使用大渦流模擬對風力發電機尾流之分析

A Study of Wind Turbine Wake Flow by Using Large Eddy Simulation

蔡雨鈞(Yu-Chun Tsai)

指導教授 ： 許政行

中原大學/工學院/機械工程研究所/碩士(2022年)

https://doi.org/10.6840/cycu202200022

摘要

本論文主要在說明利用大渦流模擬(Large eddy simulation, LES)來對風力發電機之尾流做分析。不同於常使用的雷諾平均(Reynolds Average Navier-stokes, RANS)模型，是以渦流的角度觀察流場，可求得於時間及空間的尺度上較精準的模擬結果。
本研究使用計算流體力學(Computational Fluid Dynamics, CFD)軟體ANSYS Fluent求解器求解，以暫態計算之方式進行風力機的運轉模擬，參照各研究中常見風速設定5 m/s、7 m/s、9 m/s、11 m/s、13 m/s、15 m/s六種風速做為數值計算的邊界條件，並利用大渦流模擬(LES)和移動參考座標系(Moving Reference Frame, MRF)進行模擬分析。
本論文討論尾流速度場、尾流下游速度曲線、尾流混合情形和渦旋度分佈與渦流結構；流場分析之結果顯示在速度場中入流風速越快尾流混合位置將會前移約一倍轉子直徑；在速度曲線最高峰值會因為渦流結構的擾動，造成峰值的偏斜而出現軸向不對稱情形。此外發現速度向量在三至四倍轉子直徑的下游區域，於葉尖位置風速有兩個較明顯的峰值；另外發現，在風力機中心位置的一倍轉子直徑處，速度向量出現不平行現象；尾流速度流線擾動之現象，與速度向量圖不平行有相互對應；隨著入流風速越快渦旋強度會變強，渦流在下游區與自由流混合位置將會提前。

關鍵字

大渦流模擬 ； 尾流 ； 計算流體力學 ； ANSYS fluent ； 移動參考座標系 ； 渦旋度

並列摘要

This paper mainly describes the use of Large eddy simulation (LES) to analyze the wake of wind turbines. Different from the commonly used Reynolds Average Navier-stokes (RANS) model, the flow field is observed from the angle of eddy current, and more accurate simulation results can be obtained on the scale of time and space.
In this study, the Computational Fluid Dynamics (CFD) software ANSYS Fluent solver was used to solve the problem, and the operation of the wind turbine was simulated by transient calculation. Six wind speeds of 5 m/s, 7 m/s, 9 m/s, 11 m/s, 13 m/s, and 15 m/s were used as boundary conditions for numerical calculation, and the Large eddy simulation (LES) and the Moving Reference Frame (MRF) for simulation analysis.
This paper discusses the wake velocity field, the downstream velocity curve of the wake, the mixing situation of the wake, the vortex distribution and the structure of the vortex. The results of the flow field analysis show that the faster the inflow wind speed in the velocity field, the faster the wake mixing position will move forward by about approx. Double the diameter of the rotor; at the highest peak of the speed curve, there will be an axial asymmetry due to the disturbance of the eddy current structure, resulting in the deflection of the peak. In addition, it is found that the velocity vector in the downstream region of three to four times the rotor diameter, the wind speed has two more obvious peaks at the blade tip; as the inflow wind speed is faster, the vortex intensity will become stronger, and the vortex will mix with the free flow in the downstream region. will be in advance.

並列關鍵字

LES ； wake flow ； CFD ； ANSYS fluent ； MRF ； vorticity

參考文獻

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