利用外部導風板增進垂直軸風力發電機效能之數值分析

Abstract

本研究旨在透過數值模擬分析外部機翼狀導流板對垂直軸風力發電機(垂直風機)發電效能的影響。藉得數值模擬，不同導流板弦長、不同導流板數量及不同導流板方向設置的垂直風機的發電效能得以相互比較。本研究亦導入多流管理論模型分析安裝導流板後，於高尖端速度比下垂直風機的效能提升及機制。結果顯示，導流板因能有效地加速其鼻端附近的流體，只要其機翼弦長大於0.6倍的轉子半徑，就得以在大範圍的尖端速度比下，最高提升轉子的功率輸出達 30%。然而，使用導流板亦意味著增加整體風機的正投影面積，這會使得整體風機的空氣動力學效率下降。同時，模擬結果亦顯示導流板的方向設置(正對或對稱入口流)會在不同導流板數量下產生不同的功率提升。平均來說，裝有六個導流板的垂直風機會有最佳的效能。最後，我們以3D列印製作了一個24公分大小的模型，並以國立臺灣大學機械工程學系(台大機械系)的低速風洞進行效能提升測試。結果顯示，裝有導流板的垂直風機於自由旋轉下相對無導流板的垂直風機能有更高的轉速。這間接驗證了外部導流板能有效提升垂直風機的效能。

This study is aimed at numerically investigating the effects of exterior airfoil-shaped deflectors on power production of Vertical Axis Wind Turbines (VAWTs). Incompressible flows around VAWTs with various deflector chord lengths, various number of deflectors, and two configurations are simulated. A theoretical muti-streamtube model, which is shown to have a good prediction of the performance of VAWTs with no deflectors at high tip-speed ratios, is also used to calculate the power output of VAWTs with deflectors and theoretically analyze the effects caused by deflectors. The results show that the deflectors, which accelerate the fluids around their noses, are able to enhance the rotor power output up to about 30% over a wide range of tip-speed ratio when their chord length is greater than 0.6 of the turbine rotor radius. However, the implementation of deflectors also implies the increase in the frontal area of VAWT, where the overall aerodynamic efficiency decreases correspondingly. Moreover, simulations show that the deflector orientation (aligned or symmetric to the incoming stream) can generate different power enhancement depending on the number of deflectors, which suggests that VAWTs with 6 deflectors on average has the optimal performance. Finally, a 24-cm model is 3D printed to be experimentally tested the performance improvement in a low-speed wind tunnel in the department of Mechanical Engineering at National Taiwan University (NTUME). The results show that VAWTs with deflectors spins freely at a higher rotation speed than ones without deflectors, which indirectly validate the effectiveness of exterior deflectors in performance enhancement.