Оцінювання інерційних навантажень вітроколеса

Abstract

Подано математичний опис, побудовано та проаналізовано графічні часові залежності інерційних (відцентрових, дотичних, коріолісових) навантажень, які діють на лопаті вітроколеса при їх нерівномірному обертанні навколо трьох осей: башти (при зміні напрямку вітру), вітроколеса (внаслідок взаємодії з повітряним потоком) та власних поздовжніх осей (внаслідок зміни швидкості вітру або навантаження на валу вітроколеса при використанні в якості регулятора потужності вітроустановки механізму повороту лопатей).

Two basic modes of wind turbine functioning (inconstant and permanent) are considered. The first one is limited in time (starting of the wind-wheel, connection with the electrical supply network, normal or emergency stop). In the permanent mode the wind turbine can work perfectly during long time. The inconstant modes are rather dangerous from the viewpoint of dynamics. The starting mode includes: the blade turning from the feathering to optimal position in order to support maximal power takeoff from the wind flow; the change of nacelle position after the wind direction in order to support the perpendicularity of the wind direction to the plane of the wind-wheel rotation; the change of the wind-wheel angular velocity to its nominal value. The situation, when the extreme gust of wind coincides with the change of its velocity, may arise during the functioning of the wind turbine. Also the cyclic character of inertial loading should be taken into consideration when designing the wind turbine. The resonance (the effect of sudden increase of the amplitude of forced oscillations) may arise when the frequency of inertial loading is coming near the frequency of the blade free vibrations. That’s why the purpose of this article is to build and analyze the graphical time dependences of centrifugal, tangential and the Coriolis forces of inertia and the evaluation of their extreme values in order to substantiate the expediency of taking them into consideration when designing the wind-wheels. Mathematical description of the inertial (centrifugal, tangential, Coriolis) loadings, which operate on the wind-wheel blades at their irregular compound motion – rotation round three axes: that of the tower (at the change of wind direction), of the wind-wheel (as a result of interference with air flow) and of own longitudinal axes (as a result of change of wind speed or loading on the wind-wheel billow at the use of the blades traversing gear as the regulator of wind plant power) is presented. Kinematic scheme of the wind turbine when using the mechanism of blades turning, which consists of blade, wind-wheel, nacelle, tower and foundation, is built. Time dependences of inertial loadings in the mode of the wind-wheel starting are shown. The following conclusions were made after analyzing of the obtained results: 1) the greatest influence (about 95% from equivalent inertial loading) on the blades is caused by the inertial loading, which arises at the wind-wheel rotation. Considerably smaller influence (about 5%) is made by the Coriolis force, which arises at simultaneous rotation of the nacelle and the wind-wheel. Less than 1% from equivalent inertial loading is formed by all other centrifugal, tangential and the Coriolis forces; 2) the Coriolis forces make about 10–15% from total loading on the blade of the wind turbine, when aerodynamic forces – about 50–60%, gravitational - 15–25%, centrifugal, tangential forces of inertia and other loadings – 15–25%. That’s why the task of theoretical modeling of the Coriolis inertial forces and taking them into consideration when building the mathematical models of the blade loadings is rather up to date; 3) oscillations frequencies and amplitudes of inertial loadings abruptly increase when rising the angular velocity of wind-wheel, nacelle or blade. Herewith, these frequencies may coincide with the frequency of the blade free vibrations and the resonant modes may rise during compound motion of the system; 4) most of the inertial loadings rise only under unsettled modes of wind turbine functioning, i. e. at sharp changing of wind flow direction or speed. These modes are usually short-term, but they should be taken into consideration when designing wind-wheels to provide the of maximal operation reliability of the wind turbine.