台灣地區颱風風況對風機氣動力負荷影響之研究

Abstract

台灣極具有風能開發之潛力，但也同時面臨颱風所造成風機倒塌的問題，這些風機不泛國際知名風機大廠的產品，且經過國際風機認證，但仍無法存活於嚴苛的颱風風況條件，故風機認證依據之規範(IEC61400-1)內容是否充分考量了颱風風況須要進一步研究。風機設計規範IEC61400-1的設計案例中未包含颱風狀況下的風機工作環境，雖然DLC6與DLC7的設計工況設定為停機，外部風況條件為極端風況，可對應風機於颱風期間的高風速，但此兩種設計負荷案例的風況條件未包含颱風期間風速瞬間變化的陣風情況。有鑑於此，本文將對台灣在颱風期間的風況進行分析，提出符合台灣颱風期間之極端風速與陣風模型，並以此作為風速條件進行風機數值模擬，以了解風機在颱風期間所受之氣動力負荷特性，以供風機設計、採購與補強時參考。 藉由比較氣象學上對於颱風風況之定義以及國際風機設計規範IEC61400-1中對於類似颱風之風況定義與數學模型，設定風機需要考量之颱風風況參數，並依此對颱風期間的彰工測風塔風速量測資料進行統計整理，以評估台灣颱風期間可能面臨之極端風速與陣風，結果顯示台灣彰工地區颱風期間可能面臨之1分鐘平均風速為36m/s，陣風因子為1.26、期間最大風速為64.85m/s。接著以商業軟體ANSYS FLUENT求解RANS方程與SST k-w紊流模型以模擬NREL 5MW風機在颱風期間極端風速與陣風下之流場。陣風期間風機氣動力負荷極值並非發生於風速最大時，且較極端風速為定值情況下之風機氣動力負荷為大，其中阻力為1.50倍、縱搖力矩為1.30倍、轉子力矩為1.40倍而塔頂結構物的平擺力矩則為1.35倍。 由模擬結果可知以極端風速評估風機氣動力負荷會低估風機於颱風期間可能面臨的極端氣動力負荷。因此本文建議常有颱風侵襲的區域在進行風機設計或負荷評估時，除了原先的設計負荷案例DLC6與DLC7外，最好再增加設計工況為停機，外部風況條件為陣風之案例設定。

In Taiwan, the wind turbine that has been certificated by the international certification organization, such as GL, was still collapsed during typhoon. So, it is necessary to discuss if the design requirements of wind tirbine described in IEC61400-1 satisfied the environment of typhoon. There is no design load case defined for the conditions of wind turbine during typhoon in IEC61400-1, the guideline for design requirements of wind turbine. Although the standstill situation and wind condition of DLC6 and DLC7 are corresponding to the wind turbine with extreme wind speed during typhoon, but the gust during typhoon is not included. For these reasons, the recorded wind data during typhoon is analyzed to propose the extreme wind speed and gust model that corresponding to the wind condition during typhoon in Taiwan. Then, the characteristics of aerodynamic load acting on the wind turbine are studied by the numerical simulation of the flow field around the wind turbine with the proposed wind conditions mentioned above to be the reference for design, purchase and reinforcement of wind turbine in this article. According to the statistical analysis of the data that recorded by Chang-Kung anemometer during typhoon, the 1 minute average wind speed is 36m/s, the maximum 3 seconds average wind speed is 45.36m/s, the gust factor is 1.26 and the maximum instantaneous wind speed is 64.85m/s. And then the flow field around the NREL 5MW wind turbine with extreme wind speed and gust mentioned above are simulated by solving the RANS equations and SST k-w turbulence model. The simulating results of the gust case show that the drag and pitch moment of the wind turbine are not the extreme values while the wind speed being the maximum during typhoon. Moreover, the simulating results of the gust case also show that the extreme drag, the extreme pitch moment, the extreme rotor moment and the extreme yaw moment are larger than those of the extreme wind speed case that the wind speed is constant and is equal to the maximum wind speed during gust. The extreme drag of the gust case is 1.50 times of the extreme wind speed case, the extreme rotor moment of the gust case is 1.40 times of the extreme wind speed case and the extreme yaw moment of the gust case is 1.35 times of the extreme wind speed case. According to the simulating results, the extreme aerodynamic loads acting on the wind turbine will be under estimated if the wind condition is the fixed extreme wind speed that is corresponding to the wind condition of DLC6 and DLC7. Therefore, the gust should be considered as one of the wind condition for the design load case with standstill situation.