downstream state and even the roots of the phenomenon appeared the diversion of flow lines, at the same time revealed the asymmetry of the aerodynamic loads under the crosswind operating state.On the basis of aerodynamic load applied on the wind wheel surface, aiming at maximum stress strain and the average stress strain two kinds of variables, this paper carried out the analysis of stress and strain behavior of the wind turbine under the crosswind conditions: the maximum stress and strain values of wind wheel were present in the wind turbine at the first order symmetric mode in the different crosswind conditions. With the increase of the crosswind angle, when the crosswind angle was less than 5°, the maximum stress and strain of the wind wheel decreased, the maximum stress and strain of wind wheel reached a peak under the crosswind angle 15°or 20°, at this point vibration exciting force reached the maximum, so the crosswind angle was known as "the worst crosswind angle", at the same time, with the increase of the wind wheel rotating speed, the peak of the maximum stress and strain became more the significant. Next the study found the maximum stress and strain existed the migration characteristics under the crosswind conditions: when the crosswind angle was less than 5°, the wind wheel maximum stress and strain were present on the root of the blade 1, while when the crosswind angle was greater than 15°, which was migrated to the middle biased tip portion of the 2 blade, and the crosswind conditions before the worst crosswind angle(crosswind angle of 10° or 15°) was the critical migration angle. At the same time, study found that the average stress and strain of the wind turbines gradually decreased with the increasing angle.To avoid the resonance of the wind wheel, based on the steady-state structure the modal analysis under crosswind conditions was calculated. The study found that with the increasing of the crosswind angle, the vibration frequency of the wind wheel disc effect decreased faster, the change width of the vibration frequency of the first or second order anti-symmetric modes was extremely small, the vibration frequency of the first or second order symmetric modes evenly declined. The sensitivity of dynamic frequency of each vibration mode to the change of crosswind angle was different: The sensitivity of vibration frequencies of the disc effect modes to the changes of crosswind angle was the most significant, the first or second order symmetric modes followed, the first or second order anti-symmetric modes was weakest, at the same time found that reducing the rotor density and elastic modulus, the vibration frequency of the wind wheel with crosswind angle variation regularly conclusions remained unchanged and the sensitivity of symmetric modes vibration frequencies was more prominent with crosswind angle.By the mixing the orthogonal experiment, preliminarily explored that the main factors of the wind wheel vibration frequency under the crosswind(wind speed, wind direction), the study found when the wind wheel vibration mode was different, the crosswind(wind speed, wind direction) to ones had the different factors: the wind speed was the main factor to influence anti-symmetric modes; the wind direction was the main factor to affect the symmetric modes.