| 摘要: | 本論文旨在以計算流體力學方法模擬葉片氣動力負載。風機葉片氣動力負載計算主要有兩種，分別為葉片元素動量理論(Blade Element Momentum, BEM)及計算流體力學(Computational Fluid Dynamics, CFD)，過去由於電腦計算速度較慢，以葉片元素動量理論(Blade Element Momentum, BEM)為主要方法，該方法須仰賴二維翼型的升力與阻力係數實驗數據，並以理論公式修正，以符合實際三維流場的影響，這對風機設計上帶來許多限制，近年來隨著電腦軟體的快速發展，電腦已可以負荷複雜的三維風機流場，計算流體力學不需依賴任何葉片翼型的氣動力實驗數據即可計算並可對葉片周圍的流場進行細部的探討，因此吸引許多研究的興趣。本研究使用商用軟體ANSYS Fluent，穩態RANS方程式，SST k-ω紊流模型，以移動座標方式(Moving Reference Frame, MRF)模擬計算氣動力負載，分析的條件參考歐盟Mexnext計畫之NewMexico 風洞實驗，條件為-2.3度節距角(pitch angle)，軸向均勻流10 m/s、15m/s、24 m/s三種風速，模擬結果與實驗結果實施比對，並探討葉片的氣動力負載，分析項目包括推力、扭矩、葉片表面壓力、正向力、切向力、升力係數、阻力係數及流線。結果顯示模擬的旋轉現象與理論相符，即翼根處有失速延遲(stall delay)的現象；而在翼尖處有翼尖損失(tip loss)的現象。由於模擬的正向力與切向力較高，使得扭矩值平均大於實驗值約15.33%，在高風速24 m/s與實驗誤差最大，葉片處於失速狀態流場較不穩定，推力計算誤差最大達16.4%。本文另以ANSYS Fluent模擬二維翼型之升阻力係數，結果顯示與與實驗值相近，可做為替代葉片元素動量理論中所需之二維翼型的升力與阻力係數實驗數據，以提升風機設計與模擬的效率。;This research simulates and calculates aerodynamic loads using Moving Reference Frame (MRF) in the commercial software ANSYS Fluent. The flow field is modeled using steady-state RANS equations and SST k-ω turbulence model. The analysis conditions refer to the NewMexico wind tunnel experiment in the EU Mexnext project. The pitch angle is -2.3 degrees, and the axial wind speed is 10 m/s, 15 m/s, and 24 m/s, respectively. The simulation results are compared with the experimental results of EU Mexnext, and the aerodynamic load of the blades is discussed. The analysis items include thrust, torque, blade surface pressure, normal force, tangential force, lift coefficient, drag coefficient, and streamline. The results show that the simulated rotation phenomenon is consistent with the theory. There is a stall delay at the blade root and tip loss at the blade tip. Due to the high simulated normal and tangential forces, the relative error of torque is about 15.33%. The error is the largest at the high wind speed of 24 m/s. The blade is in a stalled state, the flow field is relatively unstable, and the thrust calculation error can be as large as 16.4%. We also use ANSYS Fluent to simulate the lift and drag coefficient of the two-dimensional airfoil. The results show that it is close to the experimental value. It can be used to replace the experimental data of the lift and drag coefficients of the two-dimensional airfoil required in the blade element momentum theory to improve the wind turbine design and simulation efficiency. |
