本研究探討小型風力機加入外罩後流場的變化，為了瞭解不同型式的外罩產生的效能，利用PROENGINEER 電腦輔助設計軟體將風力發電機外型輪廓畫出，由Gambit產生網格並以Fluent 6.3.23版求解三維穩態不可壓縮的Navier-Stokes方程式以了解流場變化。 一開始先與實驗值互相驗證無外罩的風力機，使用網格數約160萬的結果可有一定的精確性，再探討加入外罩和無外罩的風力機流場分佈與效能，當風力機加上外罩後，得到的風速變大，最後得到的效能也較好。影響外罩的參數有擴散器的長度（L）、入口直徑（D）、擴張的角度以及外緣的長度（T），本研究選用外緣伸長的長度、擴散器出口與中心軸的距離和後段擴散器的擴散角度來分析。 研究與結果顯示，外緣伸長的長度有決定性的效果，且當外緣伸長的越長，得到的效能也較好。擴散器出口與中心軸的距離則必須具有一定長度，若太短或太長皆無法得到好的效能。最後，後段擴散器的擴散角度至少要在14度以上才能得到好的效能。 The aim of this study is to investigate the efficiency and flow field of small wind turbines with diffuser. The wind turbine models were first drawn by the CAD software, ProEngineer. They were input to the grid generation software Gambit to generate grid. The commercial CFD software package, Fluent 6.3.23 version, was then used to solve the Navier-Stokes equations to obtain the flow field and do the performance analysis. In doing the performance analysis, we first compare the power coefficients of bare wind turbines with experimental data. The numerical results show consistent trend with that of experimental data. We then compare the performance and flow field of bare wind turbines and wind turbines with diffuser. The conclusion is that the power coefficients of the latter are higher than that of the former. Three parameters, diffuser length, expansion angle, and flange length, were investigated to determine their effects on the performance of the diffuser. According to the results, the flange length has the decisive effect. A longer flange gives higher power coefficient. There is an optimum value for the diffuser length, too long or too short gives worse result. Finally, expansion angle must be greater 14 degrees if a favorable effect is to be obtained.
